Spatially resolved below-gap emission in partially orderedGaxIn1−xPalloys

We have examined the spatial variation in the photoluminescence (PL) of a series of partially ordered ${\mathrm{Ga}}_x{\mathrm{In}}_{1-x}\mathrm{P}$ $\mathrm{}(x=0.52\mathrm{})\mathrm{}$ samples with order parameters ranging from $\eta \sim 0.12$ to $\eta \sim 0.49$ using low-temperature scanning confocal, scanning solid immersion lens, and scanning and fixed-aperture near-field microscopy with spatial resolution in the range from 200 nm to $0.7\mu \mathrm{m}$. A wide variation in the characteristic low-energy emission band and the associated ultrasharp PL lines was observed for samples with similar ordering-related properties (e.g., $\eta$ and domain size). In particular, not all samples exhibit sharp-line PL when examined using $\mu$-PL techniques. In samples that do show these lines, near-field spectroscopic imaging is used to map their location in space with respect to the more slowly varying excitonic emission: no spatial correlation between the antiphase boundaries (APB’s) which form in these alloys and the appearance of ultrasharp PL lines was observed. A correlation between the occurrence of ultrasharp PL lines and the presence of extended defects was found for some samples. Temperature-dependent and time-resolved studies show evidence of excitation transfer between a dense ensemble of discrete, localized states. The data suggest that models appealing solely to the properties of the APB in ordered GaInP cannot explain this emission, and that extended defects and/or impurities may play a more important role than previously thought.