Identification of a donor state of substitutional cadmium in silicon

The structural and electronic properties of cadmium in p-type silicon were studied by means of EPR. Cd was diffused in one set of samples whereas in a second set we used high energy implantations in the MeV range for doping, followed by a high temperature annealing step at 1200 degrees C. The angula r variations of the corresponding spectra show cubic symmetry and can be ex plained with an S = 3/2 orbital singlet ground state. From comparison of th e EPR results obtained from samples with different shallow p-dopants (B, Al , Ga, In) and doping levels it can be concluded, that the spectra arise fro m the Cd+ donor state with an energy level above the In acceptor level. The se experimental findings were compared with theoretical predictions of elec tronic structure calculations based on the Local Density Approximation of t he Density Functional Theory using the LMTO-ASA scheme. The comparison show s that the donor state must be due to substitutional Cd.