Optical properties of nitride quantum wells: How to separate fluctuations and polarization field effects

Both the large linewidth of optical transitions as well as the sizeable "St okes'' shift seem to suggest strong localization effects in nitride quantum wells. In contrast, we clearly show that the "Stokes" shift can be easily understood in terms of the huge piezoelectric fields present in such struct ures. At the same time, those fields lead to a characteristic dependence of the linewidth on well width, which we use to quantitatively separate fluct uation and field effects. We find that in high-quality quantum wells, the r elative compositional fluctuation is less than 10% and the well width fluct uation is of the order 1 monolayer.