Abstract
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.
Highlights
Deep ultraviolet (DUV) light-emitting diodes (LEDs) based on AlGaN in the range of 200–280 nm (UV-C) are of high interest for several applications, including water purification and recycling, disinfection of medical equipment and food, UV curing, and plant growth lighting, due to their advantages of small size, low energy consumption, fast switching and preheating time[1,2,3,4,5]
The defect behaviors in the degradation of the AlGaN based UV-C LEDs under constant current stress were systematically studied by Wang et al, who found that the degradation was mainly derived from the generation of VGa in the Si-doped region, as both the reduction of the output optical power (OP) and the increase in the reverse current were linearly related to the increase in VGa[19]
The LEDs were stressed with the currents from 40 mA, 60 mA, 80 mA and 100 mA, which are in the cuLroraednintgd[MenasthiJtyaxr]a/janxg/oeubtpeuttw/Ceoemnm3o2nH.7TManL/dfo8n1ts./6TeAX//cfomnt2d.aOtau.jsr current densities were consistent with other many studies and degradation curves were divided into catastrophic degradation and gradual degradation stages
Summary
Deep ultraviolet (DUV) light-emitting diodes (LEDs) based on AlGaN in the range of 200–280 nm (UV-C) are of high interest for several applications, including water purification and recycling, disinfection of medical equipment and food, UV curing, and plant growth lighting, due to their advantages of small size, low energy consumption, fast switching and preheating time[1,2,3,4,5]. The epitaxial growth conditions of AlGaN on the AlN buffer layer result in a relatively high density of point defects, such as III-V gallium vacancies, aluminum vacancies and nitrogen vacancies (VGa, VAl, VN ) or hydrogen and carbon impurities[11,12,13,14], which will become Shockley-ReadHall (SRH) recombination centers in the active region of the device and lead to lower internal quantum efficiency (IQE)[15, 16]. The degradation of AlGaN-based multiple-quantum wells (MQWs) at 265 nm UV-C LEDs stressed by different constant currents (40 mA, 60 mA, 80 mA, 100 mA) was studied extensively, which could reveal detailed information on the nature of the operation current density involved in the degradation process. Combining capacitance voltage (C-V) measurements with simulations before and after different currents stress provide the information on the change of carrier concentration of the active region and electron blocking layer (EBL) with respect to depth
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