HOPPING CONDUCTION IN MOLECULAR-BEAM EPITAXIAL GAAS GROWN AT VERY-LOWTEMPERATURES

Conductivity and Hall effect measurements have been performed on 2 mum thick molecular beam epitaxial GaAs layers grown at very low substrat e temperatures, 200 to 400-degrees-C. For growth temperatures below 30 0-degrees-C, the conduction is dominated by hopping between arsenic an tisite defects of concentrations up to 10(-20) cm-3. Below measurement temperatures of about 130 K, the hopping conduction can be quenched b y strong IR light illumination, because the antisite then becomes meta stable. 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.