Interface modification of the InGaN/GaN quantum wells: the strain pre-relief effect.

Interface modification by inserting an ultrathin low-temperature GaN layer prior to the growth of high-temperature GaN barriers followed by an annealing process was employed to improve the properties of the InGaN/GaN quantum wells. By detailed studies and comparisons of the surface morphology, photoluminescence and the surface compositions of the InGaN/GaN quantum wells at different growth stages with and without the interface modification, we find that with the interface modification the surface morphology was significantly improved with better smoothness, and smaller and shallower pits of lower density compared with that without interface modification; further, the indium aggregation and phase separation were suppressed. The physical phenomena are attributed to the 'strain pre-relief effect' by the formation of quasi-dots (approximately 20 nm in diameter) prior to temperature ramping and growth of high-temperature GaN barriers. Furthermore, the ultrathin low-temperature GaN layers have a good protection property as confirmed by PL and XPS measurements.