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HL: Fachverband Halbleiterphysik

HL 30: Si/Ge

HL 30.13: Vortrag

Mittwoch, 25. März 2009, 12:45–13:00, POT 51

Properties of Vacancies in Germanium Probed by Fast Diffusing Transition Metals — Ludmila Lerner and •Nicolaas Stolwijk — Universität Münster, Institut für Materialphysik, 48149 Münster

The equilibrium concentration and diffusivity of vacancies (V) in Ge were assessed as a function of temperature from a detailed analysis of the diffusion behaviour of Co and Fe in electronic-grade Ge wafers. Surprisingly, it was found that the resulting equilibrium concentrations C_V^eq exceed the published experimental data by one order of magnitude. Accordingly, the diffusivities D_V fall below existing estimates by roughly a factor of ten in order to reproduce the well-established Ge self-diffusivity via the vacancy mechanism. In addition, the enthalpy of vacancy formation appears to be much smaller than the values calculated by ab initio theoretical methods.

Diffusion experiments were performed with the radiotracers ⁵⁷Co and ⁵⁹Fe over the temperature range 600-900 ^∘C. The sensitivity of Co and Fe diffusion for the vacancy properties of the Ge host lattice relies on the observation that these impurities migrate via the dissociative mechanism involving V-mediated interstitial-substitutional exchange. In particular, Co was found to be an interesting probe atom as it crosses the borderline - upon increase of temperature - between a V-controlled mode of diffusion and a Co-interstitial-controlled one. Also the fact that the solubility of substitutional Co proved to be similar in magnitude to C_V^eq constitutes a crucial feature in the evaluation of the V-related data.