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

Abstract

We study the structural stability and the optical properties of ordered ${\mathrm{In}}_{0.5}$${\mathrm{Ga}}_{0.5}$P 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 ${\ensuremath{\epsilon}}_{2}(\ensuremath{\omega})$ for two perpendicular polarizations along the [110] and [$1\overline{1}0$] 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 ${\ensuremath{\epsilon}}_{2}(\ensuremath{\omega})$, 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.