Effects of an InGaN prelayer on the properties of InGaN/GaN quantum well structures

In this paper we report on the effects of including of an InGaN prelayer in an InGaN/GaN multiple quantum well (MQW) structure. Two equivalent 10 period In_0.16Ga_0.84N MQW structures were studied, one with a 24 nm thick In_0.05Ga_0.95N prelayer, one without. X-ray diffraction measurements showed no evidence of strain relaxation in the structure containing the prelayer, while AFM revealed a 15% increase in average diameter of "V"-defects. Temperature dependent photoluminescence (PL) showed the MQW structure, with the prelayer, to exhibit a higher room temperature internal quantum efficiency than the reference structure. PL excitation spectroscopy revealed an absorption and carrier transfer process associated with the InGaN prelayer, which created an additional recombination pathway resulting in a feature on the high energy side of the PL spectrum. Time-resolved PL studies showed that this recombination had a weaker temperature sensitivity to that of the primary luminescence feature, and thus may be responsible for the enhanced PL intensity measured at 300 K. Monochromatic cathodoluminescence (CL) images showed the high energy feature originated from the "V"-defects. It is thus suggested that the InGaN prelayer may provide a transfer mechanism for carriers in the prelayer into the semi-polar QWs on the "V"-defect facets. Alternatively the high energy emission may arise from QWs at the base of the stack that have parameters that are significantly different from the rest of the QWs.