Amorphous Ge alloy films. II. Transport properties

Abstract

The electrical resistivity, its frequency and temperature dependence, and the thermoelectric power (TEP) and its temperature dependence are studied in amorphous films of Ge co-deposited with different concentrations of Cu, Fe, and Al. The electrical resistivity of Ge— Al films decreases gradually with increasing Al content. In contrast, the electrical resistivity of Ge—Cu and Ge—Fe films decreases rapidly with increasing concentration of the alloying element. The temperature dependence of the electrical resistivity of Ge—Al films indicates that, with increasing concentration of Al in Ge, the hopping conduction is appreciably reduced. For Al concentrations >5 at%, the electrical resistivity shows an exponential temperature dependence. In the case of Ge—Cu and Ge—Fe films, the activation energy of conduction decreases at all temperatures. For metal concentrations less than a few at% in Ge, the electrical resistivity decreases with increasing frequency. For higher concentrations, a frequency independent electrical resistivity is observed. GeAl films exhibit large positive TEP at all compositions. For large (>10 at%) concentrations, the TEP of Ge—Al films shows an exponential temperature dependence. In contrast to the behaviour of Ge—Al films, the TEP of Ge—Cu and GeFe films shows small (≈several μV/K) values for concentrations greater than a few at%. At concentrations >5 at% the weak temperature dependence of the electrical resistivity and the metallic-like TEP behaviour indicate the formation of an impurity band.