Optimization of Electroluminescent Efficiencies for Vapor-Grown GaAs[sub 1−x]P[sub x] Diodes

Abstract

A series of diodes have been prepared by a vapor‐phase growth technique to investigate the effects of current‐spreading, absorption, impurity concentrations, and alloy composition on room‐temperature electro‐luminescent efficiencies. It is shown that for maximum efficiencies, a diode structure should be prepared with a p+ surface layer to enhance current spreading, and a "window" containing about 10% more than the p‐n junction region to reduce absorption losses. It is also shown that the most efficient radiative recombination originates on the p‐side of the junction; low acceptor concentrations and high donor concentrations which are required for strong electron injection into the p‐side of the junction are thus found to result in highest electroluminescent efficiencies. Slow compositional grading between the substrate and the p‐n junction also resulted in increased efficiencies. A drop‐off in efficiency near the direct‐indirect transition for values of increasing from 0.38 was found to be severe, however, a corresponding increase in the spectral sensitivity of the eye was found to provide a broad maximum in diode brightness at emission wave‐lengths near 6800Aå (). Planar uncoated diodes have provided brightness values in excess of 300 ft‐L at 10 amp/cm2 with external efficiencies of at 6400Aå. Plastic encapsulants ean be readily used as domes to increase external efficiencies by a factor of 3, or as directional lenses to provide beam‐widths as narrow as 7°.