Electrical properties of Te-implanted GaAs

Tellurium was implanted into Cr-doped GaAs at 250 degreeC to a dose of 1013 or 1014 Te/cm2 at 120 keV. Sheet-resistivity and Hall-effect measurements were made on the samples for annealing temperatures up to 900 degreeC. From the temperature dependence of the sheet resistivity, the conduction mechanism of as-implanted samples was found to be due to thermally assisted tunneling in disordered semiconductors. The very small activation energy of <0.1 meV obtained from the sheet-resistivity curves for isochronal annealing temperatures of approximately-less-than200 degreeC indicates that formation of an amorphous layer has been prevented and that the samples have undergone no epitaxial recrystallization. Annealing at > or =600 degreeC produced n-type conductivity with the maximum effective bulk concentration being approx.1018 electrons/cm3 for the 1014 Te/cm2 sample annealed at 800 degreeC. However, the electrical compensation remained high (N/subA//N/subD/ approx. =0.6) for annealing temperatures ranging from 600 to 900 degreeC, the compensating centers being of the V/sub Ga/Te-complex type. The temperature dependence of the electrical characteristics for well-annealed samples resembled that of bulk material. However, a somewhat larger value of donor ionization energy (approx.7 meV) was obtained for the 1013 Te/cm2 sample annealed at 800 degreeC; this value may arise from the profiling effects