Papers by Keyword: Phonon Confinement

Abstract: Modified Callaway's theory was used to calculate lattice thermal conductivity (LTC) of Germanium nanowires. Results are compared to those of experimental values of the temperature dependence of LTC for nanowire diameters of 62, 19, and 15nm. In this calculation, both longitudinal and transverse modes are taken into account. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Effect of parameters, phonon confinement and imperfections in limiting thermal conductivity for the nanowires under considerations are investigated. The suppression in thermal conductivity of these nanowires is arise from electron-phonon scattering and phonon-boundary scattering at low temperatures, while at high temperatures is due to imperfections and intrinsic properties.

Abstract: In the framework of effective mass approximation, the LandauPekar variational procedure is adopted to study the ground-state binding energy of a hydrogenic impurity in a semiconductor nanowire with finite confining potential subjected to both external fields (electric and magnetic) and electronpolar optical phonon interaction taking into account the phonon confinement effect. The results for the binding energy as well as polaronic correction are obtained as a function of the wire radius, impurity position and applied fields. Calculated results reveal that the values of the polaronic shifts of impurity binding energy can be quite different for cases with finite and infinite confining potentials.

Abstract: The effect of phonon confinement and impurity doping in silicon nanowires (SiNWs) synthesized by laser ablation were investigated. The diameter of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs’ surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical phonon peak due to phonon confinement. Boron doping was also performed during the growth of SiNWs. Local vibrational modes of boron (B) in silicon nanowires (SiNWs) synthesized by laser ablation were observed at about 618 and 640 cm–1 by Raman scattering measurements. Fano broadening due to coupling between discrete optical phonons and the continuum of interband hole excitations was also observed in the Si optical phonon peak. These results prove that B atoms were doped in the SiNWs.