Optical properties of ordered In0.5Ga0.5P alloys

Abstract

We study the structural stability and the optical properties of ordered In0.5Ga0.5P alloys in the CuPt-, CuAu-I-, and Y2-type structures through first-principles pseudopotential calculations. The Y2-type structure is found to be stabilized against phase segregation into binary constituents at T=0 when epitaxially grown, with the smaller formation enthalpy than for the CuPt- and CuAu-I-type phases. The CuPt- and Y2-type structures show an asymmetry feature in epsilon(2)(omega) for two perpendicular polarizations along the [110] and [1(1) over bar0$] directions. We find that in the CuPt-type structure the zone folding effect of the L point into the center of the Brillouin zone leads to the enhancement of epsilon(2)(omega), giving rise to an anomalous peak at 2.35 eV in electroreflectance spectra, while the lower energy peak observed at 2.2 eV is caused by the folded-X point in the Y2-type structure.