<title>Time-resolved photoluminescence studies of GaN, InGaN, and AlGaN grown by metalorganic chemical vapor deposition</title>

Abstract

Time-resolved photoluminescence (PL) measurements are reported for GaN, InGaN, and AlGaN thin films, as well as InGaN/GaN multiple quantum wells (MQWs) with 3-nm-thick InGaN wells and 4.5-nm-thick GaN barriers. All the samples were grown on c-plane sapphire substrates by metalorganic chemical vapor deposition. We observed that the carrier recombination lifetime of the ternary InGaN and AlGaN alloys becomes longer with decreasing emission energy. An anomalous temperature-dependent emission behavior was observed for InGaN-related PL with increasing temperature. The actual temperature dependence of the PL emission was estimated with respect to the bandgap energy determined by photoreflectance spectra. The temperature-induced S-shaped PL shift is explained by a change in the carrier dynamics with increasing temperature due to inhomogeneity and carrier localization in the alloys. We also investigated the influence of Si doping on the optical characteristics of InGaN/GaN MQWs. The 10 K radiative recombination lifetime was observed to decrease from approximately 30 ns to approximately 4 ns with increasing Si doping concentration from &lt; 1 X 10<SUP>17</SUP> to 3 X 10<SUP>19</SUP> cm<SUP>-3</SUP>. A reduced Stokes shift between PL and PL excitation spectra, a reduction in a pump-density-induced blueshift, and an increase in the interface quality with increasing Si doping were observed. From these results, we conclude that Si doping results in a decrease in carrier localization caused by potential fluctuations in the MQWs.