Optical characteristics of InGaN/GaN quantum well structures with embedded quantum dots

We compared the results of optical characterization between five InGaN/GaN quantum well samples of different well widths. Temperature dependencies of photoluminescence (PL) spectral positions, integrated PL intensities, and PL intensity decay times at PL peaks of all the five samples showed three temperature ranges of different variation trends. The radiative efficiencies of the samples in the high temperature range had the same decay slope, which is supposed to be determined by the defect structures outside clusters. The radiative efficiencies in the medium temperature range varied among samples, indicating different defect structures in the regions between coupled clusters in different samples. Consistent results of temperature dependent variations between the integrated PL intensity and PL decay time among these samples provided clues for reasonable interpretations. Also, we showed the strong dependencies of thermal annealing effects on quantum well (QW) width in InGaN/GaN QW structures. Thermal annealing at 800 °C of a narrow QW width (2 nm) structure led to improved optical quality. However, thermal annealing at the same temperature of a sample of larger QW width (4 nm) resulted in degraded optical quality.