Band-gap reduction and valence band splitting in spontaneously ordered GaInP₂ studied by dark-field spectroscopy

Transmission dark-field spectra (DFS), i.e. the transmittivity of a sample positioned between crossed linear polarizers, are measured in the energy range (1.65 - 1.9)eV on partially ordered GaInP layers grown on (001)-GaAs. Different degrees of order were expected in GaInP due to the reported growth conditions. Using the generalized light polarization transfer matrix technique [D. W. Berreman, J. Opt. Soc. Am. 62 (1972) 502] the ordering induced band-gap reduction (BGR) and valence band splitting (VBS) inside the ordered domains were deduced from the DFS. Applying theoretical considerations recently predicted by Wei et al. the order parameters for each sample were determined. The ordered domains are found to be uniaxial whereas disordered GaInP is cubic and therefore isotropic. The results for the BGR and VBS energies are obtained macroscopically and regardless of the volume fraction and the size of the ordered microscopic domains.