Optical properties of AgBiSe2 thin films

Thin films of AgBiSe2 were prepared by thermal evaporation in vacuum (10(-6) Torr). The effect of thermal annealing either in vacuum or in a selenium atmosphere on the growth characteristics and stability of the films were studied using X-ray diffraction, transmission electron microscopy and the selected area electron diffraction techniques. It was observed that the as-deposited films (300 K) were poor crystalline. The degree of crystallinity increases with increasing the temperature From 300 to 473 K. Al 500 K in vacuum two-phase films with AgBiSe, as the major phase were formed. The optical constants of crystalline AgBiSe2 thin films were estimated as well as the effect of heal treatments and selenium vapor pressure on these constants. The analysis of the optical absorption spectra revealed the existence of two optical transition mechanisms: allowed direct and indirect transition, with optical energy gaps E(g)(d) = 1.66 eV and E(g)(i) = 0.91. eV at 300 K. These values were found to decrease with increasing annealing temperature.