Infrared spectra of GaxIn1−xSe

Abstract

Single crystals of GaxIn1−xSe have been grown in our laboratory by the Bridgman method for x ≤ 0.20 and x ≥ 0.75. Reflectivity measurements in the far infrared, with [Formula: see text], have shown that these alloys have a two-mode behaviour except for x = 0.982 where only the GaSe-like oscillator is visible. A Kramers–Kronig analysis enabled us to obtain a first evaluation of the transverse optic (TO) and longitudinal optic (LO) frequencies of the observed modes. Aχ2 fit of the reflectivity calculated from the factorized model of the dielectric constant produced a more accurate determination for these frequencies along with their respective damping constants and ε0 and εx. Reflectivity measurements for [Formula: see text] were made on indium-rich samples, but only in InSe were the results different from those for[Formula: see text]. These are interpreted as a contamination of the [Formula: see text] mode by the E′ modes, normally visible with [Formula: see text] A model proposed by Jahne for the behaviour of optical phonons in alloy systems is applied to this study and finally a review of the criteria for the one-mode and two-mode behaviour, applied to the GaxIn1−x Se system, is given.