Structural dependence of percolation in germanium films

The critical volume fraction of percolation in conductivity has been determined for di-phasic Ge films. Unlike Si, two values were found, 0.15 and 0.4, corresponding respectively to low and high substrate temperatures. Furthermore, scanning electron microscopy revealed a random spherical growth for the former value as contrast to an essentially columnar growth for the latter. The higher and lower values are consistent with the theoretical limits for two- and three-dimensional percolation.