Electron-acoustic-phonon interaction in core/shell Ge/Si and Si/Ge nanowires

TL;DR

This paper derives analytical expressions for electron- and hole-phonon interactions in Ge/Si and Si/Ge core/shell nanowires, analyzing how spatial confinement and interface strain affect phonon properties and electron-phonon coupling.

Contribution

It provides the first analytical framework for understanding acoustical phonon interactions in core/shell nanowires with circular cross sections.

Findings

Confined effects alter phonon displacement and dispersion.

Bulk velocities are renormalized by confinement and strain.

Shell presence influences phonon dispersion and coupling.

Abstract

General expressions for the electron- and hole-acoustical-phonon deformation potential Hamiltonian (H_{E-DP}) are derived for the case of Ge/Si and Si/Ge core/shell nanowire structures (NWs) with circular cross section. Based on the short-range elastic continuum approach and on derived analytical results, the spatial confined effects on the vector phonon displacement, the phonon dispersion relation and the electron- and hole-phonon scattering amplitudes are analyzed. It is shown that the acoustical vector displacement, phonon frequencies and H_{E-DP} present mixed torsional, axial, and radial components depending on the angular momentum quantum number and phonon wavector under consideration. The treatment shows that bulk group velocities of the constituent materials are renormalized due to the spatial confinement and intrinsic strain at the interface. The role of insulating shell on the phonon dispersion and electron-phonon coupling in Ge/Si and Si/Ge NWs are discussed.