Combined experimental and DFT-TDDFT computational, structural and study Effect of inter-diffusion Cu into CdTe thick film by annealing for optoelectronics

Abstract In the present study, thermal evaporation techniques were used to prepare Cadmium Telluride (CdTe) films with thickness 1 μm on a glass substrate (at constant temperature150 °C). By immersing these films in a solution Cu(NO3)2 (1g/1000ml) for 30 min, the prepared films were doped by ion exchange with Cu. Furthermore, the doped films were annealed in vacuum at different temperatures (25, 125, 250, 375, and 500 °C) for the diffusion of dopant Cu content, for 30 min. Using the method of Swanepoel, the film thickness as well as the refractive index of films was identified. The density functional theory (DFT-TDDFT) by DMol3 was used for the optimization of CdTe and Cu:CdTe as an isolated molecule in the gaseous phase. From using the DMol3/(GGA-PW91) method with DFT-TDDFT simulation, the HOMO and LUMO values for CdTe and Cu:CdTe isolated molecule are 2.41 eV and 1.66 eV, respectively. The MEP computations and Quantum-chemical calculations properties are computed and combined with the experimental study by using DMol3/(GGA-PW91) software. The possible transition in these as deposited and treated films are found to allow direct transition with reduction of the band gap from 1.50 to 1.37 eV with an increase of the temperature of the annealing. Dielectric constant, Energy loss functions (VELF and SELF) for CdTe as deposited and treated were addressed in terms of temperature rise in the annealing. The energy gap is also determined using photoluminescence (PL) and its values the corresponding wavelength peaks correspond roughly to the energy obtained through optical studies.