Effect of graded Al content in the last quantum barrier on the luminescence properties of ultraviolet InGaN/AlGaN multiple quantum wells

Abstract

In this paper, the influence of graded Al content in the AlGaN last quantum barrier (LQB) on the luminescence properties of ultraviolet light-emitting InGaN/AlGaN multiple quantum wells (MQWs) is investigated. The average Al content in the AlGaN LQB is the same for all samples, but the distributions of Al content are different from each other. It is found that in the Al-content-graded LQB where the Al content decreases along the growth direction, a potential well for holes and a potential barrier for electrons can be formed simultaneously, causing an enhanced injection of holes and a better confine of electrons, respectively. As a result, the luminescence intensity can be improved. However, on the contrary, if the Al content in LQB varies in an inverse way, the luminescence efficiency is reduced. This can be ascribed to the inhibited hole injection as well as the increased electron leakage, as the hole barrier and electron well may be formed in LQB, where the Al content increases along the growth direction.