深紫外LED内部结构改变提升性能与结构反馈控制

… (c) Schematic diagrams of DUV LED epitaxial structure and step-graded EBL structure, as well as IQE of four structures at 100 A/cm 2 . Reproduced with permission from ref (143). …

… to address this optimization problem. The results demonstrate that, based on the optimized structure, the overlap of the carrier wave functions in the active region of the DUV LED is …

A novel method of utilizing an intelligent algorithm to guide the light extraction surface structure designing process for deep-ultraviolet light emitting diodes (DUV-LEDs) is proposed and investigated. Two kinds of surface structures based on the truncated pyramid array (TPA) and truncated cone array (TCA) are applied, which are expected to suppress the total internal reflection (TIR) effect and increase the light extraction efficiency (LEE). By addressing particle swarm optimization (PSO), the TPA and TCA microstructures constructed on the sapphire layer of the flip-chip DUV-LEDs are optimized. Compared to the conventional structure design method of parameter sweeping, this algorithm has much higher design efficiency and better optical properties. At the DUV wavelength of 280 nm, as a result, significant increases of 221% and 257% on the LEE are realized over the two forms of optimized surface structures. This approach provides another design path for DUV-LED light extraction structures.

In this work, we hybridize an air cavity reflector and a nanopatterned sapphire substrate (NPSS) for making an inclined-sidewall-shaped deep ultraviolet micro light-emitting diode (DUV micro-LED) array to enhance the light extraction efficiency (LEE). A cost-effective hybrid photolithography process involving positive and negative photoresist (PR) is explored to fabricate air-cavity reflectors. The experimental results demonstrate a 9.88% increase in the optical power for the DUV micro-LED array with a bottom air-cavity reflector when compared with the conventional DUV micro-LED array with only a sidewall metal reflector. The bottom air-cavity reflector significantly contributes to the reduction of the light absorption and provides more escape paths for light, which in turn increases the LEE. Our investigations also report that such a designed air-cavity reflector exhibits a more pronounced impact on small-size micro-LED arrays, because more photons can propagate into escape cones by experiencing fewer scattering events from the air-cavity structure. Furthermore, the NPSS can enlarge the escape cone and serve as scattering centers to eliminate the waveguiding effect, which further enables the improved LEE for the DUV micro-LED array with an air-cavity reflector.

Deep ultraviolet light-emitting diodes (DUV LEDs) typically suffer from strong parasitic absorption in the p-epitaxial layer and rear metal contact/mirror. This problem is exacerbated by a substantial portion of the multiple quantum well (MQW) emissions having a strong out-of-plane dipole component, contributing to emission in widely oblique directions outside the exit cone of the front semiconductor emitting surface. To address this, we propose an architecture that leverages such a heavily oblique angular emission profile by utilizing spaced-apart or scattered volume emitter micropixels that are embedded in a low-index dielectric buffer film with a patterned top surface. This approach achieves high light extraction efficiency at the expense of enlarging the effective emission area, however, it does not require a high-index (e.g., sapphire) substrate or a lens or a nanotextured epi for outcoupling purposes. Hybrid wave and ray optical simulations demonstrated a remarkable larger than three to sixfold increase in light extraction efficiency as compared to that of a conventional planar LED design with a sapphire substrate depending on the assumed epi layer absorption, pixel size, and ratio of light emission area to the MQW active area. An extraction efficiency three times greater than that of a recent nanotextured DUV LED design was also demonstrated. This architecture paves the way for DUV LEDs to have a plug efficiency comparable to that of mercury lamps while being significantly smaller.

… Nikoobakht et al. demonstrate single AlGaN fin LED pixels and discuss the impact of fin aspect ratio on the enhancement of EQE in their devices. They show that optimizing the shape …

This study introduces innovative structural enhancements in deep ultraviolet LEDs (DUV-LEDs) to optimize Performance. By implementing a 46.9° sloped mesa sidewall, we have designed what we believe to be two novel structures: an n-electrode hole structure that extends the active region and an interrupted mesa structure that significantly enlarges the sidewall area. We investigated the effects of these structures on DUV-LED performance independently and demonstrated that both single structure devices surpass the performance of conventional DUV-LEDs. Notably, the interrupted mesa structure yields a more substantial performance enhancement at higher injection currents, while the n-electrode hole structure excels at lower currents. Meanwhile, this paper also prepared two kinds of DUV-LEDs with parallel and staggered rows of mesa and n-electrode holes by combining the above two single structures on the same device. Compared with the single structure device, the performance of these combined structure devices is further improved, in which the performance of the DUV-LEDs with staggered rows of mesa and n-electrode holes is even better, the external quantum efficiency (EQE) and wall plug efficiency (WPE) of 9.19% and 7.13% at 250 mA operating current, which is an improvement of 9.6% and 4.4%, respectively, compared with that of the conventional DUV-LEDs. Furthermore, the enhancement in performance will be augmented with an increase in current, due to the efficient conversion of active area to sidewall area. At 500 mA, the optical power of the staggered-array device is increased by 10.6% compared to conventional DUV-LEDs; at 1000 mA, the optical power is increased by 17.7%.

The superlattice electron blocking layer (EBL) has been proposed to reduce the electron leakage of the deep ultraviolet light emitting diodes (DUV-LEDs). However, the hole transport is hindered by the barriers of EBL and the improvement of hole injection efficiency still suffers enormous challenges. The superlattice step doped (SLSD) EBL is proposed to improve the hole injection efficiency while enhancing the electron confinement capability. The SLSD EBL enhances the electron confinement capability by multi-reflection effects on the electron wave function. And a built-in electric field towards the active region is generated by superlattice step doping, which facilitates the transport of holes into the multiple quantum wells. The Advaced Physical Model of Semiconductor Devices (APSYS) software is used to simulate the DUV-LEDs with conventional EBL, superlattice EBL, superlattice doped EBL, and SLSD EBL. The results indicate that the SLSD EBL contributes to the increased electron concentration in the multiple quantum wells, the reduced electron leakage in the p-type region, the increased hole injection current, and the increased radiative recombination rate. When the current is 60 mA, the external quantum efficiency of DUV-LED with SLSD EBL is increased to 5.27% and the output power is increased to 13.81 mW. The SLSD EBL provides a valuable reference for solving the problems of serious electron leakage and insufficient hole injection of the DUV-LEDs.

… By altering the epitaxial structure and electrode layout, they were able to minimize the cutoff … waveguide designs and quantum well structures that optimize carrier confinement, reduce …

The light extraction efficiency (LEE) for deep ultraviolet light-emitting diodes (DUV LEDs) is significantly sacrificed by the absorption of the p-GaN layer. In this work, the self-aligned etching process is employed to laterally over-etched periphery thin p-GaN under the p-electrode by 10 µm to further improve the performance of AlGaN-based LEDs with various chip sizes. We find that when compared with reference devices with chip sizes of 40 × 40 µm2, 60 × 60 µm2 and 100 × 100 µm2, the optical power levels for the proposed DUV LEDs are enhanced by 16.66%, 11.41% and 7%, respectively. The most optical power enhancement can be obtained for the 40 × 40 µm2 DUV micro-LED chip. Hence, it is indicated that the laterally over-etched p-GaN design is more effective in increasing the LEE for DUV LEDs with reduced chip size. This shows the potential of the self-aligned etching p-GaN process in enhancing the LEE of DUV micro-LEDs. In addition, the lateral over-etched thin p-GaN suppresses the carrier diffusion to the device edge, which reduces the diffusion capacitance therein, hence leading to an increased −3 dB bandwidth to 55.4 MHz from 75.9 MHz for the packaged device of 100 × 100 µm2.

As demonstrated during the COVID-19 pandemic, advanced deep ultraviolet (DUV) light sources (200–280 nm), such as AlGaN-based light-emitting diodes (LEDs) show excellence in preventing virus transmission, which further reveals their wide applications from biological, environmental, industrial to medical. However, the relatively low external quantum efficiencies (mostly lower than 10%) strongly restrict their wider or even potential applications, which have been known related to the intrinsic properties of high Al-content AlGaN semiconductor materials and especially their quantum structures. Here, we review recent progress in the development of novel concepts and techniques in AlGaN-based LEDs and summarize the multiple physical fields as a toolkit for effectively controlling and tailoring the crucial properties of nitride quantum structures. In addition, we describe the key challenges for further increasing the efficiency of DUV LEDs and provide an outlook for future developments. This paper review recent advances in ultraviolet LEDs and summarize that multiple physical fields could built a toolkit for effectively controlling and tailoring crucial properties of nitride quantum structures.

