Structural properties of polycrystalline Ge-metal films

Abstract

Polycrystalline Ge-metal films with 0.5 to 10 at% concentration of Al. Ga. Ag. Au. Cu. and Fe are prepared by codepositing onto glass/rock salt substrates held at 723 K and also by crystallizing amorphous films of the same materials by heating at 723 K. The structural details of these films are established by transmission electron microscopy and electron diffraction. For metal concentrations ≤5 at%, the electron diffraction patterns of these films are essentially similar to that of pure Ge. The grain size decreases rapidly with increasing concentration of the metal. Beyond 5 at%, segregation of the metal and compound formation determine the structural properties. In the case of Al which has a finite solubility in Ge, the lattice constant decreases and the grain size is nearly independent of metal concentration. In the case of Ag and Au which have negligible solubility in Ge, the films are heterogeneous having segregated metal particles, and the grain size decreases rapidly. The diffraction pattern corresponding to a mixture of Ge and Cu₃Ge and ordered phases/compounds of Fe with Ge are observed in the Ge—Cu and Ge—Fe films and the grain size increases with metal concentration.