APD 加电极 大电场下增加碰撞电离概率且不易被缺陷捕获

Avalanche photodiodes (APDs) featuring internal multiplication hold great promise for high-sensitivity detection in optical systems. The gain-bandwidth product (GBP) comprehensively characterizes APDs’ overall performance, intrinsically linked to the effective impact ionization ratio, namely the k factor. An ultralow k factor suggests an ultrahigh GBP in theory, underscoring that one of the keys for the APD design should focus on minimizing the k factor. Here, we propose and experimentally demonstrate a novel waveguide Ge/Si APD with a record-high GBP of 5580 GHz (more than 500% higher than those reported previously), corresponding to a high gain of 209 and a bandwidth of 26.7 GHz when operating under −30 dBm input optical power. Introducing a PN junction as the multiplication region leads to a highly non-uniform electric field distribution for impact ionization and enables impact-ionization engineering without requiring complex multi-layer epitaxy processes. The effective k factor is measured to be as low as 0.011, which is even much lower than the intrinsic value of bulk silicon. With the present APDs, very high-speed PAM4 signals with a bit rate of up to 160 Gbps are received successfully with a clear eye-diagram. The present APD is further packaged with a transimpedance amplifier chip for 50G-PON systems, successfully achieving a high sensitivity of −26.5 dBm for 50-Gbps NRZ signals. Such high-performance Ge/Si waveguide APDs developed with simple fabrication processes show great potential for photodetection across diverse application scenarios.

Abstract If the impact ionization occurs in a region of high electrical field then it can result in avalanche multiplication of carriers. This process is used in avalanche photodiodes enabling individual photons to be detected when the incident flux of light is very low. HgCdTe is an almost ideal material for avalanche photodiodes, however to achieve the highest performance in near-room temperatures, a careful design of device structure is needed, to reach the highest performance in near-room temperatures. N+-ν-p-P+ photodiode meets the requirements of the separated absorption and multiplication regions. This paper describes the results of research aimed at investigation of the impact ionization mechanism in HgCdTe N+-ν-p-P+ photodiode optimized for 8 μm cut-off wavelength at 230 K. The results show that the parameters of the ν-region greatly influenced on the distribution of the electric field and the generation rate due to the impact ionization. In addition, ν-region has the effect on reduction of undesirable tunneling in the space charge region. For this purpose, it is necessary to keep the doping in this region as low as possible and to extend the energy gap in relation to the absorbing region.

The simulation of HgCdTe avalanche photodiode (APD) gains and excess noise factor is revisited through the development of a simplified Monte Carlo (MC) model, with the aim of a fast and accurate simulation enabling the design of improved APDs. In this first step, the model is based on a one-dimensional junction approximation with a constant electric field, in which electrons drift and gain energy while losing some of that energy by phonon emission, and where their impact ionization probability is evaluated at each time step. These simplifications allowed us to limit the model to six parameters, of which four were chosen to be adjustable as a function of APD cadmium composition, while the other two were fixed. After calibration, the model successfully matched the experimental gain characteristics of two APDs in the short-wave infrared (SWIR) and mid-wave infrared (MWIR), with simulation duration short enough to be compatible with design purposes. However, a unique set of parameters must be obtained to adjust the simulation to the excess noise factor. This indicates that the dependence of the impact ionization probability as a function of the electron energy is smooth, consistent with band structure calculation. Finally, the influence of the multiplication junction thickness on the APD characteristics was explored with our model, revealing an excess noise factor that is independent of the junction width.

Avalanche photodiodes (APD) can amplify the photoelectric signal based on the avalanche multiplication effect of carrier to improve the sensitivity of detection. They have the characteristics of low noise and high gain, so they are suitable for long-distance optical communication. In this work, a multi-stage avalanche photodiode structure with SAGCM (Separated Absorption, Grading, Charge and Multiplication region) is proposed based on Impact Ionization Engineering (I2E). The photocurrent, dark current, electric field, gain and noise characteristics of InGaAs/InAlAs avalanche photodiodes are studied by optimizing the grading layer's thickness and doping concentration. According to the final simulation results, the optimized avalanche photodiodes has low excess noise. At 60 V voltage and 300 K temperature, the noise factor k value (the ratio of impact ionization coefficients) of the five-stage APD is 0.012, and the gain can reach 430.

Abstract This paper has clarified the performance parameters estimation of high speed silicon/germanium/InGaAsP avalanche photodiodes wide bandwidth capability in ultrahigh speed optical communication system. The basic structure configuration of avalanche photodiode is clarified. The basic depletion region configuration schematic view is demonstrated. As well as the maximum electric field is indicated for impact ionization through avalanche photodiode in the presence of load. Various avalanche photo-detectors multiplication factor is clarified versus reverse bias voltage at room temperature. Different avalanche photo-detectors dark current is measured against avalanche photo-detectors volume at room temperature. Various avalanche photo-detectors effective doping concentration is demonstrated against ambient temperature variations. Si/Ge/InGaAsP avalanche photo-detectors excess noise factor is demonstrated versus the ionization ratio at room temperature (T = 300 K) and different ambient temperature (T = 350 K and T = 400 K). Various avalanche photo-detectors excess noise factor is measured clearly versus the multiplication factor at room temperature. Si/Ge/InGaAsP avalanche photo-detectors excess noise factor is demonstrated versus reverse bias voltage at room temperature. Si/Ge/InGaAsP avalanche photo-detectors noise equivalent power is clarified versus multiplication factor at room temperature. Various avalanche photo-detectors noise equivalent power is studied versus temperature variations. Si/Ge/InGaAsP avalanche photo-detectors sensitivity is measured in relation to the temperature variations. Different avalanche photo-detectors sensitivity is demonstrated in relation to reverse bias voltage variations at room temperature.

Miniaturized infrared spectrometers are vital for portable sensing, yet most single-detector computational schemes prioritize spectral encoding while overlooking weak-signal requirements in mid-infrared detection, where high absorption, low dark current, and internal gain are essential. Here, we propose and numerically validate a voltage-programmable spectral sensing concept based on a graded-bandgap HgCdTe avalanche photodiode. In this design, the composition gradient is repurposed as an active spectral-encoding coordinate. Through bias-dependent depletion, the device selectively accesses different absorption depths, while an N/P double-buffer architecture confines the high electric field within the wide-bandgap multiplication region, preserving avalanche gain while suppressing tunneling-related dark current in the absorber. Crucially, the multi-physics TCAD framework—incorporating wavelength-dependent absorption, carrier transport, tunneling, recombination, and impact ionization—is rigorously calibrated against experimental data from a baseline HgCdTe diode. These experimentally anchored simulations reveal distinct electrical fingerprints across 3–7 μm, driven by the coupled effects of absorption depth, photon flux, and wavelength-dependent avalanche path length. Compared to a conventional PIN structure, this architecture reduces dark-current density by one to two orders of magnitude at comparable gain. By processing these fingerprints with a noise-aware dual-branch neural network, discrete-band spectral reconstruction achieves a mean R2 of 0.9894 and a total-energy error of 3.21%. This work establishes a detector-physics-driven route toward filter-free, gain-assisted mid-infrared spectral sensing.

AlxGa1-xAsySb1-y grown lattice-matched to InP has attracted significant research interest as a material for low noise, high sensitivity avalanche photodiodes (APDs) due to its very dissimilar electron and hole ionization coefficients, especially at low electric fields. All work reported to date has been on Al concentrations of x = 0.85 or higher. This work demonstrates that much lower excess noise (F = 2.4) at a very high multiplication of 90 can be obtained in thick Al0.75Ga0.25As0.56Sb0.44 grown on InP substrates. This is the lowest excess noise that has been reported in any III-V APD operating at room temperature. The impact ionization coefficients for both electrons and holes are determined over a wide electric field range (up to 650 kV/cm) from avalanche multiplication measurements undertaken on complementary p-i-n and n-i-p diode structures. While these ionization coefficients can fit the experimental multiplication over three orders of magnitude, the measured excess noise is significantly lower than that expected from the β/α ratio and the conventional local McIntyre noise theory. These results are of importance not just for the design of APDs but other high field devices, such as transistors using this material.

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Abstract. Avalanche photodiodes (APDs) are critical photodetection devices for high sensitivity and high-speed sensing. Great efforts in bandgap engineering and impact-ionization engineering have been put to achieve high gain-bandwidth products. Plasmonic optical antenna (POA) techniques can change the near-field distributions of the illumination light and thus provide an effective approach to achieve simultaneous enhancement of the gain and the detection speed. We report a metallic circular disk POA array-enhanced APD, where the circular disk POA array was fabricated on top of the p-doped side of the GaAs p-i-n APD. The electric field (E-field) distribution were simulated. The gain and the frequency response of the APD POA-enhanced APD were measured and compared with a reference APD without the POA array. The POA-enhanced APD shows a simultaneous enhancement in the gain and the detection speed.

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This letter presents a new Si CMOS linear-mode avalanche photodiode (APD) based on an electric field distribution formed by field-line crowding. In this structure, a spherical avalanching electric field is enforced by field-line crowding due to the curvature of the half-sphere cathode (n-well). The electric field extends radially and, therefore, the entire low-doped epitaxial layer serves as charge collection zone. This APD can provide high responsivity and bandwidth due to its thick absorption zone and drift-based carrier transport. Measurements using a 675 nm laser source at 200 nW optical power show a maximum bandwidth of 1.6 GHz while the responsivity is 32 A/W. In addition, a maximum responsivity of 3.05 $\times \,\,10^{3}$ A/W at 5 nW optical power is achieved. Due to the high avalanche gain, large bandwidth, and CMOS compatibility without any process modification, this APD is a promising optical detector for many applications.

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Avalanche photodiodes (APDs) demand multiplication materials with low ionization coefficient ratio (k) for high-speed and high-sensitivity photodetection. Germanium/Silicon (Ge/Si) APDs have been preferred for a decade, leveraging the exceptional multiplication property of Si and inherent complementary metal-oxide-semiconductor (CMOS) compatibility. However, the bandwidth remains tens of gigahertz, fundamentally limited by unexpected dual-carrier multiplication in high-k Ge. Here, we transcend this material limitation by introducing a uni-multiplication-carrier concept. Through a separated absorption-charge-cliff-multiplication structure, we elaborately tailor the electric field to gradient distribution within a thin Ge region, establishing electron-dominated multiplication with a significantly reduced k. Experimentally, the device achieves a record-high bandwidth of 105 GHz at a gain of 7. This enables 8×260 Gb/s signal reception, previously only achieved by gainless photodetectors, while providing 9 dB sensitivity improvement. This work paves the way for amplifier-free optical communications, ultra-precise optical sensing, and large-scale optical computing. Researchers shatter the bandwidth record of avalanche photodiodes to 105 GHz using a uni-multiplication-carrier concept. This breakthrough paves the way for next generation optical interconnects and computing.