In this study, deep ultraviolet (DUV) LEDs with 280 nm emission wavelength were successfully fabricated on 3-inch (1000) substrates using plasma-assisted molecular beam epitaxy (PAMBE) system. To further enhance the light extract efficiency of the DUV LEDs, the effects of the thickness of the p-type epitaxial layer and the material of the p-side metal reflector on the light output power of the flip-chip DUV LEDs were deeply investigated. Firstly, through an optical resonance model, we determined that the LED structures output light intensity is higher when the thickness of the p-type epitaxial layer is $\mathbf{0. 4 5 - 0. 5}$ times the emission wavelength. Experimental analysis confirmed that when the p-type epitaxial layer thickness is 0.49 times the emission wavelength, the light output power of the 280 nm DUV LED reaches approximately 6 mW. This experimental result is in complete agreement with the theoretical simulation. Secondly, furthermore, the study increased the direct contact area ratio of aluminum on the p-type GaN surface to $75 \%$ using a nickel/aluminum contact metal grid method. This grid metal contact method not only retains the good ohmic contact between nickel and p-type GaN but also enhances the reflectivity of DUV light at the p-type GaN and contact metal interface. Ultimately, this increased the light output power of the 280 nm DUV LED to approximately 8 mW.

… This structure enables enhanced Mg-activation, optimized band alignment, improved hole transport … of the proposed growth strategy for high-performance AlGaN-based DUV emitters. …

… The details of DUV fabrication are outlined in the context of achieving optimal DUV LED … Epitaxial structures were grown on c-plane sapphire substrates by a combination of …

… deep UV-LEDs by using SiLENSE module of the SimuLED software tool. We have optimized … We have observed that optimization of structural properties plays a crucial role in improving …

We propose a photonic crystal (PhC) design strategy for AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) using either air–hole or nanowire arrays to simultaneously enhance light extraction efficiency (LEE) and to enable vertical emission directionality. By selecting resonant modes at the Γ point and engineering their electric field distributions to avoid spatial overlap with the absorptive p-GaN contact layer, optical absorption is effectively suppressed. Both air–hole and nanowire photonic crystal structures generate vertical light emission through band-edge mode at the Γ point. The LEE of the air–hole configuration reached up to 56.5%, while that of the nanowire design reaches up to 76.1%, significantly outperforming conventional planar LEDs. Considering the reduced area of the active region in photonic crystals, the effective LEE is defined to evaluate the overall performance, evidencing the advantages of both the air–hole and the nanowire structures over the planar counterpart. By replacing the absorptive p-type GaN contact layer with a transparent p-type material, such as Al0.65Ga0.35N or h-BN, both photonic crystal designs exhibit much higher LEE boost compared to the planar counterpart. These results establish an effective approach to overcome the dual challenges of total internal reflection and light absorption in DUV LEDs.

Deep ultraviolet light-emitting diodes (DUV LEDs) operating at 254 nm face significant challenges in achieving efficient hole injection, resulting from the low p-type doping efficiency of high-Al-content AlGaN and the consumption of holes caused by severe electron leakage. To address these issues, a 45-nm-thick tunnel junction (TJ) contact layer (CL) is introduced to enhance hole generation. Furthermore, an asymmetric polarization-induced doping (PID) electron blocking layer (EBL) is proposed to suppress electron leakage. The performance of a conventional DUV LED, a DUV LED with 25-nm-thick TJ CL, a DUV LED with 45-nm-thick TJ CL, a DUV LED with 45-nm-thick TJ CL and V-shaped EBL, a DUV LED with 45-nm-thick TJ CL and symmetric PID EBL, and a DUV LED with 45-nm-thick TJ CL and asymmetric PID EBL is simulated using the advanced physical model of semiconductor devices (APSYS) software. The results indicate that incorporating a 45-nm-thick TJ CL enhances hole generation and reduces turn-on voltage. However, without an optimized EBL, severe electron leakage persists in the DUV LED with a 45-nm-thick TJ CL. The utilization of an asymmetric PID EBL increases the effective barrier height in the conduction band for electrons while reducing it in the valence band for holes. As a result, electron leakage is effectively suppressed, and hole injection is enhanced. Due to the increased carrier injection, the DUV LED with a 45-nm-thick TJ CL and an asymmetric PID EBL exhibits the highest radiative recombination and spontaneous emission rate. At an injection current of 75 mA, the internal quantum efficiency (IQE) reaches 25.1%, while the output power increases to 6.0 mW. In conclusion, the combination of a 45-nm-thick TJ CL and an asymmetric PID EBL offers a theoretically effective approach to mitigating the issue of insufficient hole injection in 254 nm DUV LEDs.

AlGaN-delta-GaN quantum well (QW) structures have been demonstrated to be good candidates for the realization of high-efficiency deep-ultraviolet (DUV) light-emitting diodes (LEDs). However, such heterostructures are still not fully understood. This study focuses on investigation of the optical properties and efficiency of the AlGaN-delta-GaN QW structures using self-consistent six-band k⸱p modelling and finite difference time domain (FDTD) simulations. Structures with different Al contents in the AlxGa1−xN sub-QW and AlyGa1−yN barrier regions are examined in detail. Results show that the emission wavelength (λ) can be engineered through manipulation of delta-GaN layer thickness, sub-QW Al content (x), and barrier Al content (y), while maintaining a large spontaneous emission rate corresponding to around 90% radiative recombination efficiency (ηRAD). In addition, due to the dominant transverse-electric (TE)-polarized emission from the AlGaN-delta-GaN QW structure, the light extraction efficiency (ηEXT) is greatly enhanced when compared to a conventional AlGaN QW. Combined with the large ηRAD, this leads to the significant enhancement of external quantum efficiency (ηEQE), indicating that AlGaN-delta-GaN structures could be a promising solution for high-efficiency DUV LEDs.

AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) suffer from severe quantum confined Stark effect (QCSE) due to the strong polarization field in the quantum wells (QWs) grown on c-plane substrates. In this paper, we propose a novel DUV LED structure embedded with graded QWs in which the Al composition was linearly changed to screen the QCSE. A significant increase of the internal quantum efficiency and thus an enhancement of the light output power by nearly 67% can be achieved, attributing to the improvement of the electron-hole wave function overlap (Гe-hh) to 58.6% in the Increased-Al-composition graded QWs, as compared to the QW without grading (Гe-hh = 40.4%) and reverse grading (Гe-hh = 33.6%). Further investigations show that the grading profile of the Al composition in the QWs, including either linearly increases or decreases along the growth direction and the thickness of graded QWs, determine the polarization electrical field in the QWs and as a result, significantly affecting the performance of the devices. In the end, a careful optimization of the graded QWs is called. The proposed structure with such unique graded QWs provides us an effective solution to suppress the QCSE effect in the pursuit of high-performance DUV emitters.

We explore the effect of the sub-well centers and related carrier dynamics mechanisms in dislocation-free DUV AlGaN/AlGaN multiple quantum wells (MQWs) homoepitaxially grown on AlN substrate. Cross...

… In this paper we will describe the approaches that we have used to grow AlGaN-based multiple quantum well deep UV LED structures and to overcome issues of doping efficiency, …

The characteristics of AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) with polarization-doped p-type layers were numerically analyzed. The energy band diagrams, carrier distributions in the multiple quantum wells (MQWs) and the p-type regions, electroluminescence spectra, current-versus-voltage (I-V) curves, and radiative recombination rates in MQWs, were investigated. The results indicate that DUV LEDs with polarization-doped p-type layers have lower electron leakage, better hole injection efficiency, and higher lighting emission intensity over conventional DUV LEDs. The results also reveal a significant improvement on these characteristics by increasing the Al content of the last quantum barrier in polarization-doped DUV LEDs.

… In this investigation, we fabricated AlGaN quantum well DUV-LEDs using MQB to … nm AlGaN quantum well DUV-LEDs using MQB is illustrated in Fig. 9. In the case of 250-nm DUV-LEDs…

Abstract Characteristics of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) with step-like and Al-composition graded quantum wells have been investigated. The simulation results show that compared to DUV-LEDs with the conventional AlGaN multiple quantum wells (MQWs) structure, the light output power (LOP) and efficiency droop of DUV-LEDs with the Al-composition graded wells were remarkably improved. The key factor accounting for the improved performance is ascribed to the better modulation of carrier distribution in the quantum wells to increase the overlap between electron and hole wavefunctions, which contributes to more efficient recombination of electrons and holes, and thereby a significant enhancement in the LOP.

… A deep ultraviolet (DUV) laser diode is a compact and efficient semiconductor device that … (EBL) and quantum barriers (QBs) to improve the performance of AlGaN-based Deep UV-LDs. …

In this study, high internal-quantum-efficiency (IQE) AlGaN multiple quantum wells (MQWs) were successfully demonstrated on low-defect-density AlN templates with nano-patterned sapphire substrates. These templates consisted of AlN structures with 0∼30 periods superlattices (SLs) by alternating high (100) and low (25) V/III ratios under a low growth temperature (1130 °C). Compared to conventional high crystal-quality AlN epilayers achieved at temperatures ≥1300 °C, lower thermal budget can reduce the production cost and wafer warpage. Via optimization of the SL period, the AlN crystallinity was systematically improved. Strong dependence of SL period number on the X-ray full-width-at-half-maximum (FWHM) of the AlN epilayer was observed. The AlN template with 20-period SLs exhibited the lowest FWHM values for (0002) and (10ī2), namely 331 and 652 arcsec, respectively, as well as an ultra-low etching pit density of 1 × 105 cm−2. The relative IQE of 280 nm AlGaN MQWs exhibited a dramatically increase from 22.8% to 85% when the inserted SL increased from 0 to 20 periods. It has hardly ever been reported for the AlGaN MQW sample. The results indicate that the engineered AlN templates have high potential applications in deep ultraviolet light emitters.

