Optical and electronic properties of SiTex (x=1, 2) from first-principles

The optical and electronic properties of alpha-SiTe, beta-SiTe, and RX-SiTe2 are investigated. A detailed analysis of electronic properties is done using standard density functional theory (DFT) and hybrid functional methods. The static dielectric properties are investigated using the density functional perturbation theory method. The optical properties are studied under three different methods: standard DFT, many-body Green's functions, and the Bethe-Salpeter equation. Our calculations show that the SiTe compounds possess extremely high static dielectric constants in their bulk forms [epsilon(0)(perpendicular to) = 68.58 and epsilon(0)(||) = 127.29 for alpha-SiTe, and epsilon(0)(perpendicular to) = 76.23 and epsilon(0)(||) = 74.61 for beta-SiTe]. The frequency-dependent dielectric functions Im(epsilon) have very large values (>100) in the optical regime, which are among the highest of layered materials, suggesting them as excellent light absorbents in the corresponding frequencies. alpha-SiTe exhibits a high degree of optical anisotropy as compared to the other two compounds, consistent with their structural configurations. A strong interlayer excitonic effect is observed in bulk RX-SiTe2. In addition, an analysis of Raman intensity is also performed.