Effects of barrier growth temperature ramp-up time on the photoluminescence of InGaN/GaN quantum wells

The influence of ramp-up time of barrier growth temperature on optical properties is investigated for InGaN/GaN quantum wells deposited on sapphire substrate by metal organic chemical vapor deposition. Three ramp-up times are used from the low and high growth temperatures for the well and barrier, respectively. The results indicate that increasing the ramp-up time leads to a blueshift of the photoluminescence (PL) peak position and a broadening of the PL emission linewidth. Similarly, “S-shaped” temperature dependences of the PL peak energy are observed in all the samples. However, very different temperature dependences of PL linewidth, such as the conventional shaped, “U-shaped,” and S-shaped, are observed in the samples with different ramp-up time. These effects are attributed to the redistribution of the In-rich clusters in the wells. Small quantum-dot-like In-rich clusters with high density are considered to be formed in the wells for the sample with a long ramp-up time, leading to the unconventional PL linewidth behavior and enhanced internal quantum efficiency.