Amorphous Ge alloy films. I. Structural properties

Abstract

Structure, cycling behaviour, and temperature and kinetics of the amorphous → crystalline transformation have been studied in amorphous films of Ge co-deposited with Cu, Fe, Al, or Te. Electron microscopy and electron diffraction studies show that these films have a homogeneous amorphous phase (and, therefore, termed here as a-Ge alloy films) up to a maximum concentration of ≈ 20 at% Cu, ≈ 20 at% Fe, ≈ 30 at% Al, and ≈85 at% Te. The crystallization temperature of the amorphous films decreases with increasing concentration of the alloying element with the exception of Al in which it is independent of concentration up to ≈20 at%. The temperature range in which the amorphous → crystalline transformation occurs decreases with increasing concentration of impurity. The resistivity changes, commonly observed in room temperature deposited a-Ge films on thermal cycling, are arrested by the addition of Te. On the other hand, the thermal cycling of Ge-Al alloy films results in an increase in the resistivity and activation energy of conduction in a way similar to that observed in the case of a-Ge. The thermal cycling of Ge-Cu and Ge-Fe alloy films increases the resistivity, but the activation energy of conduction remains unchanged.