Influence of residual oxygen impurity in quaternary InAlGaN multiple-quantum-well active layers on emission efficiency of ultraviolet light-emitting diodes on GaN substrates

Abstract

The influence of residual impurities in quaternary InAlGaN active layers on the emission efficiency of 350nm band ultraviolet light-emitting diodes on GaN substrates has been investigated. Secondary ion mass spectrometry and capacitance-voltage measurements have revealed that a large amount of oxygen is incorporated into the InAlGaN active layers owing to relatively low growth temperatures for Al-content epitaxial films. The increase of the InAlGaN growth temperature from 780to830°C results in both the residual oxygen level decrease from 1×1018to4×1017cm−3 and the output power improvement from 0.6to2.6mW at 100mA. It is also found that devices containing lower oxygen concentration in the InAlGaN active layers demonstrate a higher electroluminescence intensity ratio of the band-edge emission from the well layers to the donor-acceptor-pair emission from the p-type layers at low temperatures. These experimental results, in conjunction with numerical calculations, suggest that the reduction in the oxygen impurity level in the InAlGaN active layers has an effect on suppressing the electron leakage current into the p-type layers, and thus improving the internal quantum efficiency of InAlGaN-based ultraviolet light-emitting diodes.