Carrier localization degree of In0.2Ga0.8N/GaN multiple quantum wells grown on vicinal sapphire substrates

Abstract

In this work, we have grown In0.2Ga0.8N/GaN multiple quantum well (MQWs) epitaxial structure on vicinal sapphire substrates by low pressure metal-organic chemical vapor deposition and investigated the relationship between carrier localization degree and vicinal angles of sapphire substrates. The optical analysis confirmed that the In0.2Ga0.8N/GaN MQWs grown on 0.2°-off sapphire substrate exhibited the smallest carrier localization degree and more ordered In0.2Ga0.8N/GaN MQW structure. In addition, mechanisms for carrier localization in In0.2Ga0.8N/GaN MQWs grown on vicinal substrate were discussed based on the results obtained from the power and temperature dependent photoluminescence measurements. The Raman spectrum showing the in-plane compressive stress of the GaN epitaxial structures grown on vicinal sapphire substrates revealed the relation between the dislocation density and the carrier localization degree in MQWs. From transmission electron microscopy images, the threading dislocation density (TDD) of In0.2Ga0.8N/GaN MQWs grown on 0.2° vicinal sapphire substrate at the bottom of n-GaN layer was about 9.4×108 cm−2 and reduced to 3.0×108 cm−2 at the top of n-GaN layer. We also obtained the TDD of 5.6×107 cm−2 in the MQW region and only 1.0×107 cm−2 in the p-GaN region. Based on the results mentioned above, 0.2°-off substrate can offer In0.2Ga0.8N/GaN MQW blue light-emitting diode structures with benefits, such as high crystal quality, low defects, and small carrier localization degree.