Effects of uniaxial strain on structural, electronic, and optical properties of LiNbO3: Ab-initio calculations

Abstract

The semiconductor LiNbO3 has recently attracted a great deal of interest in the material science community. In this study, the effect of uniaxial strain Ɛc on the structural and optoelectronic properties of the material is studied by the first-principles full-potential linearized augmented plane wave method. The results are obtained in a density functional theory (DFT) framework, using a generalized gradient approximation (GGA-PBE) based on total energy minimization, as implemented in the WIEN2k code. The research results show that the unstrained LiNbO3 is an indirect band gap semiconductor with energy of 3.544 eV, which improves the results of some previous DFT calculations, but is still lower than the experimental data. It is found that the strain between −8% and +8% will affect the value of the LiNbO3 band gap. In fact, the results show that the electronic properties are closely related to the external compressive and tensile stress (CTS), causing the electronic band gap of LiNbO3 to increase and decrease, indeed the gap energy goes from 3.119 eV for 8% to 3.746 eV for −8%. The optical coefficients in the in both x-z directions are studied. For unstrained LiNbO3 they are similar but significantly distinct. The applied uniaxial strain increases the anisotropy significantly, and the difference between the xx and zz directions becomes much larger. It has also been found that strain can cause considerable changes in the optical band gap of the material. In addition, the absorption capacity and optical conductivity is improved under tensile stress, which is more efficient and more suitable for optical applications in the visible and ultraviolet spectrum.