Raman spectra of the chalcopyrite compound CuGaTe2

Raman spectra of the chalcopyrite compound CuGaTe2 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 frequ ency phonon mode at 272 cm(-1) is attributed to a combination of E and B2 m odes. It is suggested that the: line at 117 cm(-1) is due to the chalcopyri te-forbidden A(2) mode activated by structural disorder. A broad, but weak, band observed between 80 and 110 cm(-1) is tentatively attributed to scatt ering, due to free holes or collective excitations. A shift to higher frequ ency 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 expa nsion coefficient of chalcopyrites at low temperatures. The temperature var iation of the full width at half maximum (FWHM) of the A(1) mode could be e xplained by considering the decay of the Raman phonon in a combination of t wo phonons, in addition to the contribution, at low temperatures, of a ther mal expansion term. (C) 2001 Elsevier Science Ltd. All rights reserved.