Single-crystal films of silicon on insulators

The preparation and properties of single-crystal films of silicon on insulating substrates are reviewed. Attempts have been made to prepare single-crystal films by epitaxial deposition on insulating substrates such as Al2O3, SiO2, MgAl2O4, SiC and BeO, and to a lesser extent by recrystallization and controlled-nucleation experiments on amorphous substrates. Evaporation, sublimation, sputtering, vapour-liquid-solid processes, and vapour techniques, including silane, silicon tetrachloride and other silicon halides, have been used to deposit silicon films. The differences between these processes and the factors affecting the perfection of films are discussed. A good deal of research has been devoted to silicon films on single-crystal sapphire substrates. Although diode, field-effect and bipolar devices have been fabricated the perfection of the films is still inadequate for some purposes. Factors affecting the perfection include interaction of the substrate and film during deposition, the perfection of the substrate surface, the nucleation and growth processes, and the presence of impurities and stresses in the film. Particular attention is paid to the orientation relationships between the silicon and the sapphire.