Reflectance difference spectroscopy of CuPt-type ordered Ga0.5In0.5P/GaAs

We have built a reflectance difference spectroscopy (RDS) system, which measures the difference of the reflectance of light of two orthogonal eigen-polarizations in the visible and ultraviolet spectral range. The instrument can be used for studying anisotropy of thin film and bulk crystals, surface properties of crystalline materials, or monitoring growth mode. We grew several disordered and CuPt-type ordered lattice-matched GaxIn1-xP (x approximate to 0.5) films grown on GaAs substrate. The CuPt-type-ordered GaxIn1-xP (x approximate to 0.5) gave a RDS signal due to the anisotropy in reflectance. The CuPt-type-ordering effect causes a red shift of the E-0 band gap energy. Thus, the E-0 energy changes from as low as 1.78 eV up to 1.92 eV at room temperature. We observed a reduction of the E-0 band-gap energy of Ga0.5In0.5P/GaAs with increasing degree of ordering. We correlated the intensity of the RDS signal near the E-1 gap with the ordering parameter xi, which was estimated from the red shift of the E-0 gap. We found that the RDS signal at the E-1 band gap is closely correlated with the degree of CuPt-type ordering in terms of the peak amplitude as well as the band-gap energy. Our work demonstrates that RDS is a powerful instrument to study anisotropy of thin film crystals.