Giant persistent photoconductivity induced crossover from strong to weak localization in Si-δ-doped GaAs compensated with Be acceptors

We present the results of measurements of two-dimensional electron transport in Si-δ-doped GaAs samples compensated with Be acceptors. It is shown that the temperature dependence of longitudinal resistivity Rxx in the interval 1 K–100 mK is well described by the variable-range-hopping mechanism Rxx(T)=R0 exp[(T0/T)1/2] peculiar for strongly localized electrons. Transitional illumination of these samples by a red light causes a persistent photoconductivity (PPC), which is fully determined by irreversible increase of electron mobility. As a result of illumination, parameter T0 decreases which leads to a giant exponential increase of PPC at low temperatures. After high dose of illumination, the temperature dependence of conductivity changes from exponential to logarithmic law, which can be considered as a crossover from strong to weak electron localization.