Effects of localization on the excitonic linewidth in partially orderedGaxIn1−xPalloys

Abstract

Spontaneous ordering in the ternary alloy GaxIn1−xP naturally leads to a reduction in alloy scattering and thus a reduction in the excitonic linewidth with increasing order parameter h. Concomitantly, the effect of localized states associated with various defects tends to increase the exciton linewidth, and it was observed that for hu0.45, the linewidth actually increases with order parameter [Phys. Rev. B 61, 9910 (2000)]. This was attributed to the increase in native defects which occurs for higher order parameters due to limitations in current growth technology. We show, using spatially resolved PL imaging with confocal and near-field microscopy, that this trend is reproduced in all orderedGaxIn1−xP samples, within the micro-ensemble formed by the collection of all spectra in a spatially and spectrally resolved PL image, directly imaging the effect of exciton localization. This reversed trend is a result of the interplay between the effects of localization and spontaneous ordering, and the spatial averaging which occurs when examining areas many times larger than the exciton Bohr radius. Agreement with the trend observed in macro-PL is obtained via micro-ensemble averaging of each data set, and by examination of the spatial correlation of exciton linewidths. The implications of these results on the origin of the exciton linewidth in ordered alloys and the effect of ordering on the spatial distribution of exciton linewidths are discussed.