Hot electron diffusion, microwave noise, and piezoresistivity in Si from first principles

TL;DR

This study uses first-principles calculations to analyze hot electron diffusion, microwave noise, and piezoresistivity in silicon, revealing discrepancies with experimental data likely due to factors beyond electron-phonon interactions.

Contribution

It provides the first ab-initio calculations of silicon's hot electron diffusion coefficient and investigates the role of scattering and other effects on transport properties.

Findings

Qualitative trends match experimental observations at high fields.

Quantitative discrepancies suggest additional factors influence diffusion.

f-type scattering strength is not the main cause of diffusion discrepancies.

Abstract

Ab-initio calculations of charge transport properties in materials without adjustable parameters have provided microscopic insights into electron-phonon interactions which govern charge transport properties. Other transport properties such as the diffusion coefficient provide additional microscopic information and are readily accessible experimentally, but few ab-initio calculations of these properties have been performed. Here, we report first-principles calculations of the hot electron diffusion coefficient in Si and its dependence on electric field over temperatures from 77 -- 300 K. While qualitative agreement in trends such as anisotropy at high electric fields is obtained, the quantitative agreement that is routinely achieved for low-field mobility is lacking. We examine whether the discrepancy can be attributed to an inaccurate description of f-type intervalley scattering by computing the microwave-frequency noise spectrum and piezoresistivity. These calculations indicate that any error in the strength of f-type scattering is insufficient to explain the diffusion coefficient discrepancies. Our findings suggest that the measured diffusion coefficient is influenced by factors such as space charge effects which are not included in ab-initio calculations, impacting the interpretation of this property in terms of charge transport processes.