Optical Absorption and Structural Properties of as-deposited and Thermally Annealed As-Te-Ga Thin Films

Thin films of As30 Te70-x Gax, where x = 0.5, 1, 3, 6 and 10 are deposited
on glass substrates by vacuum evaporation. The transmittance and absorbance
of the as-deposited films were measured in the spectral range 400-1100nm. The
dependence of the absorption coefficient on the photon energy is well described
by the relation αhν= B (hν-E0)2. The optical energy is nearly independent on the
Ga content up to 3 at.% , then increases continuously from 0.73 eV to 0.9eV
with increasing the Ga content. Thermal annealing below and above the glass
transition temperature slightly increase and decrease the value of the optical
energy gap, respectively. XRD, SAED, TEM and DSC were used to study the
structure of the as-deposited and annealed films. The amount and type of the
separated polycrystalline phases depend on the original composition of the film
and on the annealing temperature.