Annealing of Cd-implanted GaAs: Defect removal, lattice site occupation, and electrical activation

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Abstract
A systematic investigation of the behavior of Cd‐implanted GaAs after rapid thermal annealing is presented. The use of various experimental techniques gives a detailed picture regarding the annealing process in the low‐dose regime (1012 and 1013 cm−2) on a microscopic as well as on a macroscopic scale. Perturbed angular correlation experiments, using the radioactive probe 111mCd, yield information on the immediate environment of the Cd implant on an atomic scale. Rutherford backscattering channeling and photoluminescence spectroscopy give complementary information concerning the overall damage level in the implanted layer, Hall measurements are used to determine the degree of electrical activation of the implanted Cd acceptors. The outdiffusion of the implanted radioactive Cd atoms is also investigated. The removal of defects in the next‐nearest neighborhood of the Cd atoms takes place after annealing at 700 K and is accompanied by a general recovering of the crystal lattice. Between 600 and 900 K more distant defects are removed. The observed outdiffusion of about one‐third of the dopant atoms after annealing above 600 K is discussed in context with their partial incorporation in extended defects. Although already at 700 K, 80% of the implanted Cd atoms are on substitutional lattice sites with no defects in their immediate environment, an annealing temperature in excess of 1000 K is necessary to obtain electrical activation of the implants. It is concluded that compensating defects, present in ion‐implanted GaAs, are the reason for the significantly higher temperature required for electrical activation as compared to the incorporation of the dopants on defect‐free, substitutional lattice sites.

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