Linear temperature behavior of thermopower and strong electron-electron scattering in thick F-doped SnO$_{2}$ films

TL;DR

This study reveals that F-doped SnO₂ thick films exhibit linear thermopower behavior and dominant electron-electron scattering at low temperatures, with transport properties consistent with free-electron models and suppressed phonon-drag effects.

Contribution

It provides experimental validation of electron-electron scattering dominance and free-electron-like behavior in thick F-doped SnO₂ films, with quantitative testing of scattering rates.

Findings

Resistivity follows Bloch-Grüneisen law from 90 to 300 K.

Thermopower varies linearly with temperature from 10 to 300 K.

Electron-electron scattering dominates at low temperatures.

Abstract

Both the semi-classical and quantum transport properties of F-doped SnO$_2$ thick films ($\sim$1\,$\mu$m) were investigated experimentally. It is found that the resistivity caused by the thermal phonons obeys Bloch-Gr\"{u}neisen law from $\sim$90 to 300\,K, while only the diffusive thermopower, which varies linearly with temperature from 300 down to 10\,K, can be observed.The phonon-drag thermopower is completely suppressed due to the long electron-phonon relaxation time in the compound. These observations, together with the temperature independent characteristic of carrier concentration, indicate that the conduction electron in F-doped SnO$_2$ films behaves essentially like a free electron. At low temperatures, the electron-electron scattering dominates over the electron-phonon scattering and governs the inelastic scattering process. The theoretical predicated scattering rates for both large- and small-energy-transfer electron-electron scattering processes, which are negligibly weak in three-dimensional disordered conventional conductors, are quantitatively tested in this lower carrier concentration and free-electron-like highly degenerate semiconductor.