Electron transport in low temperature grown GaAs

GaAs grown at low temperature exhibits features, such as high resistivity, large breakdown voltage and short photoexcited carrier lifetime, that make it interesting for several device applications. Despite detailed studies of its electrical properties, the mechanism for electron transport has not been definitively determined and thus the debate on the origin for its high resistivity is not settled. Consequently, we have undertaken an impedance spectroscopy study, monitoring the admittance Y versus the pulsation ω of the electric field (from 5 to 13 MHz) and temperature (in the range 300–450 K), in materials grown at various temperatures and submitted to annealing treatments. The data obtained clearly demonstrate that electron transport is the result of a hopping process (the admittance varies linearly with ω) occurring in a partially filled band. The thermal activation of electrons into the conduction band gives the energetical location in the gap, from which we deduce that the EL2 defect is at the origin of the band in which hopping occurs. Moreover, the complete variation Y(ω) is characteristical of a percolation regime which demonstrates that conduction occurs around insulating regions.