GeSn-based avalanche photodiode operating in shortwave infrared wavelength was demonstrated in this work. A separate absorption and charge multiplication structure was employed to take advantage of long wavelength absorption in GeSn and low impact ionization ratio of Si. Due to lattice mismatch between Si and GeSn that would degrade GeSn material quality if with direct growth, a 240-nm-thick Ge buffer was utilized, which simultaneously allows for the transporting photo generated electrons from the GeSn absorber to Si multiplication layer. Spectral response showed the cutoff wavelength beyond 2.1 μm at room temperature. Dark current and capacitance–voltage measurements indicated a punch-through voltage of −10 V. The measured responsivities were 0.55 and 0.34 A/W under 1.55 and 1.9 μm excitation lasers, respectively. The maximum gain was obtained as 3.44 at 77 K under 1.9 μm laser. Even at 250 K, the calculated gain was greater than unity. Simulation of the electric field distribution revealed that the GeSn is partially depleted at operating voltages, which can be improved by reducing the background doping levels in the GeSn absorber and Ge buffer layers.

We present ultrafast electron-beam-induced current (EBIC) measurements using an ultrafast scanning electron microscope (USEM) to investigate picosecond-scale transient behavior in semiconductor devices. This pump–probe technique enables spatially resolved observations of electric field dynamics at the micrometer to nanometer scale. We demonstrate this approach through a transient analysis of a dynamically biased avalanche photodiode (APD). Experimental results, supported by an equivalent circuit model, reveal that the gain dynamics under pulsed reverse bias are governed by the device's voltage-dependent capacitance. Furthermore, the radial dependence of the transient response highlights the ability of the method to resolve spatial variations in carrier dynamics. This technique offers insights into carrier transport, electric field distributions, and transient phenomena in a wide range of electronic and optoelectronic devices.

In this study, the effect of electrode shape difference on the height of the Schottky barrier and the electric field in flexible photodiodes (PDs) has been investigated. For this purpose, three different electrode designs were prepared on three flexible FR4 layers that were coated with Zinc Oxide (ZnO). The printing circuit board (PCB) method was used to create these copper electrodes. The asymmetry of the PD electrodes and the difference in the height of the Schottky barrier has led to the creation of self-powered PDs. The effect of the amount and shape of the distribution of internal electric fields generated in the PDs and its effect on the parameters of the PDs has been investigated with the help of simulations performed in COMSOL software. The photocurrent of the sample with circular and rectangular electrodes was equal to 470 µA in 15 V bias, which was twice as good as a sample with an interdigitated MSM structure. Also, this sample had the best response time among these three samples, which was equal to 440 ms.

This paper presents a CMOS-integrated linear-mode avalanche photodiode based on electric field-line crowding (EFLC-APD) to form an effective multiplication zone and a wide absorption zone. The EFLC-APD possesses a hemispherical avalanching electric field at the n-well/p- epi junction formed due to the curvature of the half-sphere cathode. A lower electric field extends radially across the entire volume of the EFLC-APD towards the substrate and towards the surface anode. Because of such a distribution of the electric field, electrons photogenerated within the whole volume drift towards the cathode. Therefore, the EFLC-APD provides a large sensitive-area to total-area ratio while offering high responsivity and bandwidth for red and near-infrared light due to its thick absorption zone and drift-based carrier transport. It is shown that the electric field distribution can be modified by the design parameters such as cathode radius and diode size in addition to doping profiles. The EFLC-APD achieves a responsivity-bandwidth (R-BW) product of 49.5 $\frac{\mathrm{A}}{\mathrm{W}}\cdot$GHz, corresponding to the responsivity and bandwidth of 33 A/W and 1.5 GHz, respectively, at the wavelength of 850 nm. In addition, a maximum responsivity of 3.05 $\times\, 10^{\mathrm{3}}$ A/W at 2 nW optical power is achieved for the red and near-infrared spectral range. Noise characterization resulted in an excess noise factor F = 6 measured at an avalanche gain of 56.7. Due to the high sensitive-area to total-area ratio, high responsivity, large bandwidth, and CMOS compatibility, this APD is a promising optical detector for many applications.

We demonstrate a silicon-germanium avalanche photodiode with record-high bandwidth of 67 GHz under a modest gain of 6.6, by levering the gain and bandwidth through comprehensively manipulating photocurrent density and electric field in multiplication region.

Avalanche photodiode (APD) is commonly used as a receiver in optical communication and light detection and ranging (LIDAR), offering highly sensitive photodetection capabilities. A key strategy for improving the gain-bandwidth product (GBP) of the APD involves the optimization of the electric field distribution using the charge layer. However, traditional modulation methods to adjust the carrier transport and avalanche process using the charge layer often face challenges (inefficiency and non-uniformity). An InGaAs/Si APD based on the wafer bonding method with a GBP up to 1.03 terahertz (THz) is reported theoretically in this work. The charge layer and groove rings are inserted at the InGaAs/Si bonded interface to modulate the electric field in the APD effectively, demonstrating low dark current and reduced avalanche bias of the device. This approach induces a dramatic and rapid variation of the electric field at the interface while reducing the gradient of the electric field in the multiplication layer. Additionally, the indirect impact of the groove ring on mitigating the adverse effects of the lattice mismatch is pointed out, and the optimal doping concentration range of the charge layer is identified to enhance the modulation effect of the electric field for stronger impact ionization. These findings provide valuable insights for the next-generation InGaAs/Si APDs with high GBP for high-speed data transmission.

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Avalanche photodetectors are renowned for their exceptional sensitivity and high gain-bandwidth product, making them highly promising for optical communications, quantum technologies, LiDAR, and biosensing. This paper presents a lateral separate absorption charge multiplication silicon-germanium avalanche photodiode designed for O-band operation. The electric field distribution was strategically designed to minimize dark current and enhance gain. A tapered input waveguide and a distributed Bragg reflector were integrated to improve responsivity. The device achieves a dark current of only 8.4 μA at 12.5 V reverse bias with an input optical power of −24 dBm and demonstrates a record-high gain-bandwidth product of 7564 GHz. High-speed eye diagram measurements confirm its support for 100 Gbps NRZ and 200 Gbps PAM4 signals, with sensitivities of −17.1 dBm and −9.6 dBm, respectively. Eye diagram validation at 200 Gbps PAM4 was also conducted across eight avalanche photodiodes aligned with an eight-channel dense wavelength division multiplexing system.

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This article deals with the modeling and analysis of the dark count rate (DCR) of single photon avalanche diodes (SPAD) in two models of local and non-local electric field. In the non-local electric field models, the avalanche probability and band-to-band tunneling rate are different from the local models. DCR output is evaluated in two different complementary metal oxide semiconductor (CMOS) processes, of 0.15 μm and 0.18 μm. The non-local avalanche probability is based on considering a non-local dependence of impact ionization on the electric field. At high electric fields, the local model predicts the ionization distance to be negligible and therefore the avalanche probability was not calculated accurately. The results show that the non-local model is closer to the data obtained from the experiment than the local model.

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Abstract This paper studies the implication of impact ionization due to a high electric field on the improvement of the photovoltaic solar cell efficiency. A high electric field existing in the space charge region (SCR) of the solar cell induces the generation of additional free carriers by accelerating the photogenerated electron-hole pairs which collide with the lattice of the semiconductor material. The resultant current taking into account this carriers’ multiplication (CM) is calculated and the maximum efficiency of the photovoltaic solar cell is evaluated. The found results show that CM in photovoltaic solar cell occurs in a definite range of the electric field near to the pn-junction and could improve significantly his efficiency for more than 5% at an electric field less than 4 × 105 V/cm, depending on the width of the space charge region or the multiplication region. The usable range of the electric field for CM in solar cell is linked to the type of semiconductor material used.

Avalanche multiplication characteristics in a reverse-biased homoepitaxial GaN p–n junction diode are experimentally investigated at 223–373 K by novel photomultiplication measurements utilizing above- and below-bandgap illumination. The device has a non-punch-through one-side abrupt p–-n+ junction structure, in which the depletion layer mainly extends to the p-type region. For above-bandgap illumination, the light is absorbed at the surface p+-layer, and the generated electrons diffuse and reach the depletion layer, resulting in an electron-injected photocurrent. On the other hand, for below-bandgap illumination, the light penetrates a GaN layer and is absorbed owing to the Franz–Keldysh effect in the high electric field region (near the p–n junction interface), resulting in a hole-induced photocurrent. The theoretical (non-multiplicated) photocurrents are calculated elaborately, and the electron- and hole-initiated multiplication factors are extracted as ratios of the experimental data to the calculated values. Through the mathematical analyses of the multiplication factors, the temperature dependences of the impact ionization coefficients of electrons and holes in GaN are extracted and formulated by the Okuto–Crowell model. The ideal breakdown voltage and the critical electric field for GaN p–n junctions of varying doping concentration are simulated using the obtained impact ionization coefficients, and their temperature dependence and conduction-type dependence were discussed. The simulated breakdown characteristics show good agreement with data reported previously, suggesting the high accuracy of the impact ionization coefficients obtained in this study.

Digital alloy and random alloy Al_0.85Ga_0.15As_0.56 Sb_0.44 avalanche photodiodes (APDs) exhibit low excess noise, comparable to Si APDs. Consequently, this material is a promising multiplication layer candidate for separate absorption, charge, and multiplication structure APDs with high gain-bandwidth product. Characterization of the impact ionization coefficients of electrons (<italic>α</italic>) and holes (<italic>β</italic>) plays an important role in the simulation of avalanche photodiodes. The multiplication gain curves of eight p⁺-i-n⁺ and n⁺-i-p⁺ APDs covering a wide range of avalanche widths have been used to determine the electric field dependence of the impact ionization coefficients of Al_0.85Ga_0.15As_0.56Sb_0.44. A large impact ionization coefficient ratio between that of electrons to holes was seen across a wide electric field range. Simulations of the avalanche multiplication in these structures using a random path length (RPL) model gave good agreement with experimental results over almost three orders of magnitude, and a mixed injection method was employed to verify the extracted impact ionization coefficients. Interestingly, no difference in the impact ionization coefficients was seen between digital alloy and random alloy Al_0.85Ga_0.15As_0.56Sb_0.44. This knowledge of impact ionization coefficients is beneficial for the future utilization of the Al_xGa_1-xAs_ySb_1-y material system.

