Metalorganic chemical vapour deposition of junction isolated GaAlAs/GaAs LED structures

Abstract

A low-cost high-radiance Ga 1− x Al x As/GaAs LED has been developed using p-n junction isolation to achieve current confinement in an inverted Burrus LED structure. Junction isolation avoids the use of proton implantation techniques leading to a simplification of the device fabrication process. Using this structure devices with a high internal quantum efficiency of 87% which launch up to 1.5 mW into 200 μm, 0.3 nA fibre at 150 mA and have rise and fall times of less than 5 ns, have been fabricated. MOCVD was carried out in a computer-controlled atmospheric pressure system with vent-run manifold and a horizontal geometry reactor. The LED structure involved a two-stage growth process in which initially an n-type isolation layer was grown on a p-type substrate, followed by infill growth, through contact holes, of the inverted LED structure. In this paper we will describe in detail the growth and preparation of the optimised junction isolated LED structure, including growth rate and composition control, layer uniformity and deliberate interface grading. Exploration of the use of magnesium doping and triethylaluminium for precise control of active layer doping and composition will be discussed and finally details of device characteristics and performance are presented.