Electrical and Structural Properties of Amorphous Germanium

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Abstract
The electrical conductivity of amorphous Ge films ranging in thickness between 240 Å and 6 μm was measured both in the plane and in the transverse directions. The Ge films were deposited by the getter-sputtering technique onto sapphire and glass substrates at the following temperatures: 573, 300, 170, and 77 °K. Transmission electron microscopy and x-ray diffraction were used to characterize the defect structure of films deposited by this technique and in this regard structural variations as a function of film thickness, substrate temperature, and substrate material were investigated. Most of the conductivity measurements were made on films deposited and kept at 77 °K; the annealing behavior of such films led to a better understanding of the defect structure and its influence on electrical properties. Marked differences were observed in electrical properties between films deposited at 300 °K and films deposited at 77 °K, which are related to the defect structure of the films. A marked anisotropy in both the resistivity and its temperature dependence was observed below 0.4 μm; this anisotropy increased with decreasing film thickness down to the thinnest film studied (240 Å).