Defect Reduction in GlGaN/GaN Ultra-Violet Photodetectors.

摘要

Since the native substrates are not easily available in sufficient size and quantity, alternative methods by using various types of buffer layers to isolate the films from the deleterious effect of the substrate have been investigated. In the case of MOCVD, a thin GaN or AlN film grown at low temperature ((caret)500 o C) is commonly used as the buffer layer for the active layer growth at much higher temperatures. The other buffer layers such as the low temperature InN layer on sapphire A-face, double low temperature AIN or GaN layers between high temperature grown GaN, GaN/AIGaN superlattices, and the SiO2 patterned GaN/AIN buffer on SiC substrate (the lateral growth) were all investigated to improve the epilayer quality. Recently, the effect of the growth rate, the thermal annealing, and the impurity doping of buffer layers were also reported. As compared to MOCVD growth, much fewer investigations were reported for MBE. In the latter case, an AIN buffer layer is commonly used as the buffer layer and a high growth temperature ((caret)900 o C) may lead to a better epilayer quality. The nitridation temperature of sapphire substrate and the Ill/V flux ratio were found to have an impact on the GaN quality.