ANNEALING OF CD-IMPLANTED GAAS - DEFECT REMOVAL, LATTICE SITE OCCUPATION, AND ELECTRICAL ACTIVATION

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 (10(12) and 10(13) cm-2) on a microscopic as well as on a macroscopic scale. Perturbed angular correlation experiments, using the radioactive probe Cd-111m, yield information on the immedia te environment of the Cd implant on an atomic scale. Rutherford backsc attering channeling and photoluminescence spectroscopy give complement ary information concerning the overall damage level in the implanted l ayer, Hall measurements are used to determine the degree of electrical activation of the implanted Cd acceptors. The outdiffusion of the imp lanted radioactive Cd atoms is also investigated. The removal of defec ts 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 c rystal lattice. Between 600 and 900 K more distant defects are removed . The observed outdiffusion of about one-third of the dopant atoms aft er annealing above 600 K is discussed in context with their partial in corporation in extended defects. Although already at 700 K, 80% of the implanted Cd atoms are on substitutional lattice sites with no defect s in their immediate environment, an annealing temperature in excess o f 1000 K is necessary to obtain electrical activation of the implants. It is concluded that compensating defects, present in ion-implanted G aAs, are the reason for the significantly higher temperature required for electrical activation as compared to the incorporation of the dopa nts on defect-free, substitutional lattice sites.