Nano structure films of cadmium thiogallate CdGa2S4 have been prepared by a conventional thermal evaporation technique (at substrate temperature = 303 K). These films
were deposited on both glass and quartz substrates. X-ray diffraction
measurements showed that CdGa2S4 compound in the powder form has a
polycrystalline nature with a tetragonal structure. The as-deposited film
was annealed at 673 K for 2 h under vacuum 10-3 Pa and was irradiated
by 10 kGy γco rays. This resulted in a transformation to
nanostructure grains of CdGa2S4 thin films. Transmission electron
microscopy was carried out for all of the investigated films, which also
confirmed that those films could be transformed to nanostructure grains.
Optical properties of the CdGa2S4 films under investigation were
examined using spectrophotometric measurements of transmittance and
reflectance at normal incidence in the wavelength range 400–2500 nm. It was
found that both refractive index n and absorption index k changed with the
heat and irradiation treatments. The dispersion of refractive index in
CdGa2S4 was analyzed according to the single oscillator model.
Some dispersion parameters were determined for all investigated films. The
calculated values of β (which is defined as the parameter used to
determine the type of crystal) indicate that CdGa2S4 belongs to
the covalent class for all films investigated. The ratio of the free carrier
concentration to the effective mass N/m* was also determined.
The analysis of the absorption coefficient indicated that this ternary
defect chalcopyrite compound has both direct and indirect transitions in relevance to the energy gaps Eg1dir, Eg2dir and Egind, respectively. These energy values decreased by irradiation, while they increased by annealing.