OPTICAL-PROPERTIES OF TERNARY AGSBS2 THIN-FILMS

Structural and optical properties of amorphous and crystalline ternary AgSbS2 thin films as well as the effect of annealing temperature on t hese properties have been investigated. From the study of x-ray diffra ction patterns, it is clear that the as-deposited films (300 K) are am orphous in nature, whilst those heat treated under vacuum at moderate temperatures (373 K) for 1 h have been transformed from the amorphous structure to a crystalline structure and the crystallinity increases w ith increasing temperature. At 500 K a new crystalline plane, (200), a ppears, characteristic of the binary alpha-AgS2 besides AgSbS2. The op tical constants, absorption coefficient alpha, reflective index n, opt ical energy gap E(g), valence band density of states g(i) and dielectr ic constants epsilon' and epsilon'', were computed for amorphous and c rystalline AgSbS2 films of thickness 169 nm. The analysis of the absor ption coefficient data revealed the existence of two optical transitio n mechanisms, indirect and direct transitions, depending on the value of wavelength range. These energy gaps were found to have the values ( 1.38-1.17 eV) and (2-1.77 eV) in the temperature range from 300 to 473 K for indirect and direct energy gaps respectively.