MICROPROBE RAMAN-STUDY OF THE VARIATION OF LO PHONON FREQUENCY WITH THE CD CONCENTRATION IN THE TERNARY COMPOUND ZN1-XCDXSE

Experimental and theoretical studies of II-VI and III-V ternary alloys suggest that the long wavelength optical phonons exhibit one of two t ypes 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 mod ified version of this model we have predicted that ZnCdSe will be of s ingle mode type, and have calculated LO phonon frequency shifts with c omposition. Room temperature microprobe Raman measurements on samples of MBE grown Zn1-xCdxSe with x ranging from 0 to 0.35 show a linear va riation of a single LO phonon peak with composition, confirming our pr edictions, with good agreement with theory for low mole fraction of ca dmium.