Local structural distortions in InAsP/InP strained layer superlattices

The local structure around As in thin InAsxP1-x strained layers in InAsxP1-x/InP superlattices has been probed by fluorescence detected XAFS as a function of composition, and compared to that found in unstrained, bulk samples of similar composition. Contributions up to the third coordination shell around As were clearly visible in the spectra and were analyzed taking into account the major multiple scattering contributions. Differences in the local structure between the thin strained films and the bulk alloys are expected to arise from tetragonal strain due to epitaxy with the substrate. Results are consistent with a picture in which long range order in the strained layers is mainly achieved via bond angle distortions, as first shell bond distances follow the measured and theoretically predicted values of the bulk alloys. Evidence of the influence of tetragonal distortion on the local structure appears in further coordination shells.