Identification of the Kirkendall effect as a mechanism responsible for thermal decomposition of the InGaN/GaN MQWs system

Abstract

Abstract A drop in the efficiency of light-emitting diodes based on InGaN/GaN QWs known as the ‘green gap’ has been studied intensively over the past dozen years. Several factors were revealed to contribute to its origin, such as random fluctuations in the indium concentration or the diffusion of point defects during the growth of QWs. The aim of this paper is to demonstrate that the Kirkendall effect can be the mechanism responsible for the thermal decomposition of InGaN/GaN MQWs structures, contributing to the green gap problem. By applying density functional theory, harmonic approximation, and harmonic transition state theory, we calculated the heights of the migration energy barriers of In and Ga atoms diffusing in I n x G a 1 − x N alloys ( x = 0 , 0.11 , 0.22 ), the vibrational frequencies of I n x G a 1 − x N alloys in the presence of migrating point defects, the temperature dependencies of the defect migration energy barriers and diffusion coefficients of Ga and In atoms migrating in I n x G a 1 − x N alloys. We demonstrated the presence of unbalanced diffusion rates of In and Ga atoms at the I n x G a 1 − x N / G a N interfaces and finally explained the experimentally observed mechanism of void formation at the I n x G a 1 − x N / G a N interfaces by means of the Kirkendall effect.