Two-dimensional confocal photoluminescence spectroscopy of nonpolar a-plane InGaN/GaN multiple quantum wells

A nonplanar a-plane (11–20) and c-plane (0001) InGaN/GaN multiple quantum wells (MQWs) structures were grown an r-plane (1–102) and a c-plane (0001) sapphire (Al₂O₃) substrate, respectively. Using two-dimensional confocal photoluminescence spectroscopy, the spatially resolved optical characteristics of two samples are examined. We found that the integrated PL intensity of a-plane MQWs is 88.4% greater than that of c-plane MQWs based on our analysis of PL spectra taken at room temperature. According to results from two-dimensional confocal PL mapping, the a-plane MQWs have a more uniform distribution of PL intensity according to two-dimensional space than the c-plane MQWs. Compared to typical c-plane InGaN/GaN MQWs, the experimental results of the two-dimensional confocal PL peak position distribution and PL spectrum skewness map of nonpolar a-plane InGaN/GaN MQWs show increased uniformity of the InGaN alloy in two-dimensional space and a decreased proportion of multiple PL peaks buried in the PL spectrum. These findings are ascribed to higher electron and hole wavefunction overlap caused by decreased the quantum-confinement Stark effect and increased the uniformity of InGaN alloy in the two-dimensional space of nonpolar a-plane InGaN QW.