Electron and hole impact ionization coefficients are obtained from measurements of high‐Al content AlxGa1‐xN p–n diodes grown on AlN substrates. The photomultiplication method using a 193 nm pulsed laser is applied to measure the multiplication factor. The impact ionization coefficients are modeled using Chynoweth's formulation, based on electric field profiles determined from the solution of Poisson's equation. A least‐squares fit of the theoretical multiplication factor to the measured multiplication factor yields the impact ionization coefficients and the extracted electron impact ionization coefficients are consistent with previous numerical predictions. Furthermore, the theoretical breakdown voltage and critical electric field are computed based on the extracted impact ionization coefficients. These results provide much‐needed data to further optimize the design of optoelectronic, power switching, and high‐power RF devices based on ultrawide bandgap AlGaN.

The hole impact ionization coefficient (IIC) of <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga₂O₃ in the <inline-formula> <tex-math notation="LaTeX">$\langle 010\rangle $ </tex-math></inline-formula> direction is determined by numerical simulation, as <inline-formula> <tex-math notation="LaTeX">$\beta ({E}\,) = 4.0\times 10^{5} \cdot exp(-3.1\times 10^{6}/{E}\,)$ </tex-math></inline-formula>. The simulation model reproduces the experiment of the Schottky barrier diode (SBD) operation, and the investigation of the IIC is performed by varying the value to obtain the matched breakdown voltage at the reversed bias operation. The breakdown simulation results are consistent with the experimental results, with only small errors. By comparing the input modeling with the electron-only impact ionization, hole impact ionization is dominant for SBD breakdown operations.

For developing high-performance, reliable, and robust electronic devices, fundamental analysis of the hot carrier dynamics, high field transport, and electrical breakdown mechanisms in transition metal dichalcogenide field effect transistors is essential, which is largely unknown. In this paper, using a combination of electrical measurements, high-field spatial electroluminescence measurements, and theoretical models, it is presented that the impact ionization in MoS2 is mediated via defects, i.e., assisted via defect-induced trap states. Several unique observations, such as threshold voltage left-shift, increased subthreshold slope, anticlockwise hysteresis in the output characteristics, and bias-dependent redistribution of the electric field, are recorded when biased in the impact ionization regime, which we discover is due to the field-dependent dynamic occupancy of the defect states. Finally, we confirm a unified mechanism of high field breakdown as a competition between avalanche breakdown and minority carrier injection-induced breakdown from the variation of spatial electroluminescence with the gate voltage.

Carrier multiplication via impact ionization in two-dimensional (2D) layered materials is a very promising process for manufacturing high-performance devices because the multiplication has been reported to overcome thermodynamic conversion limits. Given that 2D layered materials exhibit highly anisotropic transport properties, understanding the directionally-dependent multiplication process is necessary for device applications. In this study, the anisotropy of carrier multiplication in the 2D layered material, WSe_2, is investigated. To study the multiplication anisotropy of WSe_2, both lateral and vertical WSe_2 field effect transistors (FETs) are fabricated and their electrical and transport properties are investigated. We find that the multiplication anisotropy is much bigger than the transport anisotropy, i.e., the critical electric field (E_CR) for impact ionization of vertical WSe_2 FETs is approximately ten times higher than that of lateral FETs. To understand the experimental results we calculate the average energy of the carriers in the proposed devices under strong electric fields by using the Monte Carlo simulation method. The calculated average energy is strongly dependent on the transport directions and we find that the critical electric field for impact ionization in vertical devices is approximately one order of magnitude larger than that of the lateral devices, consistent with experimental results. Our findings provide new strategies for the future development of low-power electric and photoelectric devices. Graphical Abstract

Geiger-mode avalanche photodiodes (GmAPDs), also referred to as single-photon avalanche diodes (SPADs), are designed and fabricated by our group at MIT Lincoln Laboratory. When bonded to a readout integrated circuit (ROIC), they form a system that can timestamp single photon arrival with sub nanosecond precision. When the pixels are armed in Geiger mode, they detect photons by creating an avalanche of electron-hole pairs in the detector material that can be detected by a ROIC. This paper explores a phenomenon known as afterpulsing, which can manifest itself as an increase in detector noise, or dark count rate. Afterpulsing occurs due to defects in the device structure that cause charge carriers from a previous avalanche to get trapped within the impurities of the device. If the extra charge carriers aren’t provided enough time to depopulate from the traps, the re-biasing of the individual device back into Geiger-mode operation has a time-based, statistical impact on the likelihood that the trapped carrier causes a secondary avalanche to occur upon re-arm. We investigate afterpulsing using a MIT Lincoln Laboratory designed 32x32 asynchronous readout integrated circuit bump-bonded to a InGaAs/InP 1550nm GmAPD array. This paper reports on how afterpulsing is affected by changing operating temperature, applied overbias voltage, and/or individual pixel holdoff time. Additionally, methods of determining afterpulsing with on-ROIC pixel interarrival data are discussed and best operating parameters to minimize afterpulsing for our GmAPD and ROIC are presented.

Avalanche photodiodes (APDs) play a crucial role in high-speed fiber-optic communication and eye-safe light detection and ranging (LiDAR). This work investigates the temperature-dependent behavior of GaAsSb/AlGaAsSb Separate Absorption, Charge, and Multiplication (SACM) APDs to understand their low-temperature performance, noise characteristics, and dark current mechanisms. The study employs temperature-dependent current-voltage (I-V), capacitance-voltage-temperature (CVT), and capacitance-voltage-frequency (CVF) measurements to explore charge trapping effects, impact ionization, and avalanche gain stability. At low temperatures (<100K), an anomalous negative differential resistance (NDR) effect is observed in the dark current characteristics, suggesting the presence of trap-assisted charge storage and release mechanisms. Activation energy analysis indicates that trap-assisted tunneling (TAT) dominates at high biases, while Shockley-Read-Hall generation-recombination (G-R) currents dominate at lower biases. Frequency-dependent capacitance measurements confirm deep-level trap activity, affecting electric field distribution and depletion characteristics. The results suggest that optimizing the heterostructure design to mitigate charge trapping and enhance impact ionization uniformity is critical for achieving high-performance APDs suitable for LiDAR and optical communication applications.

This paper reports a high-performance InGaAs/Si avalanche photodiode (APD) utilizing a microcrystalline germanium (μc-Ge) interlayer bonding technique. This technique enables the formation of a high-quality InGaAs/Si heterojunction with a void-free, high-strength, and oxide-free bonded interface, effectively suppressing dislocation formation and elemental interdiffusion. The device demonstrates high responsivities of 68 A/W and 135 A/W at wavelengths of 1310 nm and 1550 nm, respectively, with avalanche gains of 106.25 and 190, respectively, significantly outperforming previously reported Ge/Si and various InGaAs-based APDs. Further observation shows that the punch-through voltage increases with rising optical power, attributed to the space charge effect caused by the hole potential well at the μc-Ge bonded interface. Additionally, a defect-assisted tunneling mechanism for interfacial carrier transport is revealed. This work presents an effective technological pathway for the development of high-performance, low-noise III-V/Si integrated photodetectors.

The work investigates the photoelectric characteristics of an avalanche photodiode based on an axisymmetric mesa Ge-on-Si structure with separate absorption, charge and multiplication (SACM) and a technological sidewall tilt of about 5°. The photodetector is intended for near-infrared radiation detection ($\lambda=1.55 \mu \mathrm{~m}$) in the linear mode. To improve electric-field localization in the iGe multiplication region and suppress leakage along the $\mathrm{Ge} / \mathrm{SiO}_{2}$ sidewall surface, an additional doped $\mathrm{Ge}(\mathrm{p}+)$ layer is proposed to shift the peak electric field away from the surface. The TCAD model parameters were calibrated against experimental data, taking into account various carrier recombination mechanisms and trap states in the bulk and at the $\mathrm{Ge} / \mathrm{Si}$ and $\mathrm{Ge} / \mathrm{SiO}_{2}$ interfaces. It is shown that the $\mathrm{Ge}(\mathrm{p}+)$ layer reduces the dark current and increases the achievable gain. Current-voltage characteristics, electric-field distributions, and gain behavior near breakdown were obtained. The maximum gain values in the linear regime reach $\sim 100$ at voltages close to $U_{\mathrm{br}}=32.9 \mathrm{~V}$. Stable spectral responsivity in the $980-1600 \mathrm{~nm}$ range at gain $=1$ is demonstrated.

InGaAs/InP single-photon avalanche photodiode (SPAD) with a triple-step diffusion morphology is designed and fabricated. The avalanche probability distribution evolves from a toroidal shape to a Gaussian-like shape as compared with the conventional double-step diffusion. Free-running measurements indicate that the photon detection efficiency of the triple-step SPAD increases from 3.4% to 11% in comparison with a double-step SPAD with the same thickness of the avalanche region and under the same conditions. Meanwhile, the dark count rate (DCR) and the afterpulsing probability (APP) are also decreased from 820 to 25 kHz and from 80% to 43% under a hold-off time of $8~\mu $ s, respectively. Consistently higher activation energies of both the dark current and the DCR are obtained for the triple-step SPAD, tentatively attributed to the evolvement of the dominant source of dark carriers from the thermal generation in the InGaAs absorber to the trap-assisted tunneling in the InP multiplier. Theoretical simulations indicate a faster detrapping time of carriers within the avalanche region accounts for the reduced APP for the triple-step SPAD with a higher peak E-field.

