Phonon Assignments in ZnSe and GaSb and Some Regularities in the Phonon Frequencies of Zincblende-Type Semiconductors

Abstract

The lattice infrared-absorption spectra of ZnSe and GaSb reported in the literature are analyzed to obtain the values of the optical and the acoustical phonon energies at or near the Brillouin zone boundary. For ZnSe, which has an effective ionic charge of 0.7, the LO and TO phonons are found to have about the same energy near the zone boundary as anticipated by Keyes for compounds of intermediate ionicity. Mass ratio and effective ionic-charge effects in the critical-point phonon energies of the zincblende-type semiconductors are investigated with the presently available data. The difference in the values of the longitudinal and the transverse optical modes at the zone center is found to be a linear function of ionicity. If the observed infrared spectra of these compounds are analyzed on a four-phonon scheme, new correlations are obtained between the optical and the acoustical phonon energies. These correlations are discussed in terms of dispersion relations.