OPTICAL INVESTIGATIONS ON INXSE1-X THIN-FILMS .3. EFFECT OF COMPOSITION

The long-wavelength tail of the optical absorption in five InxSe1-x fi lms (0.05 less than or equal to x less than or equal to 0.25 at.), ann ealed at different temperatures (for a fixed time 2 h), in the spectra l range 1.1-3.9 eV at room temperature is shown to obey Urbach's rule. The measurements indicate that the absorption mechanism is due to all owed indirect and forbidden direct transitions. The dependence of the optical gap E(g)(opt), high-frequency dielectric constant epsilon'(inf inity) and the ratio of the carrier concentration to the effective mas s N/m on the annealing temperature as well as on the In content is re ported and discussed. A semiempirical relationship giving the practica l possibility to synthesize a sample with a predetermined energy gap w ithin the boundary values is made. The structure analysis of the films by using XRD is reported.