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The low effective mass of holes in Ge has opened up the possibility of using Ge in ultrafast complimentary metal-oxide-semiconductor devices [1]. To exploit the advantages of germa-nium an appropriate contact technology will have to be developed. Analogous to the silicon based technology, where metal silicides are used to obtain low-resistance contacts, contacts made of metal germanides could exhibit low sheet and contact resistance, good stability after heat treatment and could be formed by means of simple technological processes like thermal evaporation at low temperatures. Data concerning the behaviour of metal thin films on ger-manium upon thermal treatment are relatively scarce. The thin film reaction of 20 transition metals with germanium substrates has been reported [2]. It was found that among the investi-gated materials Ni and Pd were the most promising candidates, because the formation of NiGe and PtGe at low temperatures lead to contacts with low resistivity, limited film roughness, sufficient thermal stability and limited sensitivity to oxidation. The formation of particularly NiGe contacts has been investigated in some detail [3].
In this work we report on a systematic study of the interaction between thin gold films and crystalline germanium substrates. Gold metal films having thicknesses of 30 and 100 nm have been prepared by means of thermal evaporation on bulk-grown (111) n-type germanium doped with Sb to a level of 2.5„e1015 cm-3.. Before metallization the samples were first de-greased and then etched in a mixture of H2O2:H2O (1:5) for one minute. Subsequently the samples have been thermally treated in Ar-atmosphere for 10 minutes and at temperatures ranging from 300 to 600¢XC. Rutherford backscattering spectrometry (RBS) has been per-formed to estimate the composition of the as-deposited and thermally treated films. It was found, that the composition of the as-deposited film remains unchanged under thermal treat-ment up to 350¢XC. Between 350¢XC and 370¢XC a gold rich layer containing a very small amount of germanium is formed. At 370¢XC this layer suddenly converts in a germanium rich layer with a small amount of gold. This transition is connected with the formation of agglom-erates on the surface of the substrate.
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