We assessed the equilibrium concentration (CVeq) and diffusivity (DV) of vacancies (V) in Ge as a function of temperature from a detailed analysis of the diffusion behavior of Co in electronic-grade Ge wafers. Diffusion experiments were performed with the radiotracer 57Co over the temperature range 650–900 °C using short-term isothermal lamp annealing and mechanical sectioning. The sensitivity of Co diffusion for the vacancy properties of the Ge host lattice relies on substantial evidence that Co migrates via the dissociative mechanism involving V-mediated interstitial-substitutional exchange. Co turned out to be a particularly interesting probe atom, as its diffusion behavior shows a crossover from a Co-interstitial-controlled mode at high temperatures to a V-controlled mode at lower temperatures. Also, the finding that the solubility of (substitutional) Co proved to be similar in magnitude to CVeq constitutes a crucial feature in the evaluation of the V-related data. Surprisingly, it was found that the deduced CVeq values exceed the literature data by one order of magnitude or more. Consistently, DV falls below existing estimates by roughly a factor of ten in order to reproduce the well-established Ge self-diffusivity due to the vacancy mechanism. Furthermore, our analysis yields a low value (∼0.5 eV) for the enthalpy of vacancy formation, which is at variance with the results from ab initio theoretical calculations.

Diffusion of Ir into Si was investigated in the temperature range from 875 to 1050 °C by means of neutron activation analysis and mechanical sectioning. Within the framework of interstitial-substitutional diffusion, previously established for Ir in Si, the measured penetration profiles were simulated by the simultaneous action of the kick-out mechanism and the dissociative mechanism. This enabled us to assess Si vacancy concentrations in thermal equilibrium.

Diffusion of the transition metals Co, Fe, and Cr into single-crystal germanium is found to be fast processes at temperatures relevant to the fabrication of semiconductor devices. These results were obtained from experiments in which electronic-grade Ge samples were provided with a radioactive surface source and short time annealed in a lamp furnace at temperatures ranging from 600to900°C. Diffusion coefficients were determined from penetration profiles of the radioisotopes Co57, Fe59, and Cr51. The results are interpreted within the framework of interstititial-substitutional diffusion and compared with earlier diffusion data on Ge crystals.

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