Microprobe Raman study of the variation of LO phonon frequency with the Cd concentration in the ternary compound Zn1 − xCdxSe

Abstract

Experimental and theoretical studies of II–VI and III–V ternary alloys suggest that the long wavelength optical phonons exhibit one of two types of behaviour, single or double mode. A semi-empirical model which has had success in predicting LO and TO phonon frequencies for mixed alloys is the random element isodisplacement model (REIM). Using a modified version of this model we have predicted that ZnCdSe will be of single mode type, and have calculated LO phonon frequency shifts with composition. Room temperature microprobe Raman measurements on samples of MBE grown Zn1 − xCdxSe with x ranging from 0 to 0.35 show a linear variation of a single LO phonon peak with composition, confirming our predictions, with good agreement with theory for low mole fraction of cadmium.