Infrared Lattice Vibrations inGaAsyP1−yAlloys

Abstract

The infrared lattice-vibration spectra of mixed crystals of $\mathrm{Ga}{\mathrm{As}}_{y}{\mathrm{P}}_{1\ensuremath{-}y}$ have been measured by reflection techniques. These crystals exhibit two distinct reststrahlen bands whose strengths and frequencies depend on $y$ and which show considerable fine structure. A harmonic model has been developed to account for the significant features of these spectra. The main features of the model are (1) the inclusion of a clustering effect or nonrandom distribution of anions on a microscopic scale, (2) the existence of 5 distinct molecular complexes which leads to 2 groups of 4 closely spaced optical phonon modes, and (3) effective ionic charges that have both local and nonlocal parts. The model provides the frequencies and strengths of the optical phonon modes which with suitably chosen damping constants yield a good fit to the reflectivity spectrum over the entire range of solid solutions.