2.3 Investigations of metal contacts to amorphous evaporated Ge films

Amorphous Ge films are used as non-injecting ohmic contacts to high-resistivity n-silicon radiation detectors, but the function of this contact is not yet fully explored. One part problem is the role of the metal films used as external contacts to the amorphous film. In this paper we investigate the function of different contacting metals, such as Au, Al, Cr by measuring the I-V-characteristics of sandwich structures with two metals on both sides of the amorphous evaporated Ge film (of typical thickness 1 μm). It was found that while the symmetric CrGeCr structure (also AuGeAu) had low resistance (leading to resistivity values of ?4 × 10⁴ωcm for the Ge film), the unsymmetric structures e.g. AlGeCr and AlGeAu, showed higher resistance. This was again found for the AlGeAl structure, which also showed some polarity dependence. Rutherford backscattering was used to investigate diffusion effects between the layers; also the microstructure of the Ge films was investigated by electron microscopy.