Power dependent micro-photoluminescence of green-InGaN/GaN multiple quantum wells

We report the excitation-power-dependent micro-photoluminescence (micro-PL) of green-InGaN/GaN multiple quantum wells grown on a sapphire substrate. By using a micro-PL imaging technique based on laser scanning confocal microscopy, bright luminescent centers emitting blue, green, and yellow bands were clearly resolved at a low excitation power. With increasing power, in addition, the strong blue-shift of PL bands from all luminescent centers was observed, with a much stronger blue-shift for initial yellow band. We show that the band-tail filling model qualitatively agrees well with our microscopic study revealing the origin of apparent bandwidth-narrowing in macroscopic ensemble PL spectra.