Phonon Spectrum of Ternary Alloys

Abstract

Recently measurements on the infrared and Raman scattering spectra of several quaternary alloy systems such as Ga 1 _ xAI xAs 1 _ yP y have been reported. Depending on the concentration, this system can be thought of as either a GaAs-rich quaternary, where GaAs is the host containing the two kinds of impurity Al and P, or as a GaP-rich quaternary, where GaP is the host and Al and As are two impurities. Thus, the properties of such systems can be simulated by a ternary alloy. The coherent potential approximation (CPA) for ternary alloys proposed by Scarfone (1973) is used to analyse the experimental data, assuming a single Einstein oscillator model for the host crystal. The theory, consisting of both diagonal and off-diagonal randomness, agrees well with the observed values, but fails to predict the observed pair modes.