Structural stability and electrical conductivity of amorphous Ge-metal alloy films

Abstract

Stable homogeneous amorphous alloy ∗ ∗ A homogeneous amorphous phase of Ge mixed with an impurity is termed here as an amorphous alloy. films of Ge with different concentrations of Al, Cu and Fe have been prepared by the simultaneous vapor deposition technique. Ge-Metal films are amorphous up to a concentration of ∼ 40 at.% Al, ∼ 20 at.% Cu and ∼ 20 at.% Fe. The cyclic annealing and crystallization temperature of these films show that whereas Al increases the stability of the amorphous phase, the addition of Cu and Fe decreases it. The electrical resistivity decreases gradually with increasing Al content. In contrast, a rapid decrease in the electrical resistivity is observed for the Ge-Cu and Ge-Fe systems. The thermoelectric power (TEP) of Ge-Cu and Ge-Fe system assumes small values ∼ few μV/deg for concentrations greater than few atomic percent. Ge-Al system exhibits large positive thermoelectric power at all compositions. The temperature dependence of the electrical resistivity of these alloy films show that the addition of Cu and Fe to Ge results in a drastic decrease in the activation energy of conduction whereas the addition of Al increases the activation energy. Ge-Al films exhibit intrinsic like conduction in the temperature range 100–300 K. The Ge-Cu and Ge-Fe films exhibit hopping conduction from 100–300 K and the related density of states is up to 100 times larger than in pure a-Ge films.