Origin of multiple peak photoluminescence in InGaN/GaN multiple quantum wells

Abstract

Optical spectroscopy has been performed for a set of In0.12Ga0.88N/GaN multiple quantum wells (MQW) grown by metalorganic vapor phase epitaxy at 820 °C. Time-resolved, temperature- and power-dependent photoluminescence as well as spatially-resolved cathodoluminescence measurements have been applied to elucidate the nature of the recombination mechanisms responsible for the radiative transitions in the samples. The photoluminescence spectra in this set of samples are dominated by strong multiple peak emissions associating with both confined levels of the MQW system (the higher energy band) and with strongly localized states of energies much lower than the QW band gap. We suggest that the photoluminescence originate from (i) the MQW exciton recombination, (ii) excitons localized in the quasidot regions with indium concentrations higher than in the alloy due to segregation processes, and (iii) from localized states in zero-dimensional quantum islands created by surface defects such as pits and V defects. Buried side-wall quantum wells caused by V defects might also influence the photoluminescence spectra.