Probing optical, phonon, thermal and defect properties of 3C–SiC/Si (001)

Abstract

Comprehensive results of experimental and theoretical studies are reported to probe the optical, phonon, thermal and defect properties of 3C–SiC/Si (001). By exploiting phonon-assisted Raman scattering (RS) spectroscopy we have recognized, among the conventional optical modes [TO(Γ) ~796cm−1 and LO(Γ) ~973cm−1], two extra phonon features near ~625cm−1 and 670cm−1 — possibly falling between the forbidden gap of the acoustic and optical branches. Temperature dependent profile of the unresolved ~670cm−1 band has indicated disordering by nearby defects and/or stress — rendering shorter phonon lifetime to instigate mode broadening. Accurate assessments of the lattice dynamical, thermal and defect properties are achieved by exploiting phonons from a rigid-ion model fitted to the inelastic x-ray scattering data and expending apposite group-theoretical selection rules. Lattice relaxations around Si/C atoms attained by the first-principles bond-orbital model for isolated defects have helped us to evaluate the necessary force constant variations for constructing perturbation matrices of the “complex-defect-centers”. For isolated anti-site CSi and SiC defects (Td-symmetry), our methodical Green's function (GF) theory has predicted triply degenerate F2 gap modes near 630cm−1 and 660cm−1, respectively. The GF simulations of impurity vibrations for a neutral nearest-neighbor anti-site SiC–CSi pair-defect (C3v-symmetry) provided gap-modes to appear within the broad ~670cm−1 band at 664.8cm−1 (a1) and 660.6cm−1 (e). The calculated results of localized vibrational modes are compared and discussed with phonon features observed in the RS experiments as well as with the density function theory.