Diffusion and solubility of metal impurities in germanium

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The speed of silicon devices is increasingly limited bei the charge mobility of silicon. The higher charge mobility of germanium can greatly extend these limits but the commercial substitution of germanium for silicon is hindered by a lack of fundamental knowledge. The project wil dertermine the diffusion and solubility of several common transition metals in single-crystal germanium. The transition metals Fe, Co and Cr were chosen because of the serious contamination problems they cause in the production of Si/Ge wafers and in device processes where exposure to elevated temperatures ist required. Diffusion annealing will be mde by both furnace heating and rapid thermal processing. Impurity depth distributions will be measured by both radiotracer techniques and variabletemperature spreading-resistance profiling. The latter method will also provide data concerning the electric state of the impurity in the Ge matrix. The results will provide crucial information not only about the impurity solubility and diffusivity as a function of temperature but also about the preferred state of incorporation and the underlying diffusion mechanism. The characterisation of native point defects as diffusion vehicles in germanium is another goal of this proposal. This goal will be greatly helped by a cooperative effort with a group at Ghent University, Belgium, that is experts an the electric properties of transition metal impurities in Ge.