ISSN 1063-7826, Semiconductors, 2013, Vol. 47, No. 6, pp. 761–766. © Pleiades Publishing, Ltd., 2013. Original Russian Text © T.G. Kerimova, N.A. Abdullaev, I.A. Mamedova, Z.I. Badalova, R.A. Guliev, R. Raucar, K. Wakita, N.T. Mamedov, 2013, published in Fizika i Tekhnika Poluprovodnikov, 2013, Vol. 47, No. 6, pp. 751–756. 761 1. INTRODUCTION compounds (A—Zn, Cd; B—In, Ga; C—S, Se, Te), which crystallize in the space group , attract the attention of researchers in connection with the possibility of their use in semiconductor devices fabrication. Birefringence, a significant coeffi- cient of nonlinear receptivity, high sensitivity, and bright photoluminescence are characteristic of these compounds. Both experimental and theoretical stud- ies of electron and phonon states occupy a special place. On the one hand, knowledge of the phonon spectra, their dependence on temperature, pressure, and other external factors are important when inter- preting the mechanisms of heat capacity and heat con- duction in semiconductor compounds. Joint theoreti- cal and experimental studies of the phonon spectra make it possible to acquire information on phonon frequencies, the force constants of interatomic bonds, the phonon–phonon and phonon–electron interac- tion, etc. On the other hand, studying alloys of semiconduc- tor compounds is a topical problem. A gradual varia- tion in many parameters (the band-gap width, the effective mass of carriers, photoconductivity, photolu- minescence, etc.) forms the possibility for their use as tunable optoelectronic converters. A II B 2 III C 4 VI S 4 2 We previously studied the infrared reflection and Raman scattering spectra in CdGa 2 Se 4 and CdGa 2 S 4 [1–3]. The observed optical phonons are identified by their symmetry types. Optical phonons are also stud- ied by Raman spectroscopy in [4–8]. There is good agreement upon identifying phonons by their symme- try types. The authors of [9] studied the Raman spectra of CdGa 2 S 4x Se 4(1 – x) alloys. To identify optical phonons, a sphalerite-like model is used. In this study, we represent the results of investiga- tion of the Raman spectra for CdGa 2 S 4x Se 4(1 – x) alloys with the purpose of establishing correspondence between the frequencies of optical phonons and atomic displacements in the unit cell. 2. OBTAINING THE CdGa 2 S 4x Se 4(1 – x) SINGLE CRYSTALS AND THE EXPERIMENTAL PROCEDURE The single crystals of CdGa 2 S 4x Se 4(1 – x) alloys were grown by the method of gas-transport reactions. As the transport substance, we used crystalline I. We per- formed X-ray diffraction studies and determined the lattice parameters; the space group is . Parameter a is almost invariable upon the substitution of Se with S, while parameter c decreases and a nonlinear depen- dence is observed at x = 0.4–0.6, i.e., the Vegard rule S 4 2 Optical Phonons in CdGa 2 S 4x Se 4(1 – x) Alloys T. G. Kerimova a ^, N. A. Abdullaev a , I. A. Mamedova a , Z. I. Badalova a , R. A. Guliev a , R. Raucar b , K. Wakita b , and N. T. Mamedov a a Institute of Physics, National Academy of Sciences of Azerbaijan, pr. Dzhavida 33, Baku, AZ-1143 Azerbaijan ^e-mail: rair-kerimova@mail.ru b Chiba Institute of Technology, 275-0016 Narashino, Chiba, Japan Submitted July 23, 2012; accepted to publication August 13, 2012 Abstract—The Raman spectra of CdGa 2 S 4x Se 4(1 – x) alloys (x = 0.1, 0.2, … 0.9) are studied. Both the single- mode and double-mode behavior of optical phonons are observed in CdGa 2 S 4x Se 4(1 – x) alloys. The observed optical mode at 138 cm –1 is independent of the composition. It seems likely that this mode is the “breathing mode” and is caused by atomic motion in the anion sublattice relative to vacancies. It is shown that the high- frequency modes of symmetry B 1 (LO, TO) and B 2 (LO, TO) are caused by the in-phase motion of atoms in the anion sublattice along the tetragonal axis c relative to trivalent Ga atoms. The doubly degenerate symme- try modes E 1 (LO, TO) and E 2 (LO, TO) are caused by the in-phase motion of atoms in the anion sublattice relative to trivalent Ga atoms of the cation sublattice in the xy plane (dipole 2Ga–4C), where C is S, Se. The optical symmetry modes B 3 (LO, TO) and B 4 (LO, TO) are associated with the motion of atoms in the anion sublattice relative to Cd atoms along the tetragonal axis c. The doubly degenerate modes E 3 (LO, TO) and E 4 (LO, TO) are associated with the motion of atoms in the anion sublattice relative to Cd atoms (dipole Cd 4C). The low-frequency modes B 5 (LO, TO) and E 5 (LO, TO) are the analogs of acoustic phonons at the edge of the Brillouin zone of sphalerite. DOI: 10.1134/S1063782613060110 SPECTROSCOPY, INTERACTION WITH RADIATION