Raman spectra of the chalcopyrite compound CuGaTe2

Abstract Raman spectra of the chalcopyrite compound CuGaTe 2 were obtained between 80 and 300 K. Lines observed at 54, 76, 155, 170, 211 and 220 cm −1 , and at 70, 204 and 224 cm −1 were assigned to E and B 2 modes, respectively. The most intense line at 135 cm −1 , and others at 64, 148, and 190 cm −1 , are assigned to A 1 mode and to B 1 symmetry, respectively. The highest-frequency phonon mode at 272 cm −1 is attributed to a combination of E and B 2 modes. It is suggested that the line at 117 cm −1 is due to the chalcopyrite-forbidden A 2 mode activated by structural disorder. A broad, but weak, band observed between 80 and 110 cm −1 is tentatively attributed to scattering, due to free holes or collective excitations. A shift to higher frequency with increasing temperature, of A 1 , B 2 and E modes below 120 K, is explained due to the contribution of the negative value of the thermal expansion coefficient of chalcopyrites at low temperatures. The temperature variation of the full width at half maximum (FWHM) of the A 1 mode could be explained by considering the decay of the Raman phonon in a combination of two phonons, in addition to the contribution, at low temperatures, of a thermal expansion term.