Structural, optical, and electrical studies of amorphous hydrogenated germanium

High-density, non-porous, highly photoconductive films of amorphous hydrogenated germanium (a-Ge:H) showing minimal microstructure were prepared using the r.f. glow discharge method out of a gas plasma of GeH₄ and H₂. These films, deposited onto substrates mounted on the powered electrode of a diode reactor, showed remarkable improvement over codeposited material taken from the unpowered electrode. Films were also prepared under the systematic variation of substrate temperature, discharge power, and dilution of the plasma by H₂. For the reactor geometry used, dilution of the plasma is found to be essential to the preparation of high-quality a-Ge:H. The conditions for the preparation of optimized a-Ge:H material were quite different from those found to produce optimized a-Si:H in this reactor. We assert this to be the principal cause of the finding of inferior properties for a-SiGe:H alloys when compared with a-Si:H.