OPTICAL-PROPERTIES OF AMORPHOUS AND POLYCRYSTALLINE STIBNITE (SB2S3) FILMS

A systematic optical absorption study near the fundamental absorption edge was carried out on both amorphous and polycrystalline films of Stibnite in the temperature range 90-320 K. Films were grown using naturally occurring single crystals of Stibnite. The optical band gap of thermally evaporated films which have the stoichiometry Sb43S57 was determined to be direct and temperature dependant. The band gap of amorphous phase at any temperature is considerably less than that of crystalline ones. The temperature dependence of band gap in both the cases agrees well with Varshni formula. The optical gap at 0 K for amorphous and crystalline films were determined by fitting experimental data to Varshni formula to be 1.95 eV and 2.13 eV with the temperature coefficient of band gap -8.72x10(-4) eV/K and -7x10(-4) eV/K respectively. We strongly believe that the band gap value depends on the sulphur content in the films. The films of thickness greater than 2000 Angstrom show interference pattern in the transmission spectra. The optical constants n and k were determined using the interference fringes in the wavelength range 600 - 900 nm for film thickness 2000 - 8000 Angstrom. In both cases n and k show thickness dependence.