Suppression of non‐radiative effects in AlGaN through nanometer scale compositional inhomogeneities

Abstract

UV light emitting diodes (UVLEDs) emitting at wavelengths shorter than 365 nm remain in the research and development stage, with external quantum efficiencies and device operating lifetimes well below that of commercially available blue LEDs. These limitations are partially attributable to the large density of dislocations in these devices that arise due to heteroepitaxial growth of high AlN mole fraction III‐Nitride semiconductors and act as non‐radiatve recombination centers that reduce efficiency and increase debilitating heating. An approach to mitigating this problem is to incorporate nanometer scale compositional inhomogeneities within the AlGaN (NCI‐AlGaN) active region of a UVLED that can enhance the internal quantum efficiency by concentrating carriers within regions of narrow bandgap surrounded by a wider band gap matrix. In this paper we report on the growth and characterization of NCI‐AlGaN alloys deposited by plasma‐assisted molecular beam epitaxy. Growth under N‐limited and nearly stoichiometric growth conditions promote the spontaneous formation of these NCI regions. This is attributed to lower adatom mobility of group III and N species on the AlGaN layer surface under these conditions as well as the formation of beneficial surface faceting. Optical characterization by both temperature dependent, time‐resolved and time‐integrated photoluminescence demonstrates the capability for NCI regions to suppress non‐radiative recombination in these active regions despite the presence of a large density of defects. However, reduction of the defect density, both dislocations and impurities, improves the performance of these active regions. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)