This work reports high-performance homojunction gallium nitride (GaN) p-i-n (PIN) avalanche photodiodes (APDs) grown on a low-defect GaN substrate and fabricated with an ~1.8° shallow-bevel-mesa edge termination. High-quality p-i-n GaN epitaxial layers were grown using metalorganic chemical vapor deposition (MOCVD), and the device edge termination was achieved by multistep pseudo gray-scale lithography followed by photoresist reflow and dry etching of the bevel mesa. Fabricated GaN APDs showed an ultralow dark current density <inline-formula> <tex-math notation="LaTeX">$\lt 10^{-{9}}$ </tex-math></inline-formula> A/cm2 in the low-mid reverse bias voltage region prior to avalanche breakdown and achieved a current-limited photocurrent gain of <inline-formula> <tex-math notation="LaTeX">$\gt 10^{{7}}$ </tex-math></inline-formula> under deep-ultraviolet (DUV) illumination at <inline-formula> <tex-math notation="LaTeX">$\lambda =280$ </tex-math></inline-formula> nm and a reverse bias −107 V. The total current density without illumination was in the order of <inline-formula> <tex-math notation="LaTeX">$10^{-{5}}$ </tex-math></inline-formula> A/cm2 at the onset of avalanche breakdown. The avalanche breakdown characteristic was confirmed by temperature-dependent J–V studies, with a derived positive temperature coefficient of 0.02 V/K for the breakdown voltage (BV). The analysis of the temperature-dependent reverse-bias characteristics indicated that the reverse leakage current components before avalanche could be attributed to trap-assisted tunneling (TAT) and phonon-assisted tunneling (PAT) processes.

We present a high-performance InGaAs/Si avalanche photodiode (APD) enabled by heterogeneous bonding using a microcrystalline Ge interlayer. The bonding interface achieves void-free, oxide-free, and robust III–V/Si integration, minimizing interface defects and thermal stress. The APD exhibits responsivities of 42 A/W and 33.8 A/W with gains of 24.06 and 38.32 at 1310 and 1550 nm, respectively, outperforming Ge/Si and InGaAs devices. Notably, an optically tunable punch-through voltage is observed, attributed to space-charge modulation caused by hole trapping in potential wells at the bonded interface. The device maintains stable photoresponse up to 470 K. These results highlight its potential for LIDAR, thermal sensing, and integrated photonics.

Geiger-mode InGaAsP/InP single photon avalanche photodiode (SPAD) with a low dark count rate (DCR) of 870 Hz at a photon detection efficiency (PDE) of 20% at 1064 nm is achieved for a 40 micron diameter device at −30 °C. Extensively optimized and accurately controlled shallow/deep two-step pn junction and doping profiles are identified to play decisive roles for the performance improvement. While a state-of-the-art specific detectivity of 1.4×1014 cm·Hz1/2/W is realized for the optimized SPAD, a temperature coefficient of the breakdown voltage (Vbr) of 139 mV/K, a dark current of 200 pA at 90%Vbr and a timing jitter of 280 ps at 20% PDE are also simultaneously attained. Thermal activation energies of approximate 0.5 eV are observed for both the dark current and the DCR at 253–293 K, indicates the dominant source of dark carriers is the mid-gap defect trapping states-related tunneling in the InGaAsP absorber.

Low Gain Avalanche Detectors (LGADs) provide high time resolution at moderate charge gain, making them essential for high-energy physics experiments, such as those at the High Luminosity Large Hadron Collider. However, their performance is significantly impacted by radiation induced defects, particularly at high hadron fluences. This study is devoted to the characterization of degradation mechanisms in LGADs irradiated with 24 GeV/c protons at fluences ranging from 1012 to 1016 cm-2. Carrier lifetime (τR ) variations examined using the microwave probed photoconductivity transients revealed a significant reduction of τR from >10 μs in non-irradiated samples to <1 ns at the highest fluence irradiated sensors, indicating increased densities of defects acting as deep-level recombination centers. Photoionization and deep level transient spectroscopy techniques have been employed to identify radiation induced defects. The impact of these defects on the electric field distribution and internal gain in LGADs was comprehensively analyzed using Synopsys TCAD Sentaurus and MATLAB simulations. The results indicate a substantial reduction in gain from 26 for non-irradiated sensors to a negligible its value for 1016 cm-2 fluence irradiated LGADs due to a simultaneous reduction of effective doping concentration, decreased τR and enhanced trapping. The study provides a versatile methodology for correlating electrical and spectroscopic measurements with defect characterization, offering valuable insights for optimizing LGAD design in radiation-rich environments.

A back-illuminated heterostructure AlGaN avalanche photodiode (APD) was fabricated with a separate absorption and multiplication (SAM) structure. The SAM structure is able to modulate the electric field distribution of the photodetector and induce a single carrier to trigger an avalanche event. The fabricated p-i-n-i-n APD exhibited a superior maximum gain of 1.8 × 105 at 70 V and distinct solar-blind responsivity peak at 280 nm. However, before the avalanche occurs, the SAM APD needs to be reached through for facilitating carrier transport. By investigating the capacitance characteristics of the SAM APD, the reach-through behavior was directly observed. The capacitance of the detector demonstrated evident declining trends with the applied voltage in the range of 18 to 24 V at different frequencies. The simulated electric field and energy band also revealed that the absorption region was initially reached through at 18 V reverse bias, corresponding to the depletion of n-type interlayer into the absorption region. Meanwhile, there were large differences in capacitances between low and high frequencies, which indicated the effects of impurity and defect states. These findings explicitly reveal the reach-through mechanism of the SAM APD, which is beneficial to the better understanding of device physics and further APD design.

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Near infrared single photon detection using an InGaAs/InP avalanche photodiode(APD) operated with a bipolar rectangular gating signal was reported. The use of the bipolar gating pulses enabled us to operate the APD well below the breakdown voltage during the gate-off time. As a result, it permits to decrease the lifetime of the trapped carriers, and then reduces the after-pulse noise of the detector. At a repetition rate of 200 MHz, the after-pulse probability is 8.2% less than conventional gating signal detection.

In applications such as LiDAR, quantum communication, biomedical imaging, and telecommunications, avalanche photodiodes (APDs) are a main component enabling highly sensitive optical detection. This review, with a particular focus on important architectures such as RAPD, SAM, SACM, and SAGCM, examines their development from early bulk semiconductors to modern heterostructures and new two-dimensional (2D) materials. The impact of structural innovations on the enhancement, noise, and bandwidth optimization for photon-trapping nanostructures, multiple quantum wells, and superlattices is evaluated. An analysis of the remaining problems related to material quality, lattice matching, manufacturing accuracy, and smooth integration of CMOS is conducted. In conclusion, the prospects are discussed, with particular attention given to dual-gain architectures, silicon photonics integration, 2D platforms, and AI-assisted TCAD methods for rapid defect-aware device optimization. This article presents a consolidated roadmap for improving the performance of APDs in next-generation optoelectronic systems.

PureB single-photon avalanche diodes (SPADs) integrate ultra-shallow p⁺n junctions formed by nanometer-thin boronlayer deposition, providing high sensitivity to shallow-penetration photons and particles. PureB SPADs have achieved low dark count rates below 1Hz/μm2 and were designed with an implicit guard ring configuration to increase the fill factor. The fabricated devices include SPADs both with and without an n+ buried layer, where contamination during processing was identified as a source of bulk defects in the silicon. In this work, we present a spatial responsivity analysis of PureB SPADs using a focused-laser scanning optical-setup. The setup was calibrated on conventional PureB photodiodes using continuous-wave lasers at 520nm and 638nm, and pulsed lasers at 660nm and 1060nm, with spot sizes down to 2μm as determined by using the knife-edge method. High-resolution spatial scanning of PureB SPADs identified regions of decreased responsivity across the SPAD entrance window that were attributed to the presence of bulk defects and lower carrier lifetimes resulting from device processing. Additionally, line scans and two-dimensional maps revealed increased responsivity before onset of multiplication localized at the diode perimeter related to spreading of the depletion region and diffusion of photogenerated carriers from the quasi-neutral region. Optoelectrical line-scan simulations of the SPAD responsivity were performed using technology computer aided design (TCAD) to analyze the impact of perimeter carrier collection, defects and lifetime on spatial responsivity.

This article presents a comprehensive evaluation of the separated absorption, graded, charge, and multiplication (SAGCM) avalanche photodiodes (APDs) through both numerical calculations and experimental measurements. A total of 135 device configurations were designed and tested to investigate the effects of multiplication width (MW), attached guard ring (AGR) thickness, floating guard ring (FGR) spacing and thickness, and the number of attached FGRs (AFGRs) on device performance. Optimization was carried out based on breakdown and punchthrough voltages with respect to gain. The impact of MW was examined across a range from 0.3 to $0.9~\mu $ m, with corresponding evaluations of electric field profiles, breakdown voltage, and punchthrough voltage. To isolate the influence of the AGR and FGR structures, the subsequent analyses were carried out with a fixed MW of $0.3~\mu $ m. Four different AGR thicknesses were experimentally tested to determine the optimal value. Additionally, three FGR spacings and three FGR thicknesses were evaluated in combination with each AGR configuration, and the impact of varying the number of FGRs was also examined. As a result of these optimizations, the device breakdown voltage was significantly improved from 43.9 to 57.6 V while maintaining a gain of 10.

Silicon avalanche photodiodes (Si APDs) serve as core devices for low-light detection in the visible and near-infrared wavelength range. Currently, driven by the advanced complementary metal oxide semiconductor (CMOS) technology, the main junction of APDs, where the avalanche occurs, typically relies on ion implantation, yielding a relatively steep electric field profile, which impose constraints on device performance. This paper presents a systematic investigation into the design, simulation, and characterization of Si APDs based on an n-type epitaxial (n-epi) process. This innovative process enables the engineering of a tailored electric field profile with a broader peak, addressing the limitations of conventional ion-implanted structures. Systematic simulations were performed to analyze the impacts of critical device parameters, including charge layer concentration, multiplication layer thickness, and guard ring structure. Guided by the simulation results, prototype silicon APDs incorporating a lightly doped p-type guard ring were fabricated. Experimental characterization reveals that the devices exhibit a low breakdown voltage of 12.8 V and a maximum gain exceeding 1000, leading to reduced power consumption. This design approach demonstrates significant potential for Si APDs through the epitaxial approach.

For the first time, we proposed and investigated a field-plate (FP) integrated mesa-type InGaAs/InP avalanche photodiode (APD). The shallow-mesa structure helps to suppress the surface effect. At the same time, the FP can minimize the electric field crowding at the mesa edges to avoid the pre-mature breakdown, which could be realized via simple fabrication processes. The impact of FP's length, thickness, and material are considered and investigated by the Sentaurus TCAD simulation, where the effectiveness of our structure is confirmed.

