Electrical transport properties of Cu₃Ge thin films

We present results of electrical transport studies performed on thin films of ε1-Cu3Ge in the temperature range 4.2 - 300 K. It is found that ε1-Cu3Ge which has a long-range ordered monoclinic crystal structure, exhibits a remarkably low metallic resistivity of approx. 6 μΩ cm at room temperature. The density of charge carriers, which are predominantly holes, is approx. 8 × 1022/cm3 and is independent of temperature and film thickness. The Hall mobility at 4.2 K is approx. 132 cm2/V s, considerably higher than in pure copper. The elastic mean free path is found to be approx. 1200angstrom, which is surprisingly large for a metallic compound film. The results show that the residual resistivity is dominated by surface scattering rather than grain-boundary scattering. It is also found that by varying the Ge concentration from 0 to 40 at.% the resistivity exhibits anomalous behavior. This behavior is correlated with changes observed in the crystal structure of the thin-film alloys as the Ge concentration is increased. The resistivity remains close to that of the ε1-Cu3Ge phase over a range of Ge concentration which extends from 25 to 35 at.%.