A study on the reverse-bias and ESD instabilities of InGaN-based green LEDs

摘要

Over the last years, important efforts have been done in order to understand the degradation mechanisms of GaN-based LEDs submitted to forward-bias stress tests. On the other hand, only little work has been done to understand the degradation of LEDs submitted to reverse-bias stress. However, this topic is of high interest, since (ⅰ) the reverse-bias robustness of the LEDs is strongly correlated to their stability under Electrostatic Discharge (ESD) events and (ⅱ) the analysis of the reverse-bias degradation can provide important information on the role of high electric fields and reverse current in limiting the reliability of the LEDs.rnTherefore the aim of this paper is to describe a detailed investigation on the reverse-bias degradation of GaN-based LEDs. The results described in this paper indicate that: (ⅰ) under reverse bias, LEDs can show a weak luminescence signal, due to the recombination of carriers injected in the quantum-wells; (ⅱ) reverse-bias stress can induce the degradation of the electrical characteristics of the LEDs (increase in reverse-current, decrease in breakdown voltage), due to the generation of point defects in proximity of pre-existing defective regions. (ⅲ) Furthermore, our tests indicate that the defective regions responsible for reverse-current conduction can constitute weak points with respect to ESD events: ESD failures are determined by the shortening of the junction in proximity of one of the defective sites responsible for reverse-current conduction.