STRUCTURAL AND OPTOELECTRONIC PROPERTIES OF INDIUM-DOPED ALPHA-GE-H THIN-FILMS

This work reports on the structural, optical, and transport properties of rf sputtered In-doped hydrogenated amorphous germanium thin films. It has been found that the incorporation of In induces important changes in the optoelectronic properties of the films. The experimental results may be explained in terms of acceptor levels produced by tetrahedrally coordinated In, in a way similar to In doping of c-Ge. The transition from n-type conduction of as-deposited samples to p-type conduction has been monitored through thermopower measurements. Indium concentrations of the order of 1% induce the pinning of the Fermi energy at 0.45 eV above the valence band edge and a thermally activated conductivity at room temperature having an activation energy of a few meV. The effect is explained in terms of nearest-neighbor hopping between electron states produced by In atoms in a metal-like coordination at defective sites of the Ge network.