TEMPERATURE-DEPENDENCE OF THE OPTICAL-ABSORPTION EDGE IN AMORPHOUS CD-AS AND ZN-P THIN-FILMS

Temperature dependencies of the optical absorption edge in the amorpho us Cd29As71 and Zn32P68 films have been obtained from transmission mea surements in the 5-300 K temperature range. The absorption edges for t hese films were found to follow the Tauc power law with the optical ps eudogap E-G significant increase with decreasing temperature. A nearly linear dependence of E-G on temperature was found in the range from 1 00 It to about 300 K, while below 100 K the energy gap is almost indep endent of temperature. For the Cd29As71 film E-G was found to be equal to 0.76 eV at 5 K and 0,63 eV at 300 K, while for Zn32P68 film, the e nergy gap changes from 1.46 to 1.27 eV in the same temperature range, In contrast to E-G, the Urbach energy decreases rather slightly with d ecreasing temperature. The observed change of the optical gap may be a ttributed to an increase of the mobility gap due to contraction of int eratomic distances with decreasing temperature. (C) 1997 Elsevier Scie nce S.A.