Strain-induced compositional fluctuation and V-defect formation in green-InGaN/GaN multi-quantum wells grown on sapphire and freestanding GaN substrates

Spatial variation of V-defects and emission characteristics of green-InGaN/GaN multiple quantum wells (MQWs) grown on sapphire and freestanding GaN substrates have been studied. Near-field scanning microscopy exhibits uniformly distributed nanoscale bright spots with a single emission wavelength for MQWs grown on freestanding GaN, whereas, the nanoscale spots get accumulated resulting in large bright areas of micron scale with fluctuated emission wavelengths in case of sapphire. Homoepitaxially grown MQWs reveal large area uniformity in cathodoluminescence emission but a large contrast is observed for sapphire case.