We developed a miniaturized high-sensitivity single-photon avalanche diode (SPAD) device based on 180 nm bipolar complementary metal–oxide–semiconductor double-diffused metal–oxide–semiconductor technology and investigated the effect of a deep virtual guard ring (VGR) on device performance. To mitigate the degradation in photon detection efficiency (PDE) and dark count rate (DCR) induced by device scaling, we innovatively implemented a P-type implant/high-voltage n-well SPAD structure. This configuration deepens and widens the multiplication region to broaden the spectral response, while the specialized adoption of the P-type epitaxial VGR technology suppresses premature edge breakdown and reduces dark noise. Furthermore, a unique layout was devised to maximize the photosensitive area and increase the fill factor of the device. Through technology computer-aided design simulations, the effect of the guard ring width on the electric field distribution inside the device was systematically studied. Experimental results demonstrate that the fill factor of the device reaches 31.5% when the pitch is scaled down to 8.5 μm. The novel device achieves a high peak PDE of 24% at 555 nm and an ultralow DCR of 0.41 cps⋅μm−2 at 5 V excess bias voltage.

This study aims to investigate the effectiveness of different guard ring (GR) structures in suppressing edge breakdown issues in InGaAs/InP planar avalanche photodiodes (APDs) with a thicker multiplication layer design through highly realistic simulations. Based on the simulation results of the limitations of conventional GR structures, we introduce a novel concept known as attached step GRs (ASGR). Through this feasible diffusion structure, edge breakdown has been improved, with a 23% increase in breakdown voltage compared to traditional structures. The higher electric field is effectively confined within the central region of the multiplication region, while also achieving a threefold increase in current gain and quantum efficiency (QE) enhancement of over 20%.

We present robust pixel design methodologies for a vertical avalanche photodiode-based CMOS image sensor, taking account of three critical practical factors: (i) “guard-ring-free” pixel isolation layout, (ii) device characteristics “insensitive” to applied voltage and temperature, and (iii) stable operation subject to intense light exposure. The “guard-ring-free” pixel design is established by resolving the tradeoff relationship between electric field concentration and pixel isolation. The effectiveness of the optimization strategy is validated both by simulation and experiment. To realize insensitivity to voltage and temperature variations, a global feedback resistor is shown to effectively suppress variations in device characteristics such as photon detection efficiency and dark count rate. An in-pixel overflow transistor is also introduced to enhance the resistance to strong illumination. The robustness of the fabricated VAPD-CIS is verified by characterization of 122 different chips and through a high-temperature and intense-light-illumination operation test with 5 chips, conducted at 125 °C for 1000 h subject to 940 nm light exposure equivalent to 10 kLux.

This work investigates the edge breakdown issue in InGaAs/InP planar avalanche photodiodes. We have demonstrated a novel attached step guard rings concept can prevent edge breakdown by suppressing the edge electric field up to 10.5 %. Furthermore, we improve the noise, current performance.

We report on the design of an attached guard ring (AGR) and a floating guard ring (FGR) in a planar separate absorption, grading, charge, and multiplication In0.53Ga0.47As/InP avalanche photodiode to prevent premature edge breakdowns. The depths of the two Zn diffusions were utilized to manipulate the guard ring structures. Results from TCAD simulation indicate that the optimal AGR diffusion depth is right at the turning point where the breakdown current shifts from the edge of active region to the AGR region. The devices with optimal AGR depth contain significantly higher breakdown voltages than those of devices either with shallower—or without any— AGR. For the FGR design, a series of devices with different spacings between AGR and FGR and different FGR opening widths for diffusion were fabricated and characterized. We show that when the spacing is longer than the critical value, the breakdown voltage can increase ~1.5 V higher than those of the APD devices without FGR. In addition, the wider the FGR opening width, the higher the breakdown voltage. TCAD simulations were also performed to study the effect of FGR, but showed less pronounced improvements, which could be due the discrepancy between the calculated and experimental diffusion profile.

Avalanche photodiodes (APDs) based on InGaAs/InP are pivotal for applications in low-light detection, yet their performance is often hindered by edge breakdown and high dark currents. This study systematically optimizes guard ring structures to address these challenges, focusing on attached guard rings (AGRs) and floating guard rings (FGRs) through a synergistic approach combining simulation-guided design, fabrication, and experimental validation. We analyze the impact of Zn diffusion depth, AGR/FGR geometries, and electric field distribution on device performance. Experimental results demonstrate that optimized AGR structures reduce dark currents by 70% and enhance quantum efficiency (QE) by 43%, while FGR structures achieve an order-of-magnitude reduction in dark current and a 90% QE improvement compared to non-guarded devices. The breakdown voltage increases by 2.5 V (AGR) and 4 V (FGR), leading to enhanced gain. These advancements highlight the critical role of guard ring optimization in effectively mitigating edge breakdown, offering a pathway to high-sensitivity InGaAs/InP APDs for photon detection technologies.

Premature edge breakdown (PEB) remains a critical challenge in the design of single-photon avalanche diodes (SPADs) in complementary metal-oxide-semiconductor (CMOS) technologies. To mitigate this issue, guard ring (GR) structures must be carefully designed to reduce the electric field at the ${\boldsymbol{p}}$-${\boldsymbol{n}}$ junction edges without compromising other key performance metrics such as dark count rate (DCR) and photon detection efficiency (PDE). We investigate and compare different GR structures in CMOS SPADs through literature review and numerical simulations. Four widely used GR structures, including shallow trench isolation, diffusion GR, virtual GR and poly gate GR, are explored, together with hybrid and extended GR-related strategies. Furthermore, finite-element simulations using COMSOL Multiphysics are performed to evaluate the effectiveness of these GR structures in suppressing PEB and to compare the electric-field redistribution and avalanche-triggering tendencies of representative GR structures, while their impacts on DCR, PDE, and fill factor are critically discussed based on reported results. Based on the comparative analysis of different GR structures, future research directions are proposed for optimizing GR designs in CMOS SPADs to meet the required performance of emerging applications. The investigation outcomes presented in this work can serve as practical design guidelines for the GR structures in CMOS SPADs.

In this letter, we report a high-uniformity <inline-formula> <tex-math notation="LaTeX">$2\times 128$ </tex-math></inline-formula> silicon avalanche photodiode linear array for 3D imaging. The <inline-formula> <tex-math notation="LaTeX">$100~\mu \text{m}$ </tex-math></inline-formula> diameter, <inline-formula> <tex-math notation="LaTeX">$50~\mu \text{m}$ </tex-math></inline-formula> gap pixels incorporate floated guard ring and edge implantation to prevent premature breakdown. Despite the large scale, breakdown voltage uniformity across all 256 pixels exceeds 98.8%. At room temperature, pixels show 0.55 A/W peak responsivity at gain =1 (80% external quantum efficiency at 875 nm) and maximum gain exceeds 550 at 95% breakdown voltage. The array exhibits a 1.6 V deviation in breakdown voltages from 122.8~126 V across pixels, indicating a high uniformity larger than 98.8%. Dark current remains below 60 pA at gain =1 and 300 pA at 90% breakdown voltage per pixel. The capacitance is below 0.4 pF near avalanche. Furthermore, we measured the dark current-voltage characteristic at various temperatures, and a consistently low dark current, at approximately 10 nA, was obtained at a temperature up to 100 °C. These results represent a significant advance for silicon linear arrays in 3D imaging.

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Abstract. The use of a physical guard ring in CMOS single-photon avalanche diodes (SPADs) based on n  +  /(deep)p-well and p  +  /(deep)n-well structures is a common solution to control the electric field of the SPADs periphery and prevent the premature lateral breakdown. However, this leads to a decrease of the detection efficiency, i.e., the fill-factor, especially when the SPADs size is reduced. Our paper presents an experimental and simulation study on replacing the physical guard ring by a virtual guard ring to improve the fill-factor and the scalability of a n  +    /  p-well SPAD implemented in 0.35-μm pin-photodiode CMOS technology. Accordingly, the optimization of the virtual guard ring and its superiority at downscaling are discussed, and the SPAD scalability in size with respect to the fill-factor is quantified in this technology.

Fluorescence optical fiber temperature sensors have found widespread use in harsh environments with electromagnetic interference, high voltages, flammability, and combustibility due to their excellent insulating properties. However, conventional fluorescence detection systems are constructed from discrete photodiodes and other front-end circuit chips, which cause bulky size, inferior detection efficiency, and degraded signal-to-noise performance. To address these issues, an integrated optical front-end circuit for fluorescence detection was proposed. The front-end circuit monolithically integrated a ring-gate-isolated photodiode (RGI-PD) device, a transimpedance amplifier (TIA), and a bandgap reference (BGR) circuit. The RGI-PD enabled the detection of the fluorescence afterglow signals, while the TIA circuit converted the photocurrent generated by the RGI-PD into a measurable photovoltage output. The RGI-PD utilized a P-well guard ring structure to prevent edge breakdown by isolating the avalanche region from the shallow trench. The dummy ring-gate created an inverted pyramid hole profile, focusing the electric field on the planar junction to enhance photodetection, which reduced trapping effects and dark counts. The proposed front-end circuit was fabricated using a standard $0.18~\mu \text{m}$ bipolar CMOS DMOS (BCD) process. The measurement results demonstrated that the avalanche breakdown voltage (BV) of the RGI-PD was 13.05 V. The front-end circuit achieved a responsivity of 17.29 A/W at 500 nm wavelength, under a 13.88 V reverse bias voltage applied on the RGI-PD. Moreover, the front-end’s dark voltage measured 0.908 V, with an optimal temperature coefficient (TC) of 41.01 ppm/°C within the temperature range of −40 °C to 85 °C. The proposed front-end circuit was suitable for fluorescence fiber temperature sensing applications.

In this work, we report a low-noise, high-gain 2 × 128 silicon avalanche photodiode (Si-APD) linear array for LiDAR sensing. Each pixel has a diameter of 100 μ m with a pitch of 180 μ m. A shallow etching process is employed on the APD to suppress premature edge breakdown, obviating the requirement for an additional guard ring structure. Isolation trenches implanted by boron effectively suppress crosstalk between pixels. At room temperature and unity gain, the device exhibits a peak responsivity of 0.51 A/W at 735 nm, corresponding to a peak external quantum efficiency (EQE) of 88.3% at 695 nm. The spectral response spans approximately 300 – 1050 nm. Under the operating bias (95% of the breakdown voltage, 120 V), the typical gain exceeds 100, and the maximum gain surpasses 10 6 near breakdown. The dark current remains below 550 pA, and the capacitance is lower than 0.4 pF. The excess noise factor is less than 3.5, and the ionization coefficient ratio kis below 0.02 at a gain of 80. These excellent results represent a significant advance in silicon linear arrays for 3D imaging applications.

