Electrical Properties and Anisotropy in Amorphous Si andSi0.5Ge0.5Alloy

The electrical conductivity of amorphous Si films ranging in thickness between 610 Å and 2.2 μm was measured both in the plane and in the transverse directions. A similar although briefer study was performed on amorphous ${\mathrm{Si}}_{0.5}$ ${\mathrm{Ge}}_{0.5}$ films. The films were deposited at 300 and 77 °K by the getter-sputtering technique. The major portion of the study was conducted on films deposited and kept at 77 °K: There are marked differences in electrical properties between films deposited at 300 °K and films deposited and kept at 77 °K, which were related to the structure of the films. While a marked anisotropy in both the resistivity and its temperature dependence was previously reported for Ge, one only notices an anisotropy in the temperature dependence with Si films below 2500 Å; this anisotropy increases with decreasing film thickness down to the thinnest film studied (610 Å). In general, one can state that the electrical properties of ${\mathrm{Si}}_{0.5}$ ${\mathrm{Ge}}_{0.5}$ are intermediate between those of Si and Ge and that the anisotropy, if present at all, is very small and develops below 1200 Å.