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 chan ges in the optoelectronic properties of the films. The experimental re sults may be explained in terms of acceptor levels produced by tetrahe drally coordinated In, in a way similar to In doping of c-Ge. The tran sition from n-type conduction of as-deposited samples to p-type conduc tion has been monitored through thermopower measurements. Indium conce ntrations 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 conduct ivity at room temperature having an activation energy of a few meV. Th e effect is explained in terms of nearest-neighbor hopping between ele ctron states produced by In atoms in a metal-like coordination at defe ctive sites of the Ge network.