Hopping conduction in GaAs layers grown by molecular-beam epitaxy at low temperatures

The electrical conductivity of GaAs layers grown by molecular-beam epitaxy at low temperatures was studied by using the van der Pauw method. The electrical conductivity of thick GaAs layers grown at temperatures above 200 deg. C changes with the concentration of antisite As atoms following the nearest-neighbor hopping model. From the dependence of the conductivity on the average spacing of antisite As atoms, the Bohr radius of the donor wave function in the hydrogen like model was estimated to be between 2.8 and 4.0 A. The activation energy for hopping conduction changes inversely with the average distance of antisite As atoms. Enhanced incorporation of excess As occurs in the growth of ultrathin GaAs layers at low temperatures. The electrical resistivity of the ultrathin layers is reduced to nearly 1 Ω cm at room temperature by the enhanced incorporation. The activation energy for hopping conduction in the ultrathin layers is significantly lower than that expected from the inversely proportional relation with the average spacing of antisite As atoms