Hs. Soliman et al., OPTICAL-PROPERTIES OF THERMALLY VACUUM-EVAPORATED AGSBSE2 THIN-FILMS, Journal of physics. Condensed matter, 10(4), 1998, pp. 847-856
Silver antimony diselenide (AgSbSe2) thin films were prepared by a the
rmal vacuum evaporation technique onto quartz and glass substrates kep
t at room temperature (similar to 300 K). The as-deposited films were
amorphous and transformed to a face centred cubic (FCC) polycrystallin
e nature with the lattice constant a = 5.797+/-0.003 Angstrom on post-
deposition annealing above 423 K for one hour in argon atmosphere. The
optical constants (the refractive index n, and the absorption index k
) of the films were determined for several samples of different thickn
ess (180 nm-270 nm), using spectrophotometric measurements of the tran
smittance T and reflectance R at normal incidence in the spectral rang
e 500-2500 nm. These constants were also determined for preannealed fi
lms, T-A = 423 K (polycrystalline). The obtained values of both n and
k were independent of the film thickness within the above-mentioned th
ickness range. The refractive index data fitted a single-oscillator mo
del with high-frequency dielectric constants increasing from 13 for th
e amorphous films to 15 for the crystalline films. It was found that t
he high-frequency dielectric constant epsilon(infinity) has the same v
alues as the lattice dielectric constant epsilon(L). The analysis of t
he spectral behaviour of the absorption coefficient in the intrinsic a
bsorption region revealed the existence of an indirect allowed optical
transition with energy gap 1.2 eV for amorphous films and 1.03 eV for
the crystalline films, respectively.