SI1-XGEX SAPPHIRE STRUCTURE FABRICATED BY MOLECULAR-BEAM EPITAXY

We investigated the annealing behavior and optical characteristics of Si0.8Ge0.2 layers and Si0.8Ge0.2/Si superlattice layers grown on a sap phire substrate for the first time ever by molecular beam epitaxy (MBE ). It is found that the interface between the Si0.8Ge0.2 and the Si la yers is smooth and without defects, and that the crystalline structure is thermally stable even after annealing for 1 h at 850-degrees-C. In both the Si0.8Ge0.2/Si/sapphire structure and the (Si0.8Ge0.2/Si) sup erlattice/Si/sapphire structure, we obtained absorption about five tim es that of Si/sapphire structures with film layers of the same thickne ss for light at a wavelength of 800 nm. Indications are that these str uctures hold great promise as a substrate for thin-film photosensors w ith excellent sensitivity throughout the visible range.