Stability and degradation of AlGaN-based UV-B LEDs: Role of doping and semiconductor defects

Within this paper, we present an extensive analysis of the degradation of UV-B light-emitting diodes (LEDs) submitted to constant current stress. The study is based on combined electrical, optical and spectral characterization, and capacitance deep-level transient spectroscopy (C-DLTS). The results of this analysis demonstrate that the decrease in the optical power during the stress is stronger at low measuring current levels, indicating that the degradation is related to the increase in Shockley-Read-Hall (SRH) recombination. The electrical characterization shows a decrease in the driving voltage, probably due to an increased activation of the Mg dopant, and an increase in the sub-threshold forward current, that suggest a generation of mid-gap states during the stress. C-DLTS measurements were carried out to study the variation in defects concentration after stress; the most relevant traps were ascribed to the presence of Mg doping and/or to intrinsic defects related to the GaN growth.