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We studied the electrical and optical properties of 276 nm and 306 nm AlGaN-based ultraviolet light emitting diodes (UV-LEDs) in the temperature range of 303–403 K. Capacitance–voltage measurements were performed to extract the carrier distribution in UV-LED, especially around the multi-quantum well structure. Our results showed that an additional carrier concentration peak close to the first quantum well of the p-n junction was present at elevated temperatures. Our physical simulation 276 nm LEDs revealed the cause of the concentration change to be the higher stress of the barrier layer with the temperature increase which introduced additional piezoelectric charge at the heterostructure interfaces. It is also found that the electron barrier layer (EBL) acceptor concentration decreased with the temperature, which caused a shift in the carrier concentration peak position, corresponding to higher EBL contribution to the increase of depletion width in the UV-LED. Higher temperatures lead to the increase of polarization charge at the quantum barrier/EBL interface, associated with downward bending of the conduction band of the quantum barrier, which is possibly the reason for an additional carrier concentration peak. The variation of the carrier distribution in UV-LED with temperature provides a new perspective and method to explain the UV-LED thermal droop effect. [ABSTRACT FROM AUTHOR]

Thermal droop, i.e., the loss of emission efficiency over a certain temperature range, is an important performance bottleneck for the successful commercial application of deep-ultraviolet light emitting diodes. In this study, we examined the mechanism of two thermal droop processes of 255 nm AlGaN quantum well light emitting diodes under temperature stresses in order to obtain steady optical output in a broad temperature range. We discovered that the increase in leakage current in the low forward bias region is accompanied by a decrease in apparent carrier concentration of quantum wells near the p side during the thermal droop process at high temperature (>300 K), indicating that the activation of thermal defects enhances the trap assisted tunneling effect and causes the optical power to decrease more significantly at low current. Compared with normal temperature, the low emission power at low temperatures is attributed to the minority trap H1, which has an activation energy of 0.527 eV at 190 K, according to deep level transient spectrum analysis. At low temperatures above 175 K, the optical power increases as the temperature rises due to enhanced hole injection. By analyzing the droop characteristics, we concluded that the activation of thermal defects is the most probable cause of high temperature thermal droop in 255 nm AlGaN quantum well light emitting diodes, whereas hole trap H1, which is linked to gallium vacancy complexes related defects, is most likely the source of low temperature thermal droop. [ABSTRACT FROM AUTHOR]

We report the degradation study on AlGaN-based 265 nm ultraviolet light-emitting diodes (UV-LEDs) under a series of constant current stress. The failure mechanisms were investigated systematically by measuring the optical and electrical characteristics of the LEDs before and after aging. The variation of carrier concentration in the active region was analyzed by capacitance–voltage. Combining the extracted apparent charge distribution profiles with the simulation results of the devices before and after the stress, we found that the change of carrier concentration in the multiple quantum wells was related to the donor diffusion on the n-side. On the p-side, both the acceptor concentration of electron blocking layer (EBL) and the defects in p-GaN contact layer were also found to be under constant change. The reduction of the EBL doping concentration has contributed to an increase of the diode depletion width during the stress. The changes in the LEDs before and after stressing indicate a compensating effect occurred in the p-type EBL close to the quantum wells, which leads to the degradation of the optical power of the 265 nm UV-LEDs. [ABSTRACT FROM AUTHOR]

By using the sol-gel spin-coating method, La-InZnO films with different La (0 at%, 2 at%, 4 at%, and 6 at%) doping concentrations were grown on p-GaN / sapphire film templates, and self-driven p-GaN / n-ZnO heterojunction ultraviolet (UV) detectors were prepared. The effects of La doping concentration on the microstructure, optical, and electrical properties of synthesized La-InZnO films were studied. In addition, the optical sensing characteristics and photoelectric response performance of four p-n heterojunction UV detectors were compared. La doping can decrease the content of oxygen vacancies. It also reduces the carrier concentration and mobility of the films. At zero bias voltage, the 2 at% doped device has the best performance, with a peak responsivity of 46 mA/W at 366 nm, a high spectral selectivity full width at half maximum (FWHM) of only 6.92 nm, and a fast response with the rise and decay times of 1.15 ms and 2.42 ms, respectively. This study demonstrates a feasible method for improving the performance of self-driven heterojunction UV detectors. • Simple and easy to prepare large area by sol-gel method. • n-ZnO/p-GaN heterojunction detector can operate without external power supply. • Lanthanide doping can improve detector responsiveness and spectral selectivity, and reduce response time. • 2 at% of lanthanum doping is the optimal doping concentration. [ABSTRACT FROM AUTHOR]