Confocal microscopy study on spatial variation of photoluminescence in blue-emitting InGaN/GaN MQWs with different growth parameters

Scanning confocal microscopy is used to study blue-emitting Indium Gallium Nitride (InGaN)/Gallium Nitride (GaN) multi-quantum wells grown by metal-organic chemical vapor deposition under different growth conditions. Sub-micrometer scale spatial and spectral variation of photoluminescence (PL) has been observed. Spectrum measurement shows the PL peak in bright region is red-shifted comparing with that in dark region, and that the peak intensity of bright region is at least twice as strong as that of dark region. Images show defect luminescence features which are about 500 nm in diameter and have PL peak at around 550 nm. Experiments show that reducing In/Ga ratio, increasing growth pressure and increasing NH₃ flow rate can all increase the localization effect and result in the increase of sample average PL intensity. Moreover, average PL intensity increases with the increasing of bandgap difference and PL peak intensity difference between bright and dark regions in PL.