Results on the optical absorption, photoluminescence, and photoconductivity spectra and on electrical-transport data of amorphous ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$:H alloys prepared from the plasma decomposition of silane and germane are presented. An attempt is made to find a self-consistent interpretation of the data in terms of changes in the optical energy gap and in the gap-state densities with mixtures of different ratios of Si${\mathrm{H}}_4$ to Ge${\mathrm{H}}_4$. It is found that the photoconductivity and the photoluminescence intensity are much higher than would be expected from the previously deduced values of the ratio of Si—H to Ge—H bonds from infrared absorption spectra. The principal conclusion of our results is that the changes in the intrinsic properties of a random tetrahedrally coordinated alloy as a function of alloy composition $x$ are often masked by the extrinsic effects of changes with $x$ in H content, defect density, and microstructure; the latter changes depend sensitively on the preparation method.

• Received 4 December 1981

DOI:https://doi.org/10.1103/PhysRevB.25.7678