HOPPING CONDUCTION IN MOLECULAR-BEAM EPITAXIAL GAAS GROWN AT VERY-LOW TEMPERATURES

Conductivity and Hall effect measurements have been performed on 2 mum thick molecular beam epitaxial GaAs layers grown at very low substrate temperatures, 200 to 400-degrees-C. For growth temperatures below 300-degrees-C, the conduction is dominated by hopping between arsenic antisite defects of concentrations up to 10(-20) cm-3. Below measurement temperatures of about 130 K, the hopping conduction can be quenched by strong IR light illumination, because the antisite then becomes metastable. The antisite has a thermal activation energy of 0.65 +/- 0.01 eV, and thus is not identical to the famous EL2. Both nearest-neighbor and variable-range hopping mechanisms are considered in the analysis.