First-principles Prediction of Carrier Mobility in Semiconductor Nanowires Based on the Spatially Dependent Boltzmann Transport Equation

TL;DR

This paper develops an ab initio model to predict carrier mobility in semiconductor nanowires, accounting for surface scattering and spatial confinement, providing a benchmark for experimental and theoretical studies.

Contribution

It introduces a spatially dependent Boltzmann transport equation framework for nanowires, revealing the mobility-diameter relation and effects of various physical parameters.

Findings

Mobility decreases with decreasing nanowire diameter following a specific relation.

A boundary layer with significant mobility gradient is identified.

Theoretical predictions are higher than experimental data, highlighting potential structural imperfections.

Abstract

Carrier mobility in bulk semiconductors is typically governed by electron-phonon (e-ph) scattering. In nanostructures, spatial confinement can lead to significant surface scattering, lowering mobility and breaking the spatial homogeneity assumption of conventional models. In this work, a fully ab initio framework based on the spatially dependent Boltzmann transport equation for one-dimensional nanowires is developed. We apply it to Si and GaN assuming diffusive surface scattering, and reveal the mobility-diameter relation: $\mu_\mathrm{1D} = \mu_\mathrm{bulk} \left[1-\left(d/d_0\right)^{-\beta}\right]$. The parameter $d_0$, comparable to the carrier mean free path, defines a boundary layer exhibiting a considerable mobility gradient, and also quantifies the competition between e-ph and surface scattering together with $\beta$. We further discuss the effects of orientation, cross-sectional shape, and temperature. Moreover, experimental data are generally lower than our predictions, possibly due to structural imperfections, systematic errors from measurements, etc. Therefore, our theoretical method can provide an intrinsic benchmark toward optimized experimental realizations.