Phonon Structures in Optical Spectra of Layer Compounds GaSe and GaS

概要

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The infrared and far-infrared absorption spectra of β-GaSe and GaS have been measured in the temperature range from 50 to 300°K for the radiation polarized perpendicular to the c-axis in the hexagonal layer structure of these compounds. The reststrahlen frequencies measured at room temperature are 211.0 cm^<-1> in β-GaSe and about 310 cm^<-1> in GaS, respectively. In addition, the weak absorptions in the wave number range from 400 cm^<-1> to 750 cm^<-1> are identified with the multiphonon absorptions in the light of group theoretical analysis and of the experimental results on the Raman effect and on the electro-luminescence available up to date. The absorption line at 512 cm^<-1> and band around 450 cm^<-1> in β-GaSe are explained in terms of the localized mode of lattice vibrations induced possibly by an oxygen impurity. This analysis is the first preliminary investigation on the localized mode in a diatomic crystal of hexagonal structure.
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