Exciton hopping in InxGa1-xN multiple quantum wells -: art. no. 085306

The dynamics of photoexcited excitons in thin InGaN/GaN multiple quantum wells (QW's) with different In contents was studied by comparing the experimental data obtained by photoluminescence (PL), PL excitation, and photoreflectance spectroscopy techniques with the results of Monte Carlo simulations of exciton hopping. The temperature dependence of the PL linewidth was demonstrated to be in a fair agreement with the model of phonon-assisted exciton in-plane hopping within In-rich regions with inhomogeneous broadening taken into account. The band potential fluctuations, which scale the dispersion of localized states the excitons are hopping over, were attributed to compositional disorder inside the In-rich regions. Meanwhile, the inhomogeneous broadening was explained by variation in mean exciton energy among the individual In-rich regions. For typical 2.5-nm-thick InxGa1-xN (x approximate to 0.22) QW's, the simulation revealed fluctuations of the band potential (31 meV) with additional inhomogeneous broadening (29 meV) and a crossover from a nonthermalized to thermalized exciton energy distribution at about 150 K. Both the fluctuations and inhomogeneous broadening showed an enhancement with increasing of In content. Simultaneously, a Bose-Einstein-like temperature dependence of the exciton energy in the wells was extracted using data on the PL peak position. The dependence exhibited a fair conformity with the photoreflectance data. Moreover, the density of localized states used in the simulation was found to be consistent with the PL excitation spectrum.