Growth, Structural Characterization, and Optical Band Gap Anomaly in Cu-III3-VI5 and Cu-III5-VI8 Ternary Compounds

Abstract

ABSTRACTA comparative study of the chemical composition, crystal structure, carrier concentration, mobility, and the energy gap at room temperature of the selenides and tellurides of normal Cu- III-VI2 and ordered defect Cu-III3-VI5and Cu-III5-VI8 compounds, grown by Bridgman techniques, is made. It is established that these compounds have a chalcopyrite-related structure with the exception of CuIn5Se8 and CuGa5Te8 that have hexagonal and cubic structure, respectively. Smaller volume of the unit cell and lower concentration of the charge carrier of the 1:3:5 and 1:5:8 phases, as compared to the 1:1:2, are attributed to the presence of the ordered vacancies. A new mechanism of the scattering of the charge carriers with the donor-acceptor defect pair (DADP) is suggested to explain the low value of mobility in these compounds. The anomaly observed in the band gap is explained in terms of the relative shift of the conduction band minimum and valence band maximum due to the donor-acceptor defect pairs and cation vacancies, respectively.