Green and blue emissions in phase-separated InGaN quantum wells

Abstract

We have investigated temperature-dependent photoluminescence (PL) of green and blue light-emitting InGaN/GaN multiple quantum wells at different excitation powers. Two InGaN-related PL peaks centered at around 2.4 and 2.7 eV are assigned to quasi-quantum dot (QD) emissions (PD) and the InGaN matrix emission (PM), respectively, due to a strong phase separation confirmed by high-resolution transmission electron microscopy. In contrast to the S-shaped temperature-dependent behavior of the PM peak energy, the PD peak energy initially decreased and then increased with increasing temperature up to 300 K, indicating that the carriers within QDs relax to stronger localized states first and then are thermalized to higher levels with increasing temperature. Interestingly, it was found that with increasing temperature both the emission intensities initially increased and then decreased. This behavior was attributed to an increased carrier localization effect and then enhanced non-radiative recombination with increasing temperature; this was consistent with the temperature-related behavior of the emission energy. In addition, the temperature dependence of the intensity ratio of PM to PD further shows that the enhanced thermalization effect of the carriers inside the QDs with increasing temperature, resulted in the significant decrease of PD intensity relative to PM intensity.