… of AlGaN based multi-quantum well near-ultra violet light emitting diodes (MQW-UV-LED) for … of AlN (to make AlGaN) takes it further towards deep UV region. That’s why most of the UV-…

AlGaN-based light-emitting diodes (LEDs) operating in the deep-ultraviolet (DUV) spectral range (210–280 nm) have demonstrated potential applications in physical sterilization. However, the poor external quantum efficiency (EQE) hinders further advances in the emission performance of AlGaN-based DUV LEDs. Here, we demonstrate the performance of 270-nm AlGaN-based DUV LEDs beyond the state-of-the-art by exploiting the innovative combination of bandgap engineering and device craft. By adopting tailored multiple quantum wells (MQWs), a reflective Al reflector, a low-optical-loss tunneling junction (TJ) and a dielectric SiO2 insertion structure (IS-SiO2), outstanding light output powers (LOPs) of 140.1 mW are achieved in our DUV LEDs at 850 mA. The EQEs of our DUV LEDs are 4.5 times greater than those of their conventional counterparts. This comprehensive approach overcomes the major difficulties commonly faced in the pursuit of high-performance AlGaN-based DUV LEDs, such as strong quantum-confined Stark effect (QCSE), severe optical absorption in the p-electrode/ohmic contact layer and poor transverse magnetic (TM)-polarized light extraction. Furthermore, the on-wafer electroluminescence characterization validated the scalability of our DUV LEDs to larger production scales. Our work is promising for the development of highly efficient AlGaN-based DUV LEDs.

… new DUV LEDs. … potential wells keep the electrons and holes in the MQWs active region and prevent them leaking into the p-side and n-side, respectively. The bandgap engineering of …

High‐quality epitaxy consisting of Al1−xGaxN/Al1−yGayN multiple quantum wells (MQWs) with sharp interfaces and emitting at ≈280 nm is successfully grown on sapphire with a misorientation angle as large as 4°. Wavy MQWs are observed due to step bunching formed at the step edges. A thicker QW width accompanied by a greater accumulation of gallium near the macrostep edge than that on the flat‐terrace is observed on 4° misoriented sapphire, leading to the generation of potential minima with respect to their neighboring QWs. Consequently, a significantly enhanced photoluminescence intensity (at least ten times higher), improved internal quantum efficiency (six times higher at low excitation laser power), and a much longer carrier lifetime are achieved. Importantly, the wafer‐level output‐power of the ultraviolet light emitting diodes on 4° misoriented substrate is nearly increased by 2–3 times. This gain is attributed to the introduction of compositional inhomogeneities in AlGaN alloys induced by gallium accumulation at the step‐bunched region thus forming a lateral potential well for carrier localization. The experimental results are further confirmed by a numerical modeling in which a 3D carrier confinement mechanism is proposed. Herein, the compositional modulation in active region arising from the substrate misorientation provides a promising approach in the pursuit of high‐efficient ultraviolet emitters.

AlGaN‐based deep‐ultraviolet (DUV) light‐emitting diodes (LEDs) hold great promise for a wide range of applications, including water sterilization, biochemical sensing, and UV curing. However, their efficiency is fundamentally limited by the quantum‐confined Stark effect (QCSE) originating from strong spontaneous and piezoelectric polarization fields in c‐plane quantum wells (QWs). These internal fields induce pronounced band bending and spatial separation of electron and hole wavefunctions. In this work, a multiple quantum well (MQW) design with a linearly graded‐aluminum composition is introduced along the [0001] direction of the QWs. The grading suppresses polarization discontinuities at quantum barrier (QB)/quantum well (QW) interfaces, reducing interface‐bound charges, and simultaneously generates distributed bulk polarization charges that create a reverse internal electric field. This counter‐field mitigates QCSE, resulting in flattened band profiles and improved wavefunction overlap. Technology computer‐aided design (TCAD) simulations using the SILVACO Advanced Technology Large‐Area Simulator (ATLAS) platform show an increase in electron–hole overlap from 92.45% to 98.26%, a 44.16% enhancement in light output power, a 63.6% reduction in internal electric field, and a 0.7 V decrease in forward voltage. The novelty of this work lies in applying in‐well linear compositional grading as a polarization‐field engineering technique for AlGaN QWs, enabling simultaneous enhancement of optical and electrical performance.In this work, a practical, scalable, and simulation‐verified pathway toward high‐efficiency AlGaN‐based DUV LEDs is reported.

AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) still confront many challenges, which is partially limited by the poor carrier injection in the active region. Although incorporating a high Al-composition quantum barrier (QB) may boost carrier confinement capability, it will aggravate the quantum confined Stark effect (QCSE) and thus deteriorate the optical performance. In this article, a DUV LED structure with step-like QBs has been proposed and carefully investigated. This unique QB structure suppresses the electron overflow into the p-side of the device and benefits the hole injection efficiency simultaneously, thereby promoting the radiative recombination rate in the active region. As a result, the internal quantum efficiency (IQE) and light output power (LOP) of the DUV LED with step-like QBs are significantly improved with an enhancement factor of 40% under 60 mA current injection. Therefore, our step-like QB design provides a feasible approach to the enhancement of the optical performance of DUV LEDs.

Vertically injected thin-film ultraviolet light-emitting diodes operating at 325 and 280nm are demonstrated. Low-temperature AlN interlayers allow crack-free growth of AlxGa1−xN with compositions up to x=0.53 on GaN-on-sapphire templates. The GaN layer allows laser-induced separation of the highly strained epi stack from the sapphire substrate with high yield. Cathode contacts are formed on nitrogen-face AlxGa1−xN (up to x=0.53) and allow vertical injection of current into the active region. Controlled roughening of the nitrogen-face AlxGa1−xN is also demonstrated through photoelectrochemical etching and results in >2.5× light extraction gain for 325 and 280nm devices.

AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) still suffer from relatively low light output power (LOP) and poor external quantum efficiency (EQE) due to the severe electron leakage and hole-blocking effects. Electrons tend to accumulate in the last quantum well (LQW) and escape from the active region because of the weak confinement ability of the quantum barriers (QBs). Besides, the polarization-induced positive charges at the last QB (LQB)/p-type electron blocking layer (p-EBL) interface will attract electrons and consume holes for nonradiative recombination, leading to inadequate carrier concentration in the active region. In this article, we propose DUV LEDs with V-shaped multiple quantum wells (MQWs) to modulate the distribution of carriers in the active region. With the V-shaped MQWs, carriers are inclined to accumulate in the middle quantum well (QW) instead of the last one, and the polarization-induced electric field in the middle QW is also well alleviated, contributing to improved radiative recombination rates. Furthermore, the original positive sheet charges at the LQB/p-EBL interface are converted into negative ones, which is beneficial for suppressing electron overflow and increasing hole injection efficiency. Therefore, the EQE is remarkably improved by 48.1% at an injection current of 150 A/cm2. The V-shaped MQWs provide an effective solution to realize DUV LEDs with high performance.

Optical and electrical performance and the relevant physical properties of deep ultraviolet (DUV) AlGaN-based light-emitting diodes (LEDs) are numerically investigated. The influence of bulk AlGaN electron-blocking layer (EBL) with various Al compositions and Mg-doping concentrations on the output performance of DUV LEDs is systemically explored. Simulation results show that the DUV LED with bulk Al_0.85Ga_0.15N EBL with a relatively low Mg-doping concentration of <inline-formula> <tex-math notation="LaTeX">$2\times 10^{19}$ </tex-math></inline-formula> cm⁻³ may have high wall-plug efficiency. The LED structure with Al_0.55Ga_0.45N/Al_0.75Ga_0.25N superlattice (SL) EBL is proposed in this study, which is shown to have high wall-plug efficiency similar to the LED with bulk Al_0.85Ga_0.15N EBL while the Al composition of AlGaN EBL can be effectively reduced. The proposed LED structure with SL EBL provides a practical way to fabricate high-crystalline-quality and high-efficiency DUV LEDs.

AlGaN-based deep UV (DUV) LEDs generally employ a p-type electron blocking layer (EBL) to suppress electron overflow. However, Al-rich III-nitride EBL can result in challenging p-doping and large valence band barrier for hole injection as well as epitaxial complexity. As a result, wall plug efficiency (WPE) can be compromised. Our systematic studies of band diagram and carrier concentration reveal that carrier concentrations in the quantum well and electron overflow can be significantly impacted because of the slope variation of the quantum barrier (QB) conduction and valence bands, which in turn influence radiative recombination and optical output power. Remarkably, grading the Al composition from 0.60 to 0.70 for the 12-nm-thick AlGaN QB of the DUV LED without the EBL can lead to 13.5% higher output power and similar level of overflown electron concentration (∼1 × 1015/cm3) as opposed to the conventional DUV LED with the p-type EBL. This paradigm is significant for the pursuit of higher WPE or shorter emission wavelength for DUV LEDs and lasers, as it provides a new direction for addressing electron overflow and hole injection issues.

