Abstract
This paper contains a review of our recent studies on the medium-range order in glow-discharge-produced a-Ge: H using a combination of differential scanning calorimetry, isothermal calorimetry, gas evolution, and transmission and scanning electron microscopy. Taken together with evidence from Raman and infrared spectroscopy and X-ray diffraction, and evidence of changes in the structural parameters with carefully chosen annealing procedures, these data suggest correlations between deposition, structural and photoelectronic parameters and properties. The data show conclusively that the best material for fundamental and device studies has a high atomic density and a homogenous structure with minimal admixture of low-density tissue to high-density islands. In material prepared under less than optimum conditions, there occurs, to a greater or lesser degree, heterogeneity revealed directly by electron microscopy, and indirectly by structural relaxation at relatively low temperatures and even two stages of crystallization in the two-phase island-and-tissue network. These effects also occur in unhydrogenated Ge and in unhydrogenated and hydrogenated amorphous Si and Si-Ge alloys. Increased heterogeneity in the structure can be correlated unambiguously with a deterioration in the photoelectronic properties.
