Effect of heat treatment on some of the optical parameters of Cu9Ge11Te80 films

Some optical parameters of as-deposited and annealed Cu9Ge11Te80 films were studied in the visible spectral range using both absorbance and transmittance measurements. The absorption coefficient was computed and the analysis of the data revealed the existence of two optical transition mechanisms. The direct optical energy gap E-gd decreases from 1.74 to 1.58 eV as the film annealed to 520K. Such behavior is attributed at present to unsaturated defects, which increase the density of localized states. The width of the tails of localized states E-c were calculated and found to be increased at high annealing temperatures. Films annealed at high temperature (T-a > 420 K) show a splitting of valence band by the spin orbit interaction. One may conclude that at high concentrations of Cu (x = 9), it is likely that the glass forming ability decreases. Other optical parameters (epsilon(i), epsilon(r), n and k) were calculated at different annealing temperatures. (C) 2002 Published by Elsevier Science, Ltd.