Stability, electronic and phononic properties of beta and 1T structures of SiTex (x=1, 2) and their vertical heterostructures

By performing first-principles calculations, we predict a novel, stable single layer phase of silicon ditelluride, 1T-SiTe2, and its possible vertical heterostructures with single layer beta-SiTe. Structural optimization and phonon calculations reveal that 1T-SiTe2 structure has a dynamically stable ground state. Further analysis of the vibrational spectrum at the Gamma point shows that single layer 1T-SiTe2 has characteristic phonon modes at 80, 149, 191 and 294 cm(-1). Electronic-band structure demonstrates that 1T-SiTe2 phase exhibits a nonmagnetic metallic ground state with a negligible intrinsic spin-orbit splitting. Moreover, it is shown that similar structural parameters of 1T-SiTe2 and existing beta-SiTe phases allows construction of 1T-beta heterostructures with a negligible lattice mismatch. In this regard, it is found that two energetically favorable stacking orders, namely AA and A(T)B, have distinctive shear and layer breathing phonon modes. It is important to note that the combination of semiconducting beta-SiTe and metallic 1T-SiTe2 building blocks forms ultra-thin Schottky barriers that can be used in nanoscale optoelectronic device technologies.