Electron-leakage is a deep-rooted problem for nitride-based light-emitting diodes (LEDs), particularly for AlGaN-based deep-ultraviolet (DUV) LEDs. In this paper, a specific design for the electron-blocking structure in AlGaN DUV LEDs, increasing the Al composition of the last quantum barrier to the same value as that of the electron-blocking layer accompanied with composition-graded p-AlGaN layer, is proposed to reduce electron leakage. Simulation results demonstrate that this design can effectively reduce electron leakage and hence increase internal quantum efficiency. Furthermore, fabricated devices with at an emitting wavelength of 292 nm verify remarkably enhanced light-output power. At 20-mA injection current, the proposed structure achieved a light-output increment as high as 98%, compared with the conventional structure.

… electron-blocking layers (EBL) on the output performance of deep-ultraviolet (DUV) light-emitting diodes (LEDs) … Under this design, the QW layers create tensile strain and the QB layers …

To prevent electron leakage in deep ultraviolet (UV) AlGaN light-emitting diodes (LEDs), Al-rich p-type AlxGa(1−x)N electron blocking layer (EBL) has been utilized. However, the conventional EBL can mitigate the electron overflow only up to some extent and adversely, holes are depleted in the EBL due to the formation of positive sheet polarization charges at the heterointerface of the last quantum barrier (QB)/EBL. Subsequently, the hole injection efficiency of the LED is severely limited. In this regard, we propose an EBL-free AlGaN deep UV LED structure using graded staircase quantum barriers (GSQBs) instead of conventional QBs without affecting the hole injection efficiency. The reported structure exhibits significantly reduced thermal velocity and mean free path of electrons in the active region, thus greatly confines the electrons over there and tremendously decreases the electron leakage into the p-region. Moreover, such specially designed QBs reduce the quantum-confined Stark effect in the active region, thereby improves the electron and hole wavefunctions overlap. As a result, both the internal quantum efficiency and output power of the GSQB structure are ~2.13 times higher than the conventional structure at 60 mA. Importantly, our proposed structure exhibits only ~20.68% efficiency droop during 0–60 mA injection current, which is significantly lower compared to the regular structure.

… electron blocking layer (EBL) and AlGaN/GaN superlattice (SL) EBL with various thicknesses of AlGaN layers on NUV LEDs … by some specific designs for the electron blocking layer,” Opt…

The characteristics of the ultraviolet light-emitting diode (LED) with conventional and specifically designed electron blocking layers (EBLs) are investigated numerically and experimentally in this work. Simulation results show that delicately designed EBLs can not only capably perform the electron blocking function but also eliminate the incidental drawback of obstruction of hole injection caused by the nature of the large polarization field at the c-plane nitride heterojunction. It is shown that the polarization induced downward band bending can be mitigated when the portion of conventional EBL lying adjacent to the active region is replaced by a graduated AlGaN layer. The conduction band profile indicates that this replacement structure could have the capability of electron confinement similar to the conventional structure, and the valence band profile indicates that the spike induced by the polarization field is simultaneously eliminated, assisting the process of hole injection and distribution in the active region. Electron leakage over the EBL is thus obviously reduced, and the consumption efficiency of the injection carriers is improved, as expressed in the distribution of the electron current density. The experimental results show that the light output power can be significantly enhanced from 29.3 mW for the conventional device to 54.7 mW for the LED with the redesigned EBL structure.

… We propose a design for highly efficient AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) using a heart-shaped graded Al composition electron-blocking layer (EBL). This …

… ultraviolet light-emitting diodes (UV-LEDs).1-3 Recently, deep-ultraviolet LEDs (DUV-LEDs), … We designed the DUV-LED structures shown in Figure 1 to study the impact of the GEBL …

… -varying AlGaN electron blocking layer (EBL) is introduced in the N-face AlGaN UV-LEDs. Detailed … the designs for different wavelengths in the UV range, we design the other two N-face …

… electronblocking layer (EBL) on the characteristics of the ultraviolet light-emitting diodes (UV-LEDs) … Sheng, “On the importance of AlGaN electron blocking layer design for GaN-based …

… LED is currently inferior to that of the visible-light LED. Recently, commercialized UVC LEDs have achieved external quantum efficiency (EQE) of 6.4%, whereas the visible-light LED …

… about the electron-blocking mechanism in the UVB LED. … Aluminum gallium nitride (AlGaN) based UVB LEDs are delivering an … Such issues in UVB LEDs are attributed to using …

… ultraviolet light-emitting diodes (DUV LEDs) with quaternary last quantum barrier (QLQB) and step-graded electron blocking layer (… to the optimal recombination of electron–hole pairs in …

… ultraviolet absorption in the p-GaN contact layer. Drawing inspiration from the electron-blocking layer … a hole-transport layer in n-ZnO/p-hBN/p-GaN/sapphire ultraviolet LEDs has been …

In this study, impacts of quantum barrier (QB) width on the device performance of deep-ultraviolet (DUV) light-emitting diode (LED) are investigated theoretically under different crystal quality. Simulation results show that, in comparison with the first QB and middle QBs, the last QB (LQB) plays a much more important role in DUV LEDs. Specifically, the capability of electron confinement and relevant electron current leakage are critically affected by the thickness of LQB, especially at a high degree of polarization or with high crystalline quality. Furthermore, if a DUV LED is with a thin LQB, e.g., 3-nm-thick LQB, the light output power and wall-plug efficiency (WPE) can be maintained relatively high under the situation of either low or high degree of polarization. Thin LQB is thus favorable for the DUV LEDs with high crystalline quality due to the good confinement capability under a high degree of polarization.

In this study, we investigate a unique Al-content engineered superlattice electron blocking layer (AESL-EBL) for improving the charge carrier transport properties of AlGaN quantum well (QW) deep ultraviolet (DUV) light-emitting diode (LED) structures. LED structures without EBL, with conventional bulk EBL (BEBL), and superlattice EBL (SL-EBL) are used for comparison. It is found that the LED structure with the AESL-EBL can exhibit superior electron blocking and hole injection, leading to reduced efficiency droop and improved light output power, compared to LED structures without EBL and with BEBL. Notably, the LED structure with AESL-EBL also outperforms the LED structure with SL-EBL, benefitting from the Al-content engineered SL. In the end, such an ASEL-EBL is applied to a DUV laser diode structure, and by optimizing the device structure low Mg-induced internal loss of around 1 cm−1 can be obtained.

Deep‐ultraviolet (DUV) solar‐blind communication (SBC) shows distinct advantages of non‐line‐of‐sight propagation and background noise negligibility over conventional visible‐light communication. AlGaN‐based DUV micro‐light‐emitting diodes (µ‐LEDs) are an excellent candidate for a DUV‐SBC light source due to their small size, low power consumption, and high modulation bandwidth. A long‐haul DUV‐SBC system requires the light source exhibiting high output power, high modulation bandwidth, and high rate, simultaneously. Such a device is rarely reported. A parallel‐arrayed planar (PAP) approach is here proposed to satisfy those requirements. By reducing the dimensions of the active emission mesa to micrometer scale, DUV µ‐LEDs with ultrahigh power density are created due to their homogeneous injection current and enhanced planar isotropic light emission. Interconnected PAP µ‐LEDs with a diameter of 25 µm are produced. This device has an output power of 83.5 mW with a density of 405 W cm−2 at 230 mA, a wall‐plug efficiency (WPE) of 4.7% at 155 mA, and a high −3 dB modulation bandwidth of 380 MHz. The remarkable high output power and efficiency make those devices a reliable platform to develop high‐modulation‐bandwidth wireless communication and to meet the requirements for bio‐elimination.

Aluminum gallium nitride (AlGaN)-based deep ultraviolet (DUV) light-emitting diodes (LEDs) hold tremendous potential and application prospects. However, DUV LEDs face challenges such as low internal quantum efficiency (IQE) and degraded...

In this work, we demonstrate a straightforward and effective strategy, so called perimeter-to-area ratio (P/A ratio) engineering, to enhance the optical performance of deep-ultraviolet micro-scale LED (DUV <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>-LEDs). Specifically, we designed and fabricated three types of DUV <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>-LEDs architectures with circle, pentagon, and quadrangle shapes which possess different P/A ratios, and found that the external quantum efficiency (EQE) of the quadrilateral <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>-LEDs exhibit the highest value thanks to its largest P/A ratio in the LED mesa covered by the p-electrode, leading to a higher light output power than that of <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>-LED in circle shape by 29.2% at an injection current density of 3000 A/cm<inline-formula> <tex-math notation="LaTeX">$^{\mathbf {{2}}}$ </tex-math></inline-formula>. More importantly, such superior performance due to the increased P/A ratio of <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>-LEDs is becoming more remarkable when the size of <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>-LEDs further shrinks, attributing to a larger light extraction, more uniform current spreading, and better sidewall out-radiation of self-generated heat of the <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>-LEDs.

