The effect of thickness and heat treatment on the structural and optical
properties of Sb2Te3 thin films fabricated by using flash
evaporation technique were investigated. The as-deposited films were found
to be stoichiometric. For the as-deposited and annealed samples of thickness
in the range of 20.7–120.5 nm, large variations in transmittance and
reflectance were observed for wavelength below 2000 nm due to strong
absorption, while slight variations were observed above 2000 nm. The optical
constants, n and k, measured in the range of 500–4000 nm, increased slightly
by annealing the samples at 573 K for 2 h in air and a red shift was
observed. Allowed indirect transitions were observed for the as-deposited
and the annealed samples. The results showed two energy gaps for these
transitions varied from 0.28 to 0.31 eV for the as-deposited samples and
from 0.56 to 0.54 eV for the annealed films. The spectral distribution of
the real part of the dielectric constant ε′ showed a maximum at
0.73 eV for the as-deposited films decreased to 0.65 eV by annealing.