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

We have measured the weak localization magnetoresistance in (001)-oriented Si metal-oxide-semiconductor 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.