Persistent photoconductivity in InGaN/GaN multiquantum wells

Abstract

Optical properties of undoped InGaN/GaN multiquantum wells (MQWs) have been investigated by photoconductivity, photoluminescence, and photoluminescence excitation measurements. We report the observation of persistent photoconductivity (PPC) in InGaN/GaN MQWs and show that the PPC effect arises from In composition fluctuations in the InGaN well layer. From the analysis of the decay kinetics, the localization depth caused by composition fluctuations has been determined. Compared with the results of complementary absorption and photoluminescence measurements, it is found that the quantum-confined Stark effect due to piezoelectric field and composition fluctuations both exist in the InGaN/GaN MQWs. These two effects are responsible for the photoluminescence Stokes’ shift in the InGaN well layers. Here, we provide a unique way to distinguish the individual contribution to the Stokes’ shift for the piezoelectric field and composition fluctuations.