Competing exciton localization effects due to disorder and shallow defects in semiconductor alloys

We demonstrate that excitons in semiconductor alloys are subject to competing localization effects due to disorder (random potential fluctuations) and shallow point defects (impurities).The relative importance of these effects varies with alloy chemical composition, impurity activation energy as well as temperature.We evaluate this effect quantitatively for Mg x Zn 1-x O : Al (0 x 0.058) and find that exciton localization at low (2 K) and high (300 K) temperatures is dominated by shallow donor impurities and alloy disorder, respectively.