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Single-photon avalanche diodes (SPADs) are key photodetectors for low-light and photon-counting imaging applications. However, their performance is often limited by dark count rate (DCR), which is strongly affected by junction structure, peripheral electric-field distribution, and multiplication-region size. This paper presents a measurement-based analysis of SPAD pixels with different guard-ring configurations fabricated in a TSMC 180-nm CMOS process. STI-isolated SPADs without a dedicated guard ring and p-well guard-ring-assisted SPADs are implemented with different multiplication-region diameters and compared under the same excess-bias range and a fixed dead-time condition of 200ns. The measured results show that the STI-isolated SPADs exhibit a rapid DCR increase as the excess bias voltage and multiplication-region diameter increase, whereas the p-well guard-ring-assisted SPADs effectively suppress this increase. The area-normalized DCR comparison further confirms that peripheral electric-field control is critical for reducing dark-count generation. Among the fabricated devices, the Type 4 p-well guard-ring-assisted SPAD with a 5- $\mu $ m multiplication-region diameter achieves the most favorable overall performance, with a peak photon detection probability of 20.91% at 550nm and an afterpulsing probability of 0.06%. These results provide practical design guidelines for selecting guard-ring structures and multiplication-region sizes in CMOS-compatible SPAD pixels for low-noise photon-counting applications.

In this study, we experimentally determined the impact ionization coefficients of GaN using p–i–n avalanche photodiodes with a hybrid mesa structure. Single-carrier-type initiation was achieved using two optical-window configurations based on the same hybrid-mesa p–i–n architecture, enabling p-side illumination for electron injection and n-side illumination for hole injection. The electron and hole impact ionization coefficients were obtained as α (E) = 2.22 × 106 exp(−1.64 × 107/E) cm−1 and β (E) = 1.58 × 105 exp(−3.29 × 106/E) cm−1, respectively, over the electric field range from 2.2 to 2.8 MV/cm. The results show that the impact ionization coefficient of holes is substantially greater than that of electrons (β/α > 10 at 2.5 MV/cm), indicating the advantage of hole-initiated avalanche multiplication for GaN-based avalanche photodiodes.

The avalanche photodiode is a highly sensitive photon detector with wide applications in optical communication and single photon detection. ZnO is a promising wide band gap material to realize a UV avalanche photodiode (APD). However, the lack of p-type doping, the strong self-compensation effect, and the scarcity of data on the ionization coefficients restrain the development and application of ZnO APD. Furthermore, ZnO APD has been seldom reported before. In this work, we employed a p-Si/i-ZnO/n-AZO structure to successfully realize electron avalanche multiplication. Based on this structure, we investigated the band structure, field profile, Current–Voltage (I-V) characteristics, and avalanche gain. To examine the influence of the width of the i-ZnO layer on the performance, we changed the i-ZnO layer thickness to 250, 500, and 750 nm. The measured breakdown voltages agree well with the corresponding threshold electric field strengths that we calculated. The agreement between the experimental data and calculated results supports our analysis. Finally, we provide data on the impact ionization coefficients of electrons for ZnO along the (001) direction, which is of great significance in designing high-performance low excess noise ZnO APD. Our work lays a foundation to realize a high-performance ZnO-based avalanche device.

We propose a broadband noise test method (10 Hz–1 MHz) using a direct power method to measure the excess noise of InGaAs/InP avalanche photodiodes (APDs) with a separate absorption, grading, charge, and multiplication structure. By this means, the impact ionization coefficient ratio (the k value) can be accurately determined. Compared with previous studies, this method can distinguish between low-frequency noise and excess noise, so for an appropriate high frequency spectral range, the excess noise can be analyzed without mixing in other noise information. Three different APDs fabricated in-house with different diameters (12, 25, and 60 µm) were investigated using the above-mentioned method under temperatures varying from −10 to −40 °C. Our findings showed that the k value of the APDs decreased as the temperature decreased. When the temperature decreased to −40 °C, the k value of the 12, 25, and 60 µm diameter diodes was as low as 0.1, 0.3, and 0.2, respectively. The measurement results are consistent with our device design and not only provide useful information for the future selection of device materials and structures but also demonstrate the feasibility of the broadband noise measurement method in the accurate determination of the k value. It indicates that low excess noise can be achieved by utilizing the temperature dependence of k.

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Recently, a method to extract temperature coefficients of impact ionization (II) from the linear and quadratic temperature coefficients of avalanche voltage was successfully applied for 4H-SiC devices. We apply the same method here to Silicon by first providing new data for linear and quadratic temperature coefficients of avalanche voltages and using the method to derive new temperature coefficients for four different models of II coefficients.

A valanche multiplication characteristics in GaN p-n junction diodes (PNDs) under high reverse bias conditions were investigated. The GaN-on-GaN PNDs with double-side-depleted shallow bevel termination, which showed low reverse leakage current and excellent avalanche capability, were used for the measurements. Under sub-bandgap light illumination, the photocurrents induced by Franz-Keldysh (FK) effect, which can be well reproduced by the theoretical calculations of the optical absorption, and their avalanche multiplications were observed. The multiplication factors were extracted as the ratios of the experimental photocurrents to the calculated FK-induced photocurrent. Under an assumption of equal impact ionization coefficients of electrons and holes, the electric-field dependence of an impact ionization coefficient in GaN were estimated.

This abstract presents an experimental study on the measurement of the hole impact ionization coefficient and saturation velocity in GaN. A novel p-n structure with a buried p-GaN was designed and demonstrated to have avalanche capability. Ultraviolet generated holes were swept into the high electric field region when the p-n diode was reversely biased and triggered the hole-initiated impact ionization multiplication. The measured hole saturation velocity is $7\times 10^{6}$ cm/s, and the impact ionization coefficient is $\boldsymbol{\beta}(\boldsymbol{E})=4.39\times 10^{6}\mathbf{exp}(-1.8\times 10^{7}/\boldsymbol{E})$.

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We use an ensemble Monte Carlo transport approach to calculate and compare the impact ionization and avalanche photodiode excess noise characteristics in three materials—a band-engineered InAlAs/InAsSb type-II superlattice, bulk InAs, and HgCdTe—all with an identical bandgap of 370 meV at 250 K. The electronic band structures and energy–momentum conservation conditions are used to calculate the impact ionization rates, carrier histories, multiplication gains, and excess noise characteristics. The calculated impact ionization coefficients and excess noise factors indicate a single carrier species multiplication in all three materials under low applied electric fields. We find the ratio of impact ionization coefficients to be k=7×10−4 for InAs and 3×10−4 for HgCdTe under an applied field of 50 kV/cm, and the superlattice to be k<10−6 at fields up to 400 kV/cm. The bulk materials experience avalanche breakdown as the applied field increases, transitioning to Geiger mode behavior at gains above 103 for InAs and 104 for HgCdTe. However, this breakdown is absent from the superlattice at the highest fields considered in this study due to hole confinement, indicating superior performance compared to the bulk materials. Our results demonstrate the role of superlattice band engineering in designing quality avalanche photodiode materials.

This paper proposes a 6H-materials silicon carbide (SiC)/gallium nitride (GaN) heterogeneous p-n structure to replace the GaN homogenous p-n junction to manufacture an impact-ionization-avalanche-transit-time (IMPATT) diode, and the performance of this 6H-SiC/GaN heterojunction single-drift-region (SDR) IMPATT diode is simulated at frequencies above 100 GHz. The performance parameters of the studied device were simulated and compared with the conventional GaN p-n IMPATT diode. The results show that the p-SiC/n-GaN IMPATT performance is significantly improved, and this is reflected in the enhanced characteristics in terms of operating frequency, rf power, and dc-rf conversion efficiency by the two mechanisms. One such characteristic that the new structure has an excessive avalanche injection of electrons in the p-type SiC region owing to the ionization characteristics of the SiC material, while another is a lower electric field distribution in the drift region, which can induce a higher electron velocity and larger current in the structure. The work provides a reference to obtain a deeper understanding of the mechanism and design of IMPATT devices based on wide-bandgap semiconductor materials.

Impact ionization coefficients play a critical role in semiconductors. In addition to silicon, silicon carbide and gallium nitride are important semiconductors that are being seen more as mainstream semiconductor technologies. As a reflection of the maturity of these semiconductors, predictive modeling has become essential to device and circuit designers, and impact ionization coefficients play a key role here. Recently, several studies have measured impact ionization coefficients. We dedicated the first part of our study to comparing three experimental methods to estimate impact ionization coefficients in GaN, which are all based on photomultiplication but feature characteristic differences. The first method inserts an InGaN hole-injection layer, the accuracy of which is challenged by the dominance of ionization in InGaN, leading to possible overestimation of the coefficients. The second method utilizes the Franz–Keldysh effect for hole injection but not for electrons, where the mixed injection of induced carriers would require a margin of error. The third method uses complementary p–n and n–p structures that have been at the basis of this estimation in Si and SiC and leans on the assumption of a constant electric field, and any deviation would require a margin of error. In the second part of our study, we evaluated the models using recent experimental data from diodes demonstrating avalanche breakdown.

Wide bandgap semiconductors, such as gallium nitride (GaN) and silicon carbide (SiC), have bandgap energies larger than 3 eV with high breakdown electric fields, showing the advantage on powerful IMPATT diodes. SiC IMPATT diodes have been successfully demonstrated and shown excellent performances in X-band applications [1] , [2] . Although a few theoretical studies have shown the great potential of GaN for powerful IMPATT diodes [3] , [4] , no experimental study has been reported so far. Taking advantage of the single crystalline GaN substrates enabling high quality GaN films, avalanche capability has been demonstrated [5] – [9] . In this study, we demonstrated a GaN-based IMPATT diode experimentally by using a n-i-p epitaxial structure grown on a bulk GaN substrate.

