FIZIKA A 5 (1996) 4, 177-184

OPTICAL PROPERTIES OF AgBiS₂ THIN FILMS

ALAA M. IBRAHIM and LAILA I. SOLIMAN^a
University College for Girls, Ain Shams University, Physics Dept., Heliopolis, Cairo, Egypt
^aNational Research Centre, Physics Department, Dokki, Cairo, Egypt

Received 20 August 1996

Thin films of AgBiS₂ were prepared by thermal evaporation in vacuum (at about 10^-6 mbar). X-ray diffraction was used to determine the structural properties of the sample. The as-deposited films (at 300 K) were amorphous in nature and an amorphous-to-crystalline transition could be obtained by thermal annealing at 373 K. The degree of crystallinity increased with increasing temperature from 373 to 473 K. At 525 K, two-phase films with AgBiS₂ as a major phase were formed. Optical constants of amorphous and crystalline AgBiS₂ thin films were measured after various heat treatments. The analysis of optical absorption spectra revealed the existence of three optical transition mechanisms; allowed direct, forbidden direct and indirect transition, with optical energy gaps E_d = 2.88 eV, E_f = 2.04 eV and E_i = 1.78 eV at 300 K. These values were found to decrease at higher annealing temperatures.

UDC 538.958
PACS 78.66.-w

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