Optimization Optoelectronic Properties ZnxCd1-xTe System for Solar Cell Application: Theoretical and Experimental Study

Abstract

Within the framework of the density functional theory (DFT) using the Wien2k package and the method of linear extended plane waves (FP-LAPW), quantum mechanical calculations were implemented to study the structural, electronic, and optical properties of the ZnxCd1-xTe system in the full range of 0≤x≤1 with a step of 0.25. To determine the optimal volume and grid parameters, the calculation of the total energy of semiconductor nanocomposites CdTe, Zn0.25Cd0.75Te, Zn0.5 Cd0.5 Te, Zn0.75Cd0.25Te, and ZnTe, the generalized gradient approximation (GGA) was applied, which is based on relaxation (optimization) of the volume and minimization of energy (finding the energy of the ground state). According to our calculations within the framework of the DFT, with an increase in the Zn concentration, the constant lattice parameters and the size (volume) of these nanocrystals decrease and are in good agreement with the results obtained this work by the method of X-ray structural analysis. The calculated band gaps of these nanocrystals using the modified exchange-correlation potential mBJ tend to increase, which agrees with the experimental data. The results of spin-polarized and spin-orbit calculations of the band structure showed that all these nanocrystals have direct transition points for electrons. After approximation by the least-squares method, empirical formulas were obtained to establish the concentration dependence of changes in the volumes and bandgap of Zn-modified nanocrystals, which will help experimenters obtain particles with certain sizes and bandgap. Such theoretical studies further open the possibility of accurate prediction of the electronic-energy properties of other semiconductor nanosized structures to develop and produce new nanomaterials with predetermined and programmed properties.