Physics of Textured III-Nitride Quantum Wells for Applications to LEDs

Abstract

Summary form only given. In this paper we report the growth of GaN/AlGaN MQWs by MBE on atomically-smooth (0001) GaN templates and (0001)-oriented GaN templates with random surface texture. We show that this approach of employing nanotextured surfaces and wrinkled QWs leads to the improvement of both the internal quantum efficiency as well the extraction efficiency. AFM studies show that the MQWs replicate the texture of the GaN template. The PL and CL spectra from the smooth MQWs are red shifted and those of the textured MQWs are blue shifted with respect to the bulk GaN spectrum. These results are consistent with a reduction of polarization-induced electric fields in the parts of the textured MQWs which are not perpendicular to the [0001] polar direction. Furthermore, the PL intensity from the textured QWs, with well widths 7nm, was found to be about 700 times higher than that from similarly produced MQWs on smooth GaN templates. This significant enhancement in the PL intensity from the textured MQWs is attributed partly to the enhancement in light extraction efficiency and partly to the enhancement in internal quantum efficiency. One obvious source for the increase in internal quantum efficiency in the textured MQWs is the reduction of the quantum confined stark effect (QCSE) since the majority of the planes of the MQWs are not perpendicular to the polar direction. An additional source for the increase in internal quantum efficiency is the enhanced spontaneous emission at the wedges of intersecting planes of QWs, where they form quantum wire-like structures. These conclusions are supported by spot CL measurements taken in regions with different surface orientations. The employment and benefits of such textured MQWs in III-Nitride LEDs is discussed