Structural characterization and novel optical properties of defect chalcopyrite ZnGa₂Te₄ thin films

Stoichiometric thin film samples of the ternary ZnGa₂Te ₄ defect chalcopyrite compound were prepared and characterized by X-ray diffraction technique. The elemental chemical composition of the prepared bulk material as well as of the as-deposited film was determined by energy-dispersive X-ray spectrometry. ZnGa₂Te₄ thin films were deposited, by conventional thermal evaporation technique onto highly cleaned glass substrates. The X-ray and electron diffraction studies revealed that the as-deposited and the annealed ZnGa₂Te₄ films at annealing temperature t_a ≤ 548 K are amorphous, while those annealed at t_a ≥ 573 K (for 1 h), are polycrystalline. The optical properties of the as-deposited films have been investigated for the first time at normal incidence in the spectral range from 500 to 2500 nm. The refractive index dispersion in the transmission and low absorption region is adequately described by the Wemple-DiDomenico single oscillator model, whereby, the values of the oscillator parameters have been calculated. The analysis of the optical absorption coefficient revealed an in-direct optical transition with energy of 1.33 eV for the as-deposited sample. This work suggested that ZnGa ₂Te₄ is a good candidate in solar cell devices as an absorbing layer.