Carrier localization in strong phase-separated InGaN/GaN multiple-quantum-well dual-wavelength LEDs

Dual-wavelength light-emitting diodes (LEDs) based on InGaN/GaN multiple quantum wells (MQWs) were grown by metal organic chemical vapor deposition. The strong phase separation in the InGaN layer led to high-density, indium-rich quasi-quantum dots (QDs) in the InGaN/GaN MQWs. The photoluminescence (PL) spectra consisted of green and blue emissions around 2.37 and 2.71 eV, which originated from the quasi-QDs and InGaN matrix, respectively. The effect of carrier localization on the two emissions was explored using a combination of energy-dependent time-resolved PL, temperature-dependent PL, and excitation-dependent PL measurements. Experimental results indicated the co-existence of shallow and deep localized states in the sample: the shallow localized states originated from the InGaN matrix, and the deep localized states originated from the phase-separated quasi-QDs. The green emission from the deep localized quasi-QDs showed a higher luminescence intensity and higher thermal stability than the blue emission from the shallow localized InGaN matrix. These results can be explained by our proposed model, which provides a considerable insight into the carrier localization and luminescence mechanism in strong phase-separated InGaN/GaN MQW dual-wavelength LEDs.