ELECTRICAL CHARACTERIZATION OF STABLE AIR-OXIDIZED CDSE FILMS PREPARED BY THERMAL EVAPORATION

Stabilization of the electrical resistivity of CdSe thin films has bee n studied by air oxidation at room temperature (300 K). Depending on t he film thickness, the dark- and photoconductance of the films stabili ze over 12 to 25 days of air exposure. The variation of photosensitivi ty of the films has been explained on the basis of inherent slow recom bination states (k centres) and oxygen-assisted conversion of selenium vacancy, cadmium vacancy, cadmium interstitial (V-Se-V-Cd-Cd-i) to ca dmium vacancy-cadmium interstitial (V-Cd-Cd-i) complexes. The variatio n of oxygen adsorption with film thickness is studied. The temperature variation of dark- and photoconductance measurements in these films r eveals a thermal quenching of photoconductivity at about 265 K. The k centres are located at about 0.23 eV above the top of the valance band . A selenium vacancy-related level is revealed at about 0.12 eV below E(c). This level disappears as a result of long time exposure of the f ilms to atmospheric oxygen. An oxygen-assisted excitonic transition is revealed along with the band edge transition in the spectral distribu tion of photocurrent of oxygen-adsorbed stabilized films.