Abstract
Tellurium was implanted into Cr-doped GaAs at 250 °C 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 °C. 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 ≲200 °C indicates that formation of an amorphous layer has been prevented and that the samples have undergone no epitaxial recrystallization. Annealing at ?600 °C produced n-type conductivity with the maximum effective bulk concentration being ∼1018 electrons/cm3 for the 1014 Te/cm2 sample annealed at 800 °C. However, the electrical compensation remained high (NA/ND ?0.6) for annealing temperatures ranging from 600 to 900 °C, the compensating centers being of the VGaTe-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 (∼7 meV) was obtained for the 1013 Te/cm2 sample annealed at 800 °C; this value may arise from the profiling effects.
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