STRUCTURAL AND OPTICAL-PROPERTIES OF CDGA2SE4 THIN-FILMS

CdGa2Se4 thin films were prepared by vapour deposition onto either roo m temperature or preheated quartz and glass substrates (T(S)) or they were deposited at room temperature and then annealed at about (T(A)) 6 23 K. The films thus prepared were crystalline with a thiogallate tetr agonal structure. The optical constants (the refractive index n and th e absorption index, k) were determined for CdGa2Se4 films deposited on to quartz substrates held at either room temperature or at T(S) = 573 K. These constants were also determined for preannealed films (T(A) = 623 K). Plots of (alphahnu)2 = f(hnu) and (alphahnu)1/2 = g(hnu) were linear, indicating the existence of both direct and indirect optical t ransitions. It was found that the values of E(g)d and E(g)ind for as-d eposited CdGa2Se4 films were 2.46 and 1.91 eV, respectively. The corre sponding values for the annealed films and the films deposited at T(S) = 573 K were 2.56 and 2.06 eV, respectively.