The current pandemic crisis caused by SARS-CoV-2 has also pushed researchers to work on LEDs, especially in the range of 220–240 nm, for the purpose of disinfecting the environment, but the efficiency of such deep UV-LEDs is highly demanding for mass adoption. Over the last two decades, several research groups have worked out that the optical power of GaN-based LEDs significantly decreases during operation, and with the passage of time, many mechanisms responsible for the degradation of such devices start playing their roles. Only a few attempts, to explore the reliability of these LEDs, have been presented so far which provide very little information on the output power degradation of these LEDs with the passage of time. Therefore, the aim of this review is to summarize the degradation factors of AlGaN-based near UV-LEDs emitting in the range of 200–350 nm by means of combined optical and electrical characterization so that work groups may have an idea of the issues raised to date and to achieve a wavelength range needed for disinfecting the environment from SARS-CoV-2. The performance of devices submitted to different stress conditions has been reviewed for the reliability of AlGaN-based UV-LEDs based on the work of different research groups so far, according to our knowledge. In particular, we review: (1) fabrication strategies to improve the efficiency of UV-LEDs; (2) the intensity of variation under constant current stress for different durations; (3) creation of the defects that cause the degradation of LED performance; (4) effect of degradation on C-V characteristics of such LEDs; (5) I-V behavior variation under stress; (6) different structural schemes to enhance the reliability of LEDs; (7) reliability of LEDs ranging from 220–240 nm; and (8) degradation measurement strategies. Finally, concluding remarks for future research to enhance the reliability of near UV-LEDs is presented. This draft presents a comprehensive review for industry and academic research on the physical properties of an AlGaN near UV-LEDs that are affected by aging to help LED manufacturers and end users to construct and utilize such LEDs effectively and provide the community a better life standard.

Efficiency of AlGaN deep-UV LEDs is considerably lower than that of InGaN/GaN based blue and green light emitters because of (i) a lower internal quantum efficiency controlled by threading dislocation density, (ii) strong absorption of UV light by metallic contacts and conventionally used p-GaN contact layer, and (iii) a lower electrical efficiency and enhanced LED self-heating originated from poor conductivity of AlGaN cladding layers and high AlGaN/metal Ohmic contact resistance. Coupled electrical, thermal and optical simulations allow identifying the critical factors limiting the deep-UV LED efficiency and suggesting ways to improve the device performance. In this work, we consider various approaches to optimization of deep-UV LEDs.

… structure of double-layer nano-pattern arrays (NPAs) for AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs… LEE), a major device performance bottleneck. The double-layer …

… the limit of internal lattice strain to the device structures. … strain can change the performance characteristics and provide … performance is particularly significant in DUV-LED structures …

Deep-ultraviolet light-emitting diodes (DUV LEDs) are encountering low external quantum efficiency (EQE) and light output power (LOP) due to the strong optical absorption to DUV light and the poor carrier injection efficiency. To solve these issues, we design and optimize a 250 nm DUV LED structure with thin quantum wells and discrete p-type functional layers. The discrete p-type functional layers consist of a high Al composition-gradient layer (layer I) and a low Al composition-gradient layer (layer II). Calculated results indicate that the use of thin quantum wells can rearrange the valence subband distributions to increase the transverse-electric (TE) polarized emission, thereby enhancing light extraction efficiency (LEE). Additionally, the LEE can also be increased by optimizing the thickness of the discrete p-type functional layers, i.e., modulating the optical absorption effect and the optical cavity effect. Meanwhile, we also investigate the impact of different negative polarization bulk charge densities on the electron and hole injections by changing the thickness of layer I and layer II, which can obtain the optimized internal quantum efficiency (IQE) for the 250 nm DUV LED. Therefore, when compared with conventional DUV LEDs, the proposed LED architectures improve the EQE and optical power if the discrete p-type functional layers are properly designed.

… In this work, the DUV LEDs under various degrees … DUV LEDs. Besides, since high film quality and high degree of polarization are closely correlated, it is necessary to design DUV LED …

Aluminium Gallium Nitride (AlGaN) based light emitting diodes (LED) are the enabling technology for compact emitters of deep ultraviolet (DUV) radiation and are in high demand for environmental and medical applications. The efficiency of recent DUV LEDs is in the range of a few percent providing some potential for improvement. Apart from the light extraction efficiency the hole injection into the active region presents a major obstacle towards more efficient DUV LEDs. In this work, we investigate the emission spectra of a mixed multi quantum well (MQW) DUV LED to attain details on the active region carrier transport that allow an improvement of the hole injection. Changing the position of the long wavelength marker quantum well yields characteristic emission spectra which have been modelled with a multi scale carrier transport and luminescence simulator. The numerical modelling enables the extraction of opaque carrier transport characteristics in AlGaN such as the hole mobility in the highly doped barriers of the MQW.

In this letter, we propose to enhance the hole injection efficiency by modulating the layer resistivity in the n-AlGaN layer for 280 nm AlGaN based deep ultraviolet light-emitting diodes (DUV LEDs). The layer resistivity for the n-AlGaN layer is controlled by generating the energy barriers, which is enabled by locally engineering the energy band gap for the n-AlGaN layer, such that a thin n-AlGaN layer with high Al composition is inserted before growing the subsequent multiple quantum wells (MQWs). As a result, such inserted n-AlGaN layer is able to tune the current flow path, i.e., improving the current spreading effect in the p-type hole injection layer. The improved current spreading effect favors the promoted hole injection into the active region. We numerically and experimentally obtain the improved external quantum efficiency, the optical power, and the wall-plug efficiency, thanks to the better current spreading and the correspondingly enhanced hole injection capability.

In this article, a novel graded superlattice (SL) p-AlGaN structure for deep ultraviolet light-emitting diode (DUV LED) capable of emitting 273 nm has been studied. It is observed that the output power in the case of graded SL p-AlGaN LED structure (GSLED) is significantly high (7.68-fold higher, at the current density of 200 A/cm2) compared with a conventional structure. Moreover, noticeable improvements in the maximum value of external quantum efficiency, as well as the efficiency droop, are achieved with the modified structures. The abrupt potential barrier height in conventional DUV LED (CLED) obstructs the hole injection inside the quantum well region. On the contrary, smoother band variation in GSLED prevents potential barrier height of hole and causes ease in the flow of hole into the quantum well (QW) region. Also, the electron concentration in the multiple-quantum-well (MQW) region for GSLED is increased by around 100% due to the reduced leakage of electrons toward the p-region.

… (QWs) of those DUV LEDs can considerably impact their … performance, since the carrier transport within the emitters is … band engineering technologies to achieve better DUV LEDs, …

… power for DUV LEDs, we designed and grew the DUV LED structures … The hole injection layer for both DUV LED devices is … Low parasitic carrier reservoir of AlGaN-based DUV-LED via …

Gallium nitride (GaN) and its related alloys, particularly aluminum gallium nitride (AlGaN), have emerged as promising materials for deep ultraviolet light-emitting diodes (DUV LEDs) due to their wide bandgap properties and solid-state emission advantages. These devices show broad application potential in areas such as water purification, biological sterilization, and medical diagnostics. However, DUV LEDs currently face significant challenges in terms of external quantum efficiency (EQE), thermal management, and device reliability. This review systematically summarizes the key limitations that hinder the performance of AlGaN-based DUV LEDs, including difficulties in achieving efficient p-type doping in high-Al-content materials, poor carrier injection efficiency, high thermal resistance, and high defect densities. In response to these bottlenecks, various state-of-the-art strategies aimed at improving both internal and external quantum efficiency are discussed, such as quantum well structure optimization, polarization-engineered tunnel junctions, crystalline quality enhancement, interface band engineering, and advanced light extraction designs. Furthermore, the review highlights critical approaches for reducing thermal resistance and enhancing device reliability, including the use of high thermal conductivity substrates, advanced packaging technologies, and thermal interface materials. Overall, the advancement of AlGaN-based DUV LEDs relies on coordinated innovations in materials, device architecture, and system-level integration to realize high-efficiency, high-reliability performance.

In deep-ultraviolet (DUV) light-emitting diodes (LEDs), it is difficult to obtain both efficient carrier confinement and high light extraction, which are quite sensitive to optical polarization and other physical parameters. In this paper, characteristics of DUV LEDs with various n-AlGaN layers and quantum barriers (QBs), and various widths of quantum wells (QWs) are investigated. Specifically, the capability of carrier confinement and properties of optical polarization are analyzed in detail. The simulation results show that LED structure with Al0.64Ga0.36N QBs, n-Al0.7Ga0.3N layer, and 4-nm-thick QWs, which has a peak emission wavelength of 284.5 nm at 60 mA, exhibits high internal quantum efficiency of 25% and high degree of optical polarization of 0.874.

