Devki N Talwar
Indiana University of Pennsylvania, USA
Title: Optical properties of 3C–SiC/Si (001) defect microstructures by exploiting Raman scattering and X-ray absorption fine structure measurements
Biography
Biography: Devki N Talwar
Abstract
We report comprehensive studies of the optical and structural properties of microstructures in V-CVD grown 3C–SiC/Si (001) epifilms by exploiting Raman scattering and X-ray absorption fine structure measurements. By exploiting the phonon-assisted Raman scattering spectroscopy we have recognized the conventional optical modes ~794 cm-1, 973 cm-1 and two additional phonon features near ~ 625 cm-1 and 670 cm-1 - possibly falling between the forbidden gap of the acoustic and optical branches of 3C-SiC. Synchrotron radiation X-ray absorption fine-structure (SR-XAFS) measurements are performed by exploiting a double-crystal monochromator beamline at the National Synchrotron Radiation Research Center, Hsinchu, Taiwan. The measured X-ray absorption spectra are carefully examined to check the ability of experimental standards with the ab initio calculations. Temperature dependent profile of the unresolved ~670 cm-1 Raman band indicates disordering by defects and/or stress that makes phonon lifetime shorter to instigate mode broadening. Accurate assessments of 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 first-principles bond-orbital model for isolated defects have helped evaluating the necessary force constant variations to construct perturbation matrices of “complex-defect-centers”. For the isolated intrinsic CSi and SiC defects (Td-symmetry) our methodical greens function (GF) theory predicted triply degenerate F2 gap modes near ~630 cm-1 and ~660 cm-1, respectively. The GF simulations of impurity vibrations for a neutral “anti-site” CSi-SiC pair (C3v-symmetry) provided gap-modes to appear within the broad ~670 cm-1 band at 664.8 cm-1 (a1) and 660.6 cm-1 (e). These outcomes implying possible links of ASP defect to a proto-typical DI center in 3C-SiC are compared and deliberated against the existing experimental data.