Impact of film thickness on optical properties and optoelectrical parameters of novel CuGaGeSe₄ thin films synthesized by electron beam deposition

The authors in this article present the synthesis of good quality CuGaGeSe₄ thin films of different thicknesses using electron beam deposition on well pre-cleaned glass substrates. X-ray diffraction patterns displayed the amorphous nature of as-prepared CuGaGeSe₄ thin films. In addition, the elemental compositional analysis of these films was examined by the energy-dispersive X-ray spectroscopy technique, which showed that there is good matching between the selected and detected percentages. Transmittance and reflectance spectra of these CuGaGeSe₄ samples were measured to experimentally determine the absorption coefficient and some related optical parameters. Optical band-gap energy values of samples were determined via Tauc’s Plots; they are arisen owing to the indirect allowed transition. They are decreased from 1.43 to 1.29 eV by increasing the film thickness from 250 to 445 nm. The skin depth, absorption index, and refractive index of CuGaGeSe₄ thin films were also obtained and extensively studied. As well as, some optoelectrical parameters of these investigated films were discussed, like optical resistivity, optical mobility, optical conductivity, the lattice dielectric constant, and the ratio of the charge carrier concentrations to the effective mass (N_opt/m*). Along with, some nonlinear optical parameters of CuGaGeSe₄ films were studied employing Miller’s formulas. The values of the dispersion energy, static refractive index, the static dielectric constant, the oscillator strength and others increase, while the oscillator energy and the relaxation time decrease as the film thickness increased. The obtained results showed that these CuGaGeSe₄ film samples can be successfully used as absorption layers in thin-film solar cells.