Optical constants and associated functions of CdGa2Se4 thin films

Abstract

A polycrystalline stoichiometric sample of the ternary compound CdGa2Se4 was prepared and characterized by x-ray diffraction analysis. Lattice parameters were determined and compared with data in the literature. CdGa2Se4 thin films were prepared by thermal evaporation under vacuum (10−3 Pa). X-ray diffraction analysis of the deposited films revealed that, the as-deposited films were amorphous in nature and an amorphous-to-crystalline phase transition with a preferred orientation along (112) could be obtained by thermal annealing of the as-deposited films at 425 K for 0.5 h.The optical constants of the deposited films were determined in the spectral range 450–2500 nm. A graphical representation of log(α) versus log(1/λ) shows two distinct, linear parts confirming the existence of both direct and indirect optical transitions. The corresponding band gap values were determined. The refractive index dispersion in the transmission and low absorption region is adequately described by the single oscillator model, whereby the values of the oscillator strength, So, oscillator position, λo, dispersion parameter Eo/So and the high-frequency dielectric constant, ε∞ were calculated. The effective number of valence electrons per atom, n0,eff and the static dielectric constant, ε0,eff are deduced via the use of sum rules and are used to interpret the obtained optical data.