Intervalley scattering and weak localization in Si-based two-dimensional structures

TL;DR

This study investigates weak localization magnetoresistance in Si MOS structures, extending theoretical models to account for two valleys, and finds that interface roughness significantly influences intervalley scattering.

Contribution

The paper extends weak localization theory to two-valley Si systems and analyzes the temperature-independent, strong intervalley scattering caused by interface roughness.

Findings

Intervalley scattering is elastic and strong.

Temperature dependence of phase-breaking time matches electron-electron interaction theory.

Intervalley scattering rate decreases with increasing electron density.

Abstract

We have measured the weak localization magnetoresistance in (001)-oriented Si MOS structures with a wide range of mobilities. For the quantitative analysis of the data, we have extended the theory of weak-localization corrections in the ballistic regime to the system with two equivalent valleys in electron spectrum. This theory describes the observed magnetoresistance and allows the extraction of the phase breaking time tau_phi and the intervalley scattering time tau_v. The temperature dependences tau_phi(T) for all studied structures are in good agreement with the theory of electron-electron interaction effects in two-dimensional systems. The intervalley scattering is elastic and rather strong: tau_v is typically only an order of magnitude greater than the transport time, tau. It is found that the intervalley scattering rate is temperature-independent and the ratio tau_v/tau decreases with increasing the electron density. These observations suggest that the roughness of the Si-SiO2 interface plays the major role in intervalley scattering.