… In this paper, optical and electrical characteristics of DUV LEDs … through band engineering to promote the capability of carrier … In this paper, characteristics of DUV LEDs with various QBs …

… which include the use of band engineering by utilizing compositionally graded AlGaN layers, … Such structure provides a promising path for higher carrier transport, lower resistance, and …

This paper reports the illustration of electron blocking layer (EBL)-free AlGaN light-emitting diodes (LEDs) operating in the deep-ultraviolet (DUV) wavelength at ∼270nm. In this work, we demonstrated that the integration of an optimized thin undoped AlGaN strip layer in the middle of the last quantum barrier (LQB) could generate enough conduction band barrier height for the effectively reduced electron overflow into the p-GaN region. Moreover, the hole injection into the multi-quantum-well active region is significantly increased due to a large hole accumulation at the interface of the AlGaN strip and the LQB. As a result, the internal quantum efficiency and output power of the proposed LED structure has been enhanced tremendously compared to that of the conventional p-type EBL-based LED structure.

For [0001]-oriented AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs), the severe electron leakage and poor hole injection efficiency significantly decline the external quantum efficiency (EQE) and optical power. In this work, we propose an insertion structure of AlxGa1−xN/AlyGa1−yN superlattice (SL) positioned between the p-type electron blocking layer (p-EBL) and the hole supplier layer (HSL), featuring a gradually decreasing Al composition within each well and barrier. Reduced potential barrier height for holes at the p-EBL/HSL interface can be achieved by the integration of the proposed SL structure, thereby augmenting the hole concentration in the active region. Besides, the net negative polarization charges generated across the embedded SL structure can facilitate the acceptor ionization and enhance hole injection efficiency. On the other hand, the inserted SL layer can effectively elevate the potential barrier height of electrons at the p-type region, consequently suppressing electron leakage. Therefore, compared to the reference DUV LEDs, the proposed DUV LEDs with the Al-composition-engineered SL insertion structure exhibit a 39.3% improvement in the EQE along with an 83.7% reduction in efficiency droop at 100 A/cm2. This design strategy offers an effective approach to improving the optoelectronic performance of DUV LEDs.

In this paper, a structure of super-lattice structure last barrier (SLSLB) is proposed, which can be applied into the AlGaN-based ultraviolet light-emitting diodes (LEDs) for improving the injection of both electrons and holes. Several other SLSLBs are also designed and compared in this work, and according to the simulated results, we find that the LED with SLSLB of diminishing thickness (SLSLB-D) possesses the highest internal quantum efficiency and the smallest efficiency droop. The SLSLB-D can effectively reduce the electron concentration at the interface between the last barrier (LB) and electron block layer (EBL), which relieves the leakage of electrons. Moreover, the best hole injection capability for the LED with SLSLB-D also contributes to the improved optical performance.

Deep ultraviolet (DUV) light-emitting diodes (LEDs) have attracted widespread attention in communication because of their lack of background noise interference in day-blind communications, but their low luminous efficiency and low response frequency cannot meet the requirements of non-visual optical communication systems. AlGaN-based micro-LEDs (<inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>-LEDs) can provide high light output power (LOP) due to their smaller chip size, and they can also withstand high current density due to their enhanced current diffusion uniformity. Thus, matrix-type DUV <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>-LEDs are effective candidates to enhance LOP and response frequency. In this work, a matrix-type AlGaN-based DUV communication LED with step-graded Al composition superlattice (SL) electron-blocking layer (EBL) at wavelength of 274 nm was designed, LOP and response frequency reached 45.4 mW and 414 MHz at 212 A/cm2 current density. After this SL EBL applied in the UV communication LED, hole injection capability was enhanced, high LOP and high response frequency make it be an ideal candidate for wireless communication applications.

Abstract In this paper, a new n-type confinement layer that uses the stepped and super-lattice structure to replace conventional n-type AlGaN layer of deep ultraviolet light-emitting diode (DUV LED) is investigated. The simulation results indicate that the new structure significantly enhances the light output power (LOP) and internal quantum efficiency (IQE) of DUV LED. This is because the capability of carrier confinement in the quantum wells (QWs) is enhanced; the carrier concentrations and the radiative recombination rate in the active region of DUV LED are improved.

The p-AlGaN/AlGaN superlattice (SL) hole injection structure was introduced into deep ultraviolet (DUV) light-emitting diodes (LEDs) to enhance their performances. The period thicknesses of the p-Al0.8Ga0.2N/Al0.48Ga0.52N SLs affected the performances of the DUV LEDs. The appropriate period thickness of the p-Al0.8Ga0.2N/Al0.48Ga0.52N SL may enhance the hole injection of DUV LEDs. Therefore, compared with the reference LEDs, the DUV LEDs with the 10-pair Al0.8Ga0.2N (1 nm)/Al0.48Ga0.52N (1 nm) SL presented forward voltage reduction of 0.23 V and light output power improvement of 15% at a current of 350 mA. Furthermore, the 10-pair Al0.8Ga0.2N (1 nm)/Al0.48Ga0.52N (1 nm) SL could slightly suppress the Auger recombination and current overflow of the DUV LEDs in a high-current operation region. In addition to improved carrier injection, the DUV LEDs with the p-Al0.8Ga0.2N/Al0.48Ga0.52N SL hole injection structure showed reduced light absorption at their emission wavelength compared with the reference LEDs. Therefore, the DUV LEDs with p-Al0.8Ga0.2N/Al0.48Ga0.52N SL may exhibit better light extraction efficiency than the reference LEDs. The enhancement of p-Al0.8Ga0.2N (1 nm)/Al0.48Ga0.52N (1 nm) SL may contribute to improvements in light extraction and hole injection.

Abstract A deep ultraviolet light-emitting diode (DUV LED) consisting of a specifically designed intermediate p-type region involving a superlattice quaternary nitride alloy has been proposed. The light output power of the proposed structure has been found significantly large; around 28.30 times high in comparison to the conventional structure, at the current density of 200 A/cm2. The maximum internal quantum efficiency of the proposed structure is 153.63% higher compared to the conventional one. Moreover, the efficiency droop has been reduced by 99.08%. Absence of abrupt potential barrier owing to the strain compensation provided by the superlattice p-AlInGaN layer offers an attractive solution for enhancing the hole injection into the active region leading to the improvement in performance of DUV LED.

Due to environmental friendliness, small size, long lifetime, and adjustable light-emitting wavelength, AlGaN-based deep ultraviolet light-emitting diodes (DUV-LEDs) have great development potential in the fields of biochemical detection, sterilization and disinfection, and non-line-of-sight communication. After decades of research, AlGaN-based DUV-LEDs have significantly improved in the direction of luminous efficiency. However, the luminous efficiency of the present AlGaN-based DUV-LEDs is still at a low level compared with that of the fully commercialised nitride blue LEDs, making it difficult to meet the market demand. This paper first introduces the present development status of AlGaN-based DUV-LEDs and the reasons for the low luminous efficiency. Then from the preparation of AlGaN-based, AlGaN doping and the design of AlGaN-based DUV-LEDs structure to elaborate the research progress in recent years in the direction of improving the luminous efficiency of AlGaN-based DUV-LEDs. Finally discusses the challenges that the AlGaN-based DUV-LEDs are presently faced with, and their future opportunities for development.

AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) suffer from electron overflow and insufficient hole injection. In this paper, novel DUV LED structures with superlattice electron deceleration layer (SEDL) is proposed to decelerate the electrons injected to the active region and improve radiative recombination. The effects of several chirped SEDLs on the performance of DUV LEDs have been studied experimentally and numerically. The DUV LEDs have been grown by metal-organic chemical vapor deposition (MOCVD) and fabricated into 762 × 762 μm2 chips, exhibiting single peak emission at 275 nm. The external quantum efficiency of 3.43% and operating voltage of 6.4 V are measured at a forward current of 40 mA, indicating that the wall-plug efficiency is 2.41% of the DUV LEDs with ascending Al-content chirped SEDL. The mechanism responsible for this improvement is investigated by theoretical simulations. The lifetime of the DUV LED with ascending Al-content chirped SEDL is measured to be over 10,000 h at L50, due to the carrier injection promotion.

… AlGaN-based ultraviolet LEDs, as highly promising solid-… AlGaN-based DUV LEDs have found extensive applications in … broad application prospects of AlGaN-based DUV LEDs, their …

… of the DUV-LED with different types of EBL designs which are reference EBL, conventional superlattice EBL and step-graded superlattice EBL. The analysis of the DUV-LED focuses on …

The photoelectric properties and physical mechanism of AlGaN-based deep ultraviolet light emitting diodes (DUV-LEDs) with the superlattice p-type doping layer (PSL) are studied numerically and compared with the Al-composition (50%) conventional p-type layer AlGaN-based DUV-LEDs. The extraordinary design of DUV-LEDs with varied barrier PSL has been investigated by the advanced physical model of semiconductor device (APSYS) software by comparing the internal quantum efficiency, light output power, electroluminescence intensity, distributions of carrier concentration, and energy band diagrams. As a result of hole injection augmentation and electronic leakage reduction, the property of AlGaN-based DUV-LED with the PSL has been enhanced significantly. Moreover, the 55%-Al-composition of the superlattice barrier p-type doping layer greatly reduces the effective potential height for holes in the valence band, which is beneficial for hole injection from the PSL. The new structure improves the properties of DUV-LED and shows remarkable output performance.

