Dimensional crossover and weak localization in a 90 nm n-GaAs thin film.

We report on the magnetotransport in a 90 nm thick n-type GaAs epitaxial thin film in the weak localization (WL) regime. Low temperature (T</=50 K) magnetotransport data are fit with WL theory, from which the phase coherence time, tau(varphi) proportional, variantT(-p) (p=1.22+/-0.01), are extracted. We conclude that the dominant dephasing mechanism at these temperatures is electron-electron (e-e) scattering in the Nyquist limit. Evidence of a crossover from two-dimensional to three-dimensional behavior with respect to both coherent transport (WL) and e-e interactions is observed in the temperature dependence of the zero-field conductivity and tau(varphi), respectively.