The presence of large bismuth (Bi) atoms has been shown to increase the spin–orbit splitting energy in bulk GaAsBi, reducing the hole ionization coefficient (β) and thereby reducing the excess noise seen in avalanche photodiodes. In this study, we show that even very thin layers of GaAsBi introduced as quantum wells (QWs) in a GaAs matrix exhibit a significant reduction of β while leaving the electron ionization coefficient, α, largely unchanged. The optical and avalanche multiplication properties of a series of GaAsBi/GaAs multiple quantum well (MQW) p-i-n structures with nominally 5 nm thick, 4.4% Bi GaAsBi QWs, varying from 5 to 63 periods and corresponding barrier widths of 101 to 4 nm were investigated. From photoluminescence, ω-2θ X-ray diffraction, and cross section transmission electron microscopy measurements, the material was found to be of high quality despite the strain introduced by the Bi in all except the samples with 54 and 63 QW periods. Photomultiplication measurements undertaken with different wavelengths showed that α in these MQW structures did not change appreciably with the number of QWs; however, β decreased significantly, especially at lower values, the noise factor, F, is reduced by 58% to 3.5 at a multiplication of 10, compared to a similar thickness bulk GaAs structure without any Bi. This result suggests that Bi-containing QWs could be introduced into the avalanching regions of APDs as a way of reducing their excess noise.

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In this article, three polytypes of p-(6H, 4H, 3C)SiC and n-GaN heterojunction single-drift (SDR) and double-drift (DDR) impact-ionization-avalanche-transit-time (IMPATT) diodes are studied. We conduct the numerical simulations of the direct current (DC), radio frequency (RF), and noise characteristics of IMPATT diodes. The results show that (6H)SiC/GaN IMPATT diodes have the optimum RF characteristics. Among them, the RF power density of (6H)SiC/GaN DDR IMPATT diode can reach 2.23 MW/cm2. The DC-RF conversion efficiency of (6H)SiC/GaN SDR IMPATT diode can reach 23.4%. Their noise performances are being examined in the meantime. The (3C)SiC/GaN IMPATT has better noise characteristics in the SDR structure, while (4H)SiC/GaN IMPATT has better noise characteristics in the DDR structure. This study provides a reference for the design and fabrication of IMPATT diodes.

Sustainable avalanche operation was demonstrated and investigated on lateral E-mode GaN HEMT devices with sub-micrometer gate length. Through an extensive analysis: a) we demonstrated that sustainable avalanche operation is made possible by the presence of a subthreshold drain-source leakage, that initiates impact ionization; b) this process clamps the drain voltage to values lower than the dielectric breakdown voltage, thus preventing the catastrophic failure of the devices; c) avalanche operation is sustainable, and the related voltage strongly depends on the device geometry; d) spectrally resolved electroluminescence measurements demonstrate the presence of band-to-band luminescence, ascribed to recombination of holes, generated by impact ionization during the process. Finally, e) the positive temperature coefficient of avalanche voltage has been demonstrated. Support to the interpretation was obtained based on TCAD simulations.

We report the GaN-based diode avalanche shaper (DAS) employing ultra-small-angle bevel junction termination extension and slanted field plate hybrid edge terminations. Compared with Si and GaAs DASs, the thinner and lightly doped drift layer maintains a uniformly high electric field prior to avalanche, enabling full-region avalanche without impact ionization-wave propagation and yielding over two orders of magnitude higher current density. The GaN DAS delivers a >2.5 kV peak output voltage with a 93 ps rise time and achieves a 4-times bandwidth enhancement from 1.6 to 6.3 GHz. A record peak output power density of 1.68 GW/cm2 is obtained, exceeding those of Si and GaAs DASs by more than 100 times of magnitude and that of SiC DASs by a factor of 27. These results underscore GaN as a leading wide-bandgap platform for picosecond-class ultrafast DASs and compact, ultra-wideband, high-repetition-rate pulsed power systems.

Accurate modeling of impact ionization coefficients is a critical requirement for the design and optimization of avalanche photodiodes (APDs) and ultraviolet single-photon detectors. In this work, hole impact ionization coefficients in GaN-based structures from the laboratory results presented in the references extracted and systematically analyzed using two widely adopted analytical models, namely the standard Okuto-Crowell and Selberherr models. The ionization data are obtained from experimentally reported gain characteristics and by solving the corresponding equations. The model parameters are determined via an iterative optimization process aimed at minimizing the mean squared error within the logarithmic scale. The performance of each model is quantitatively assessed based on a specified error criterion. The results demonstrate that while the Okuto-Crowell model provides a simple and physically intuitive description, its limited parameter set restricts fitting accuracy. In contrast, the Selberherr model exhibits significantly improved agreement with experimental data, achieving a 33.66% enhancement in fitting performance. This improvement is firstly due to the increased number of fitting parameters, which provides greater flexibility for capturing the complex behavior of hole impact ionization under high electric fields. The extracted parameters and comparative analysis provide valuable insights for accurate ionization modeling and can serve as a reliable result for the design of high-performance GaN-based APDs and deep-ultraviolet single-photon detection systems.

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Based on results from the Silvaco Atlas device simulation software, a separate absorption grading charge multiplication InGaAs/InP avalanche photodiode has been modeled. The Shockley-Read-Hall current, avalanche amplification current, trap-assisted tunneling current, and band-to-band direct tunneling current are combined and considered as the dark current. Individual components of the dark current have been obtained separately through numerical simulation. Due to the multiplication effect, the influence of the multiplication layer on the dark current components has been studied. The simulation results are analyzed based on semiconductor physics knowledge. The conclusions presented provide some theoretical guidance for the optimum design of avalanche photodiodes.

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Short-wave infrared (SWIR) avalanche photodiodes (APDs) are important for LiDAR, free-space optical communication, and low-light imaging. Colloidal quantum dots (CQDs) offer a solution-processable, silicon-compatible SWIR platform, but conventional CQD p-i-n APDs couple photon absorption and avalanche multiplication in the same narrow-bandgap layer, causing severe dark-current growth under high reverse bias. Here, we demonstrate a CQD/i-ZnO APD based on a separate-absorption-charge-multiplication (SACM) architecture. By relocating the high-field multiplication region from the narrow-bandgap CQD absorber to wide-bandgap i-ZnO, this design suppresses tunneling-induced dark current while retaining avalanche multiplication. The optimized device achieves a gain-normalized dark current density of 4.86 × 10-7 A cm-2, the lowest reported among CQD photodetectors with internal gain, and a specific detectivity of 1.15 × 1012 Jones. These results establish SACM field engineering as an effective route toward low-dark-current CQD-based SWIR APDs.

Currently, colloidal quantum dots (CQDs) photodetectors have shown significant advancement in the field of infrared photodetection. However, the immature analysis of dark current components hinders the realization of higher performance quantum dots optoelectrical devices. In this study, based on a PbS CQD photodetector, we employ a conventional dark current model of infrared photodetectors to analyze the dark current components of the device, yielding fitting results highly consistent with experimental observations. Our findings indicate that with increasing reverse bias, the dominant dark current components of the PbS CQD photodetector shift from diffusion (Diff) current, generation-recombination (G-R) current, and shunt (sh) current to trap-assisted tunneling (TAT) current. The band diagrams, recombination rates, carrier density distributions, and electric field intensity maps under different biases are further simulated, of which the theoretical results confirm that current components transition is attributed to the abundance of defects in quantum dot materials, leading to tunneling at the interface between the SnO2 layer and PbS-I layer under high bias conditions. Our work contributes to providing insight and direction for optimizing the CQD photodetector performances.

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We fabricated AlGaN solar-blind avalanche photodiodes (APDs) that were based on separate absorption and multiplication (SAM) structures. It was determined experimentally that the dark current in these APDs is rapidly enhanced when the applied voltage exceeds 52 V. Theoretical analyses demonstrated that the breakdown voltage at 52 V is mainly related to the local trap-assisted tunneling effect. Because the dark current is mainly dependent on the trap states as a result of modification of the lifetimes of the electrons in the trap states, the tunneling processes can be modulated effectively by tuning the trap energy level, the trap density, and the tunnel mass.

Photodiodes serve as pivotal components in optical data links, where minimized dark current and junction capacitance is vital for improving the detection sensitivity and response speed of the devices. This study experimentally and theoretically demonstrates that the one-side junction photodiode (OSJ-PD) exhibits reduced dark current and diminished junction capacitance. Notably, the device has a capacitance density of $2.2 \times 10^{-4}\ \mathrm {pF} / \mu \mathrm {m}^{2}$ and a dark current density of $2.4 \times 10^{-5}\ \mathrm {nA} / \mu \mathrm {m}^{2}$ at −5 V bias. Numerical simulations of current-voltage characteristics reveal that Shockley-Read-Hall (SRH) and trap-assisted tunneling (TAT) currents dominate dark current at low reverse bias from 0 V to −14 V, while band-to-band tunneling (BBT) current prevails at higher reverse bias from −14 V to −20 V. This study, for the first time, explains the trend of the variation in the dark current curve with bias voltage based on the generation mechanisms of dark current. Furthermore, we have theoretically demonstrated that the dark current of the OSJ-PD is insensitive to defect density at low voltages, and attributed the low junction capacitance to the wide depletion layer nature of the OSJ-PDs. These findings provide a comprehensive understanding of carrier transport and give a demonstration to analyze the current variation within diverse photodiodes.

The HgCdTe avalanche photodiode (APD) with built-in gain mechanism has great application prospects in the field of weak light signal detection. Any dark current will be converted into noise affecting the work efficiency of photodetectors. Therefore, the study of dark current mechanism is an important way to obtain high performance HgCdTe APD. In this paper, the photoelectric detection mechanism of planar junction electron injection HgCdTe APD is systematically studied, focusing on two aspects of structural optimization design and performance improvement. The dependence of device performance parameters on structure parameters is obtained by comparing the simulation results and experimental results. The lower the trap concentration, the smaller the dark current under small reverse bias voltage is, and the higher the operation voltage is. The dark current density of HgCdTe APD array is about 10-8 A/cm2 under small bias voltage. In addition to the material parameters, the dark current is mainly related to the internal electric field, which is affected by the width and doping concentration of the depletion region. The results show that device structure is the major determinant for the performance difference of HgCdTe APD. The structural optimization direction of high-performance HgCdTe APD is to further suppress the local electric field and reduce the dark current by adjusting the process.