… LEE of DUV-LEDs by introducing a SL hole spreading p-AlGaN … properties of DUV-LEDs for which the SL p-AlGaN contact layer … images for AlGaN DUV-LEDs are compared. This shows …

This study presents a novel approach to mitigate electron overflow in deep ultraviolet (UV) AlGaN light-emitting diodes (LEDs) by integrating engineered quantum barriers (QBs) with a concave shape and an optimized AlGaN superlattice (SL) electron blocking layer (EBL). The concave QBs reduce electron leakage by lowering the electron thermal velocity and mean free path, enhancing electron capture in the active region. The SL EBL further reduces electron overflow without compromising hole transport. At a wavelength of ~253.7 nm, the proposed LED demonstrates a 2.67× improvement in internal quantum efficiency (IQE) and a 2.64× increase in output power at 150 mA injection, with electron leakage reduced by ~4 orders of magnitude compared to conventional LEDs. The efficiency droop is found to be just 2.32%.

… In AlGaN-based DUV-LEDs, electrons in the conduction band and holes in the valence band recombine. This recombination process releases energy as photons in radiative …

This work reports a nearly efficiency-droop-free AlGaN-based deep ultraviolet light-emitting diode (DUV LED) emitting in the peak wavelength of 270 nm. The DUV LED utilizes a specifically designed superlattice p-type electron blocking layer (p-EBL). The superlattice p-EBL enables a high hole concentration in the p-EBL which correspondingly increases the hole injection efficiency into the multiple quantum wells (MQWs). The enhanced hole concentration within the MQW region can more efficiently recombine with electrons in the way of favoring the radiative recombination, leading to a reduced electron leakage current level. As a result, the external quantum efficiency for the proposed DUV LED structure is increased by 100% and the nearly efficiency-droop-free DUV LED structure is obtained experimentally.

This paper reviews the progress of AlGaN-based deep-ultraviolet (DUV) light emitting diodes (LEDs), mainly focusing in the work of the authors’ group. The background to the development of the current device structure on sapphire is described and the reason for using a (0001) sapphire with a miscut angle of 1.0° relative to the m-axis is clarified. Our LEDs incorporate uneven quantum wells (QWs) grown on an AlN template with dense macrosteps. Due to the low threading dislocation density of AlGaN and AlN templates of about 5 × 108/cm2, the number of nonradiative recombination centers is decreased. In addition, the uneven QW show high external quantum efficiency (EQE) and wall-plug efficiency, which are considered to be boosted by the increased internal quantum efficiency (IQE) by enhancing carrier localization adjacent to macrosteps. The achieved LED performance is considered to be sufficient for practical applications. The advantage of the uneven QW is discussed in terms of the EQE and IQE. A DUV-LED die with an output of over 100 mW at 280–300 nm is considered feasible by applying techniques including the encapsulation. In addition, the fundamental achievements of various groups are reviewed for the future improvements of AlGaN-based DUV-LEDs. Finally, the applications of DUV-LEDs are described from an industrial viewpoint. The demonstrations of W/cm2-class irradiation modules are shown for UV curing.

… structures have been proposed for the design of DUV LEDs … Generally, AI mimics human intelligence to identify patterns … This study introduces an AI-driven approach to optimizing DUV …

A mesa-sidewall nanoscale reflective structure was introduced on the p-GaN surface of flip-chip deep-ultraviolet light-emitting diodes (DUV-LEDs) to enhance the light extraction efficiency (LEE). In contrast to conventional planar reflectors, the proposed structure was specifically engineered to not only minimize DUV absorption in the p-GaN layer but also establish what is believed to be a novel reflective pathway for photon propagation. Utilizing an artificial intelligence (AI)-assisted inverse design approach based on the Jaya algorithm, the reflective structure was systematically optimized to maximize the LEE through precise modulation of the light propagation mechanism. A comprehensive investigation into the light extraction process was conducted, revealing the effects of structural parameters on the light propagation path and LEE. Remarkably, both simulation and experimental results demonstrated that the optimized mesa-sidewall nanoscale structure achieved an enhancement of more than 200% in LEE over the conventional Al reflective layer, showcasing its significant potential for high-performance DUV optoelectronic applications. This work provides a viable and efficient strategy for developing high-power DUV-LEDs and demonstrates the potential of AI-driven design in advanced photonic devices.

It is known that light extraction efficiency (LEE) for AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) can be enhanced by using an inclined sidewall of mesa. However, the reported optimal inclined angles are different. In this work, to explore the origin for enhancing the LEE of DUV LED by using inclined sidewalls, we investigate the effect of an inclined sidewall angle on the LEE for AlGaN-based DUV LEDs with different mesa diameters by using ray tracing. It is found that when compared to large-size DUV LEDs with inclined sidewall, the LEE of small-size DUV LEDs with inclined sidewall is enhanced from both the bottom and side surfaces due to the reduced scattering length and material absorption. Additionally, the optimal inclined sidewall angle is recommended within the range of 25°-65°, and the optimal angle for DUV LEDs decreases as the chip size increases. It can be attributed to the fact that there are two scattering mechanisms for the inclined sidewall. For smaller chip sizes, most of the light is directly scattered into escape cones by the inclined sidewall, resulting in a larger optimal angle. For larger chip sizes, the light firstly experiences total internal reflections by the out-light plane and then is scattered into escape cones by the inclined sidewalls, leading to a smaller optimal angle.

AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) suffer from low light extraction efficiency (LEE), primarily constrained by strong optical absorption in the p-GaN layer and total internal reflection (TIR), particularly for the dominant transverse-magnetic (TM) polarization. To address this, we introduce a dual-layer nanostructure design combining surface parabolic cones with embedded p-GaN nanopillars. We demonstrate that conventional layer-by-layer optimization (Strategy A) is limited by inefficient inter-layer mode coupling, whereas our proposed holistic co-optimization (Strategy B) utilizing particle swarm optimization (PSO)-based finite-difference time-domain (FDTD) simulations effectively harnesses the inter-layer synergistic effect. Results reveal that Strategy B boosts the total LEE to 12.98% at 280 nm. Crucially, the TM-mode extraction is enhanced by ∼36-fold (from 0.29% to 10.70%), effectively converting trapped lateral guided modes into upward extracted radiation. This work proves that holistic co-optimization is a necessity for maximizing the performance of coupled multi-parameter photonic devices.

… performance parameters through predictive and optimization strategies; … LEDs. To overcome these issues, this manuscript proposes a method for EBL optimization in AlGaN UV LEDs. …

… structure on the light extraction angle is also pending an in-depth study to prepare better DUV-LED structures … Optimizing light extraction efficiency in inclined sidewall type ultraviolet …

AlGaN-based deep ultraviolet light-emitting diodes (DUV-LEDs), as a novel solid-state ultraviolet light source, compared with the traditional ones, have competitive advantages over traditional UV sources such as mercury (Hg) pollution free, low energy consumption, small size, and tunable wavelengths. They hold broad prospects for development in critical fields including air purification, water disinfection, biosensing, and communications. Enhancing the electro-optical conversion efficiency of DUV-LEDs is essential for achieving large-scale commercial applications in disinfection and sterilization. Improving the device’s relatively low light extraction efficiency (LEE) has proven to be an effective strategy for boosting electro-optical efficiency and overcoming technical barriers. In this review, the fundamental configurations of the AlGaN DUV-LEDs and the regulatory logic of optical polarization characteristics on LEE are summarized. The detailed discussions include the recent research advances in improving the LEE of the DUV-LEDs via optical polarization—specifically by adjusting quantum well structures, optimizing polarization-dependent light propagation paths, and incorporating additional reflection/diffraction structures. Furthermore, it outlines the challenges and development prospects for improving LEE at the optical polarization level.

In order to improve the light extraction for the deep ultraviolet light emitting diodes (DUV-LEDs), the surface microstructure based on a parabola cone array is used and optimized in work. In the optimization of the surface structure, inverse design based on a particle swarm optimization intelligent algorithm is applied to maximize the light extraction. The optimization results show that compared with the traditional planar structure, the optimized surface structure improves the light extraction efficiency by more than 200%. In addition, the influence of the designed surface microstructure on the light propagation is also explored by comparing the light field distribution and the light extraction process with the planar structure DUV-LEDs. It is revealed that the high aspect ratio of an array microstructure can change the light propagation and greatly expand the angle of a light escape cone. This effect can be maximized by the inverse design based on the intelligent algorithm, which has great potential in improving the light extraction of AlGaN-based DUV-LEDs.

