Cross-sectional dependence of electron mobility and lattice thermal conductivity in silicon nanowires

• Published in: Journal of computational electronics 2008-09, Vol.7 (3), p.319-323
• Main Authors: Ramayya, E. B., Vasileska, D., Goodnick, S. M., Knezevic, I.
• Format: Article
• Language: English
• Subjects: Boltzmann transport equation; Cross sections; Cross-disciplinary physics: materials science; rheology; Electrical Engineering; Electrical resistivity; Electron mobility; Electrons; Engineering; Exact sciences and technology; Figure of merit; Heat conductivity; Heat transfer; Lattices; Materials science; Mathematical and Computational Engineering; Mathematical and Computational Physics; Mechanical Engineering; Nanoscale materials and structures: fabrication and characterization; Nanowires; Optical and Electronic Materials; Phonons; Physics; Quantum wires; Scattering; Scattering cross sections; Silicon; Theoretical; Thermal conductivity; Thermoelectric materials; Thermoelectricity
• ISSN: 1569-8025; 1572-8137
• DOI: 10.1007/s10825-008-0195-5

The thermoelectric efficiency of a material depends on the ratio of its electrical and thermal conductivity. In this work, the cross-sectional dependence of electron mobility and lattice thermal conductivity in silicon nanowires has been investigated by solving the electron and phonon Boltzmann transport equations. The effects of confinement on acoustic phonon scattering (both electron–phonon and phonon–phonon) are accounted for in this study. With decreasing wire cross-section, the electron mobility shows a non-monotonic variation, whereas the lattice thermal conductivity exhibits a linear decrease. The former is a result of the decrease in intervalley and intersubband scattering due to a redistribution of electrons among the twofold-degenerate Δ 2 and fourfold-degenerate Δ 4 valley subbands when the cross-section is below 5×5 nm 2 , while the latter is because of the monotonic increase of three phonon umklapp and boundary scattering with decreasing wire cross-section. Among the wires considered, those with a cross-section between 3×3 nm 2 and 4×4 nm 2 have the maximal ratio of the electron mobility to lattice thermal conductivity, and are expected to provide the maximal thermoelectric figure of merit.