Silicon Photomultipliers (SiPMs) are widely utilized in fields such as Light Detection and Ranging (LiDAR), quantum communication, and biomedical imaging. However, their inherent dark count rate (DCR) severely degrades device performance. In modern standard Complementary Metal-Oxide-Semiconductor (CMOS) processes, elevated doping concentrations cause traditional abrupt junctions to exhibit extremely high peak electric fields within the avalanche region. This leads to a sharp increase in band-to-band tunneling (BTBT) and trap-assisted tunneling (TAT), which constitute the primary sources of DCR under high reverse bias. Graded junctions can effectively separate the high electric field region from the high defect concentration region spatially. This separation suppresses the dark carriers generated by tunneling effects, thereby significantly reducing the DCR. This paper investigates the impact of graded junctions—fabricated via optimized ion implantation and thermal annealing processes—on the DCR of Geiger-mode avalanche photodiode (GAPD) microcells through theoretical analysis, Technology Computer-Aided Design (TCAD) simulations, and experimental measurements. Simulation results indicate that the graded junction exhibits a higher breakdown voltage (22V) compared to the abrupt junction (19V), demonstrating superior voltage tolerance. Furthermore, its doping profile is more gradual, which positions the junction away from the high-defect surface region. Experimental measurements show that the DCR of the graded junction is 1.49 Kcps, which is lower than the 2.43 Mcps of the abrupt junction. This further confirms that the graded junction, formed by optimizing processes such as ion implantation and annealing, effectively reduces the DCR of the SiPM, providing a viable approach to maintaining both high photon detection efficiency (PDE) and low DCR.

Dark current represents a fundamental limiting factor in photodiode performance, establishing the noise floor and constraining detectivity in low-light applications. This comprehensive literature review examines publications covering the physical mechanisms underlying dark current generation and diverse techniques employed for its reduction. Covered mechanisms include diffusion current, Shockley–Read–Hall (SRH) generation–recombination, trap-assisted tunneling, band-to-band tunneling, and surface leakage, each examined with respect to its physical origin and characteristic signatures. Reduction strategies are categorized into thermal management approaches, surface passivation techniques including atomic-layer-deposited aluminum oxide (ALD Al2O3), guard ring architectures (attached, floating, and combined configurations), gettering and defect engineering methods, doping profile optimization, bias voltage management, and advanced device architectures such as pinned photodiodes and black silicon structures. A classification table organizes all the reviewed literature by material system, reduction technique, and key findings. Special emphasis is placed on silicon, germanium, III–V compounds, and emerging material photodiodes relevant to near-infrared detection, CMOS imaging, single-photon avalanche diodes (SPADs), and Time-of-Flight (ToF) applications.

Mid-wavelength infrared HgCdTe electron-initiated avalanche photodiodes (e-APDs) have presented excellent performances on resolving and counting photons. Aiming at low flux, the readout integrated circuit noise can be significantly reduced by certain device gain, and very low excess noise of HgCdTe e-APDs gives the opportunity for noise equivalent photon (NEPh) to be 1. Therefore, the main issue for signal-to-noise ratio of HgCdTe APD is gain normalized dark current density (GNDCD) at high reverse bias. In this work, the electric field distribution is optimized by designing the mesa device structure to suppress the tunneling current at high operating voltage. Furthermore, etching technology combining dry etching and wet etching and passivation technology based on plasma enhanced atomic layer deposition were used to reduce surface leakage current. Finally, 20 μm pitch 128 × 128 array HgCdTe APDs for cutoff wavelength 4.32 μm at 80 K corresponding to compositions xCd = 0.326 were fabricated, the measured GNDCD of the test unit is about 1.5–10 × 10−9 A/cm2 at 0–13 V, and very low excess noise guaranteed the NEPh to be 2.0 at gain = 93 and 1.6 at gain = 193.

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Abstract We proposed an improved front-illuminated GaN/AlGaN separate absorption and multiplication (SAM) ultraviolet avalanche photodiode (APD) based on physical analysis and device simulations. By inserting an Al0.2Ga0.8N p-type layer into the p-i-p-i-n APD structure, a built-in electric field resulted from polarization effect will be introduced to facilitate the transport of electrons from absorption layer to multiplication region. The enhanced heterostructure APD presents significantly higher multiplication gain compared with the homogeneous one. Moreover, the doping concentration and thickness of the interlayer were optimized according to device performances, because the interlay has important effects on the electric field distribution and energy-band profile of the front-illuminated SAM APD.

To enhance the impact ionization coefficient of holes, we proposed an improved solar-blind AlGaN avalanche photodiode (APD) structure by using a low-Al-composition AlGaN multiplication layer and a filter based on periodic photonic crystal together with a composition graded interlayer between separate absorption and multiplication regions. The simulation results show that the improved APD presents a lower breakdown voltage and dark current, and a higher optical gain when compared to its conventional counterpart. Further, we found that the composition graded interlayer can modify profitably energy-band profile of heterostructure interfaces besides adjusting the electric field distribution, which is beneficial to the injection of holes from the absorption region to multiplication region. Therefore, we optimized the doping concentration and thickness of the interlayer, and analyzed the effects of these parameters on the APD performances.

InGaAs/InP single photon avalanche photodiode (SPAD) is important for quantum communication, and LIDAR applications in the near-infrared (NIR) wavelength range, between 0.9 µm and 1.7 µm. Compared with other optoelectronic devices, SPAD has two main advantages: high quantum efficiency and high detection efficiency. In this study, the design and simulating of a separate absorption, grading, charge, and multiplication (SAGCM) structure InGaAs/InP SPAD were conducted by using COMSOL Multiphysics. The electric-field distribution was studied under the given thickness and dopant concentration of each layer of the SPAD. It was found that the edge pre-breakdown of planar-type SPAD resulted from the intense electric field at the junction bend can be prevent from happening by using gaussian type dopant distribution profile. The punch-through voltage and the breakdown voltage were also focused. The results show that the punch-through voltage and the breakdown voltage was 55 V and 65V respectively. In addition, the electric field nonuniformity of the avalanche area increases greatly after the bias voltage exceeded the punch-through voltage.

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The avalanche photodiode (APD) is experiencing rapid technological advancements and expanding applications. Effective electric field engineering in APDs is critical for enhancing performance. Traditional methods for the modulation of the electric field using the charge layer often cause the carrier accumulation and non-uniform electric field distribution, limiting the performance of the APD. In this work, groove rings are introduced in the multiplication layer to efficiently modulate the electric field in the InGaAs/Si APD. This modulation is similar to that produced by the charge layer but is more effective than traditional methods. The electric field in the absorption layer can be decreased by groove rings to decrease the dark current and increase the 3-dB bandwidth. The electric field in the multiplication layer can be increased by the groove rings, leading to the better avalanche multiplication and the improvement of the gain. Additionally, the avalanche voltage is reduced by groove rings, refining the electric field distribution at the bonded interface. Importantly, groove rings enable more efficient carrier transport by avoiding carrier accumulation associated with the doping concentration of the charge layer. These findings provide theoretical guidance to achieve a higher gain-bandwidth product (GBP) of the InGaAs/Si APD.

Detector research is rapidly advancing to meet the growing demands for long-wavelength infrared (LWIR) detectors in applications such as deep space exploration, medical imaging, meteorological detection, and thermal imaging. In this study, we propose a high-performance Type-II superlattices (T2SLs) long-wavelength infrared (LWIR) avalanche photodiode (APD) with a separate absorption and multiplication (SAM) structure. Compared to conventional LWIR detectors, this device achieves over a 100-fold increase in responsivity at 77 K. This advancement is attributed to the design of a separate multiplication layer with the wide bandgap material AlxGa1-xSb in the InAs/GaSb T2SLs LWIR APD, which suppresses the electric field in the absorption layer while maintaining high gain. Using computer-aided design technology, we analyzed the internal electric field values and IV characteristics under key layer parameters. Simulation results indicate that under 12 μm monochromatic light irradiation at 77 K, the device can achieve a responsivity exceeding 200 A/W. These features are comparable to the most advanced band-structure-engineered high-gain LWIR photodetectors based on Type-II superlattices. This structural design concept provides a practical and feasible approach to achieving high-performance T2SLs LWIR infrared detectors.

A planar In0.53Ga0.47As avalanche photodiode (APD) with a triple-stage cascaded InAlAs/InAlGaAs multiplication structure is designed and fabricated. Double zinc-diffusion p-n junction is formed to suppress the perimeter premature breakdown. A low dark current of 4.8 nA at around breakdown voltage is obtained at room temperature for a $40~\mu $ m diameter device with a maximum gain-bandwidth product of 216 GHz. The E-field profile is modulated by doping of a thin In0.52Al0.48As subcharge layer within each multiplication stage. Moreover, electron and hole potential wells are also introduced by the In0.52Al0.24Ga0.24As layers within each stage. The measured hole-initiated maximum gain factor and excess noise factor are 77 and F=6.3 at 200 K, respectively, which well agree with the predicted results base on the dead-space multiplication theory. These results indicate the planar multi-stage multiplication regime is a viable route for fabrication of APDs towards low excess noise while maintaining of a low dark current.

Effective amplification of weak solar-blind ultraviolet signals remains a significant challenge. This work proposes a high-performance AlGaN solar-blind ultraviolet avalanche photodiode (APD) exploiting a heterostructure polarization field modulation strategy. The device achieves a maximum gain exceeding <inline-formula> <tex-math notation="LaTeX">$10^{\mathbf {{6}}}$ </tex-math></inline-formula> at room temperature, with a distinct peak responsivity at 263 nm. It exhibits an external quantum efficiency of 1627% at a reverse bias of 15 V and maintains a low dark current of 8 nA at breakdown onset, demonstrating superior linear-regime gain characteristics and low leakage performance. By incorporating a specific n-doped insertion layer to construct a separate absorption and multiplication structure, the intentionally engineered heterostructure peak polarization field within insertion/multiplication layers significantly accelerates photogenerated holes and mitigates dead space effect, thus enabling the ultrahigh gain and contributing to a lower avalanche breakdown voltage. Furthermore, the strategic utilization of AlN/Al<inline-formula> <tex-math notation="LaTeX">${}_{\mathbf {{0}.{5}}}$ </tex-math></inline-formula> Ga<inline-formula> <tex-math notation="LaTeX">${}_{\mathbf {{0}.{5}}}$ </tex-math></inline-formula> N quantum structures during epitaxial growth effectively suppresses dislocation propagation, providing a critical material foundation for high-quality active regions. The synergy between advanced material epitaxy techniques and innovative device field modulation not only enables this high-performance APD but also offers significant potential for guiding performance enhancement in next-generation semiconductor optoelectronic devices.