A. V. Krivosheeva

Electronic structure of stressed CrSi2

Abstract We present electronic properties of CrSi 2 under isotropic and anisotropic stress. Theoretical calculations were performed using the full-potential linearized-augmented-plane-wave method. The isotropic stress of the crystal leads to an almost linear variation of the direct and indirect transitions as a function of the lattice parameter, whereas anisotropic deformations result in more complicated dependencies. Uniaxial stretching of the lattice up to 106% converts chromium disilicide into a direct-gap semiconductor with a fundamental gap of about 0.3 eV. The compression of the lattice up to 94% changes the symmetry of the transitions.

Theoretical study of defect impact on two-dimensional MoS2

Our theoretical findings demonstrate for the first time a possibility of band-gap engineering of monolayer MoS2 crystals by oxygen and the presence of vacancies. Oxygen atoms are revealed to substitute sulfur ones, forming stable MoS2−xOx ternary compounds, or adsorb on top of the sulfur atoms. The substituting oxygen provides a decrease of the band gap from 1.86 to 1.64 eV and transforms the material from a direct-gap to an indirect-gap semiconductor. The surface adsorbed oxygen atoms decrease the band gap up to 0.98 eV depending on their location tending to the metallic character of the electron energy bands at a high concentration of the adsorbed atoms. Oxygen plasma processing is proposed as an effective technology for such band-gap modifications.

Effect of stresses in electronic properties of chromium disilicide

A detailed theoretical study of electronic properties of chromium disilicide CrSi2 under isotropic and anisotropic pressure has been performed by means of linearized augmented plane wave method. It has been found that in case of isotropic deformation the indirect and first direct gaps decrease linearly with the rise of the pressure but with different rates. A similar behavior was observed for uniaxial stress, while this dependence is more complicated and not linear. When the crystal structure is being 106% stretched, chromium disilicide becomes a direct-gap semiconductor with energy gap of about 0.31 eV.

Electronic properties of thin BaSi2 films with different orientations

By means of ab initio calculations we have investigated surface energies and band structures of BaSi2 thin films with (001), (010), (100), (011), (101), (110), and (111) surfaces. It is found that BaSi2(111), (010), and (100) surfaces possess the smallest surface energies which are almost twice less than the ones of the other surfaces. All thin films with different orientations and thickness are shown to be semiconductors. The influence of quantum confinement effects on BaSi2 thin film band gaps has been traced indicating nontrivial behavior because of the presence of surface states which characterize the top/bottom of the valence/conduction bands. By implementing a simple effective mass approximation model we could define energy positions of surface states for some BaSi2 surfaces.

Computer simulation of electronic and magnetic properties of ternary chalcopyrites doped with transition metals

Electronic and magnetic properties of BeSiAs2 and BeGeAs2 ternary compounds with chalcopyrite structure doped with transition metals (Mn, Cr) have been theoretically studied from the first principles. The influence of the substitutional positions of impurity atoms and their type on the appearance of a ferromagnetic (FM) or antiferromagnetic (AFM) state has been analyzed. It was found that magnetic moment of the systems does not depend strongly on the concentration and distance between impurity atoms, while the most important factors observed are the impurity type and substitution sites. Configurations with Mn atoms in the II-group sites are energetically stable in the AFM state, whereas Cr-doped ones seem to be in the FM state. Substitution of IV-group positions by both metals results preferably in the FM state, however these positions are not energetically favorable in comparison with II-group ones. The spin polarization of doped materials is evaluated and their possible application in spintronics is analyzed.

Band gap modifications of two-dimensional defected MoS2

The changes in structural and electronic properties, occurring in one monolayer of MoS2 at different concentrations of oxygen atoms doping and vacancies are investigated by means of ab initio computer simulation. The substitution of sulphur atoms by oxygen ones reduces the band gap for high concentrations only, transforming direct-gap semiconductor into an indirect one, whereas a smaller concentration of oxygen practically does not influence the gap. The presence of sulphur vacancies strongly reduces the band gap, leading to bands overlapping at high concentration and appearance of new bands at the gap region, which are determined by Mo 4d states with the mixture of S 3p states, at low concentrations.

Effect of lattice deformation on semiconducting properties of CrSi2

The effect of isotropic and anisotropic deformation on electronic and optical properties of semiconducting chromium disilicide CrSi2 is studied by the method of augmented plane waves. The compound is found to be an indirect-gap semiconductor with a band gap width of about 0.3 eV. It is found that the deformation affects the transitions similarly; however, for anisotropic deformation this effect is strongly nonlinear, and the stretching of the lattice up to 106% along the axis a results in the occurrence of a direct transition.