Here, we systematically investigate the effect of mesa/sub-mesa sidewall engineering on single-junction (SJ) and high-voltage (HV) deep ultraviolet light-emitting diodes (DUV LEDs). The configuration of ∼46° inclined angle of the mesa/sub-mesa sidewall and Al reflector optimally promotes light extraction of SJ/HV DUV LEDs. We further observe substantial improvements in the self-heating and external quantum efficiency (EQE) droop effects of HV DUV LEDs with an increasing number of sub-mesas. Specifically, the EQE droops are 27.6% and 34.6% for HV DUV LEDs with two and four sub-mesas, respectively, at an input power of 6.4 W. These values are markedly lower than the 51.6% droop observed in the SJ DUV LEDs, which is partly attributed to the superior heat dissipation and light extraction facilitated by a high perimeter-to-area ratio of the sub-mesas. This investigation sheds light on mesa design-related efficiency droop behaviors and contributes to enhancing the optoelectronic performance of AlGaN-based DUV LEDs.

The current low external quantum efficiency (EQE) of deep ultraviolet (DUV) LEDs and micro-LEDs is largely attributed to their low light extraction efficiency (LEE). To address this issue and increase the LEE of DUV devices, various strategies such as reducing size, modifying surface with nanostructures and roughening substrates have been proposed. While some studies have investigated the effects of nanopillar and size on DUV LED, there remains a lack of systematic research on the LEE enhancement mechanism across different wavelengths and sizes of DUV LEDs, micro-LEDs, and nano-LEDs. Therefore, in this study, we employed the numerical simulation method to explore the LEE, near-field intensity distribution, and far-field light intensity distribution from various angles for DUV LEDs, micro-LEDs, and nano-LEDs with wavelengths of 255 nm, 260 nm, and 275 nm, respectively. Our findings reveal a significant improvement in the LEE of DUV nano-LEDs and micro-LEDs, accompanied by reduced divergence angles. Moreover, we observe that longer wavelengths correspond to higher LEE values for devices with similar size. This enhancement in LEE is attributed to factors such as increased sidewall emission and reduced p-GaN absorption. Our investigation indicates that as the size of the DUV device decreases, the sidewall LEE for both transverse electric (TE) and transverse magnetic (TM) modes increases, with TM mode exhibiting a larger enhancement. This enhancement is mainly attributed to the reduction of total reflection within the DUV LEDs and micro-LEDs resulting from size reduction. Despite this, TE mode remains the main contributor to overall LEE. Additionally, our study reveals a reduction in p-GaN absorption of DUV light with decreasing device size, further contributing to the enhancement of LEE in DUV micro-LEDs and nano-LEDs. The increased LEE and reduced divergence angles of small-size DUV micro-LEDs and nano-LEDs not only promote lower power consumption but also enable easier optical system coupling. Consequently, these advancements have significant potential in optical wireless communication, charge management and high-precision lithography.

… 365 nm UV curing to 280 nm DUV disinfection. Nevertheless, … This work presents the TCAD-based design and simulation of … epitaxial architecture of the vertical GaN/AlGaN MQWs …

The long-term stability of ultraviolet (UV)-C light-emitting diodes (LEDs) is of major importance for many applications. To improve the understanding in this field, we analyzed the degradation of AlGaN-based UVC LEDs and modeled the variation of electrical characteristics by 2D simulations based on the results of deep-level optical spectroscopy (DLOS). The increase in the forward leakage current observed during ageing was ascribed an increase in trap-assisted tunneling. The analysis of the degradation kinetics suggests the role of a defect diffusion process, possibly involving impurities coming from the p-type layers.

We investigate the degradation physics of AlGaN-based UV-C LEDs emitting at 265 nm, by combined experimental measurements and numerical simulations. We demonstrate that: (i) during long-term operation, devices show degradation in the optical emission, which is more prominent at low measuring current levels; (ii) a strong correlation was found between the emission decrease and the increase in the forward leakage current, which suggests that the same process is responsible for the electrical and optical degradation; (iii) the observed long-term optical degradation was reproduced by numerical simulations, as being due to the increase in the defect density in the QW during the ageing, demonstrating the impacting role of SRH recombination on device reliability. (iv) The degradation kinetics follow the square-root of stress time. By solving Fick’s differential equation near the quantum well, we ascribed degradation to the out-diffusion of hydrogen from the quantum well region, leading to the activation of non-radiative recombination centers, through the de-hydrogenation of point-defects.

… doping on the degradation behaviors of DUV-LED still … the epitaxial layer, low Mg doping efficiency in p-AlGaN layer, … previously suggested by TCAD simulation. Region (ii) represents …

This study provides an in-depth analysis of the performance of GaN substrate-based MicroLEDs with different epitaxial structures using Silvaco TCAD. The focus is on exploring how variations in Al content in the electron blocking layer, In content in the quantum well layers and doping concentration in $p-\text{GaN}$ affect device performance. The results show that changes in these epitaxial structures impact key metrics such as threshold voltage, wall plug efficiency, internal quantum efficiency, and the ideality factor. These findings offer valuable insights for designing high-performance GaN substrate-based MicroLEDs.

The serious electron leakage and poor transport of hole injection layers in deep‐ultraviolet (DUV) light‐emitting diodes (LEDs) lead to an imbalance between the hole and electron currents, which reduces the device's performance. Herein, a new DUV LED structure is designed. The aluminum composition of the p‐type electron‐blocking layer (p‐EBL) gradually decreases from 0.95 to 0.75 along the growth direction, replacing the traditional bulk p‐EBL. When the injection current is 100 mA, the optical power of this structure is about 32% higher than that of the traditional structure. In addition, when the p‐EBL adopts the opposite gradient (the Al composition gradually increases from 0.75 to 0.95), the device performance suddenly drops dramatically. The related devices are simulated by Silvaco TCAD software. The results show that the performance outputs of the two opposite aluminum gradient growth modes are completely opposite. The proposed p‐EBL with a gradual step‐down Al composition along the growth direction helps to improve the efficiency of hole injection into multiple quantum wells (MQWs) and reduce the level of electron leakage. This work provides an effective solution for increasing the light output power of high‐performance DUV LEDs.

Optimizing the strain level within n-AlGaN contact layer is crucial for achieving high-efficiency deep ultraviolet light-emitting diodes (DUV-LEDs). In this study, a step doping strategy in n-AlGaN containing a lightly-doped bottom layer and a heavily-doped upper layer was proposed. The introduction of the lightly doped bottom layer mitigates issues such as strain accumulation and defect generation associated with heavily-doped n-AlGaN which traditionally impairs epitaxial quality and electrical performance of DUV-LEDs, even though similar dislocation density was identified between two LED samples. Thanks to the more uniform distribution of electron concentration and radiative recombination rate in the quantum well region, DUV-LEDs with step-doped layer exhibits 40% higher light output power compared with traditional structure. This work underscores the potential of doping engineering in advancing the performance of DUV-LEDs.

The lifetime of deep-ultraviolet light-emitting diodes (LEDs) is still limited by a number of factors, which are mainly related to semiconductor defects, and still need to be clarified. This paper improves the understanding of UV LED degradation, by presenting an analysis based on combined deep-level transient spectroscopy (C-DLTS), electro-optical characterization, and simulations, carried out before and during a constant current stress test. The original results of this paper are (i) C-DLTS measurements allowed us to identify three traps, two associated with Mg-related defects, also detected in the unaged device, and one related to point defects that were generated by the ageing procedure. (ii) Based on these results and on TCAD simulations, we explain the variation in the forward I–V by the degradation of the p-contact, due to Mg passivation. (iii) On the other hand, optical degradation is ascribed to an increase in defectiveness of the active region and surrounding areas, which led to a decrease in injection efficiency, to an increase in non-radiative recombination, and to an increase in trap-assisted tunneling processes.

We report on the illustration of the novel electron blocking layer (EBL) free AIlnN nanowire light-emitting diodes (LED) with a single-quantum well (SQW) operating in the deep ultraviolet (DUV) wavelength region (sub-250 nm). We have systematically analyzed the results using Atlas TCAD and compared them with simulated AIGaN nanowire DUV LED. From the simulation results, a significant efficiency droop was observed in AIGaN LED, attributed to the significant electron leakage. However, compared to AIGaN nanowire DUV LED at a similar emission wavelength, the proposed (SQW) AIlnN- based light-emitter offers higher internal quantum efficiency without droop up to the current density of 1500 A/cm2 and high output optical power. Further research shows that the performance of the AIlnN DUV nanowire LED reduces with multiple QWs in the active region due to the presence of the non- uniform carrier distribution in the active region. This study provides important insights into the design of a new type of high- performance AIlnN nanowire DUV LED, by replacing currently used AIGaN semiconductors.

In this paper we investigate the reliability of AlGaN-based UV-C LEDs with an emission wavelength of 265 nm. By submitting the devices to constant current stress, two main electrical degradation processes are identified: a turn-on voltage shift and an increase in the forward leakage current. In particular, these processes were respectively attributed to: (i) a partial passivation of the Mg-doping concentration in the region adjacent to the contact, probably caused by a local hydrogen diffusion, and ii) a diffusion/generation process of defects in the interlayer, responsible for the increase in the trap-assisted tunneling. To validate these hypotheses, we employed TCAD simulations by varying only the Mg-doping concentration in the region adjacent to the p-contact and the defect density in the interlayer. Thus, we correctly reproduced the experimental variation in electrical characteristics, confirming the physical mechanisms identified.