Lattice Vibration Spectra ofGaAsxP1−xSingle Crystals

Abstract

The energies of the two-phonon summation bands and the reststrahlen bands have been measured in $\mathrm{Ga}{\mathrm{As}}_x{\mathrm{P}}_{1-x}$ single crystals. The data were obtained by observing the transmittance and the reflectivity at 300°K in the region of 400 to 800 ${\mathrm{cm}}^{-1\mathrm{}}$ and 220 to 500 ${\mathrm{cm}}^{-1\mathrm{}}$, respectively. Crystals were prepared by open-tube epitaxial vapor-growth techniques and were not subject to any free-carrier absorption in the near infrared. The alloys show absorption peaks at frequencies which are only slightly shifted from the transverse optic $\mathrm{TO}\left(\Gamma \right)$ phonons, as well as several optical and acoustical zone-boundary phonons, characteristic of both GaP and GaAs. The reststrahlen-like band spectra of these alloys are explained by a virtual-crystal model in which average parabolic potentials are given to the three species of atoms in the lattice. This model does not require the assumption of gross composition inhomogeneities, which are known to be absent in these crystals.