Effect of Electron-phonon Scattering on the Thermal Conductivity of Si Nanowires

Even though the effect of electron-phonon scattering on the electronic properties of Si nanowires has been widely studied, its impact on phonon transport has received much less attention. Recent experiments gave the first evidence of a doping-induced reduction of the thermal conductivity in highly B-doped \pmb( ~ 5×10¹⁹ cm^-3) Si nanowires with a diameter of 31 nm. Here, we present a model that can fully explain these data. We also simulated the thermal conductivity of P-doped Si nanowires and found a smaller reduction compared to the B-doped samples. Our model includes the effect of incomplete ionization due to interface states, trapped charges, and the dielectric mismatch between nanowire and its surrounding. This effect is most pronounced close to a doping level of \pmb10¹⁸ cm^-3 for B- and P-doped Si nanowires with an electronic diameter of 31 nm at room temperature. In mitigating the dielectric mismatch, both an increasing diameter and coating the nanowire by an oxide reduce the effect of incomplete ionization. At high doping concentration (~5 × 10¹⁹cm^-3) it can be neglected.

I. Introduction

It is well-known that B and P dopants in bulk Si reduce its thermal conductivity in the low-temperature range [1], [2]. Therefore, the doping concentration could be another parameter to improve the figure of merit (ZT) of nanostructures when used as thermoelectric converters. Recent simulations [3] of the thermal conductivity of B-doped Si nanowires with a diameter of 31 nm did not match the experimental data because the effect of electron-phonon scattering was not taken into account. In this paper, electron-phonon scattering is included for the first time to calculate the thermal conductivity of B-and P-doped Si nanowires. The good agreement with the available experimental data validates the theoretical model.