Effect of annealing on optical properties of InGaN/GaN multiple quantum wells

Abstract

Site-selective photoluminescence, photoluminescence excitation, and time-resolved luminescence in as-grown and thermally treated In0.15Ga0.85N/ GaN multiple quantum wells (MQWs) was investigated as a function of well width in the temperature range of 10-300 K. Thermal annealing at 800 • C for 30 min monitored by microstructure imaging was shown to result in an alteration of MQWs optical properties intricately depending on the well thickness.The observed blue shift of the luminescence band and pronounced changes in the absorbance indicate a remarkable interdiffusion of indium at the quantum well-barrier interface for MQWs with thin (2 nm) wells.Meanwhile for thicker (3 nm) wells, a pronounced red shift of the luminescence band and an increase in the luminescence decay time was observed and attributed to electron-hole wave function separation facilitated by the smoothened band potential profile.In the thickest wells (4 nm), annealing resulted in even more pronounced improvement of microstructure, which led to a noticeable reduction of the localization energy of the electronic excitations (an annealing-invoked luminescence peak blue shift that overweighs the red one caused by intrinsic field) and to suppression of nonradiative recombination (an increase in luminescence efficiency).The results are accounted for in terms of annealing-invoked In-Ga interdiffusion, which behaves as either diffusion of indium to barriers or "uphill" diffusion within the wells depending on the well width.