THE COMPOSITION DEPENDENCE OF THE OPTICAL-CONSTANTS IN AMORPHOUS SBXSE1-X THIN-FILMS

The optical transmission and reflection at normal incidence of amorpho us SbxSe1-x (0 less-than-or-equal-to x less-than-or-equal-to 0.9) thin films of different thicknesses (from 40 to 320 nm) were measured at r oom temperature in the wavelength region 500-1300 nm. From the obtaine d data, the absorption coefficient alpha, the extinction coefficient k , refractive index n, the optical energy gap E(g)opt and the valence b and density of states g(i) were computed for different values of x. Th ese constants were found to be independent of film thickness, but depe nd markedly on the value of the composition x. The analysis of the abs orption coefficient data revealed the existence of two optical transit ion mechanisms, depending on the value of x, indirect transitions for SbxSe1-x thin films (x = 0. 1, 0.4, 0.5, 0.7, and 0.9) and a forbidden direct transition for x = 0.3. The optical energy gap E(g)opt was fou nd to vary from 0.24 eV for (x = 0.9) to 1.92 eV for (x = 0). It was f ound that the high frequency optical constants n and k increase from 3 .7 to 7.4 and from 0.32 to 0.64 respectively with increasing x from 0 to 0.9.