Dielectrics on semiconductors

Current issues related to the physics and technology of dielectrics on semiconductors are discussed. Fluorides offer new possibilities for epitaxial, three-dimensional structures, e.g. buffer layers to couple III-V and II-VI devices to silicon technology and stacked silicon devices. A key to the systematic development of new materials is a microscopic understanding of the structure and bonding at the dielectric/semiconductor interface. Our current knowledge is illustrated by recent results for SiO2/Si(100) and CaF2/Si(111) interfaces. Several issues need to be resolved for device applications. The reverse epitaxy of semiconductors (or metals) on insulators is found to be much more difficult than epitaxy of dielectrics on semiconductors. As the culprit one can identify the large difference in surface energies which prevents smooth layer-by-layer growth. A second problem is the reduction of defect densities for epitaxial interfaces. Surface techniques are shown to be helpful in understanding the microscopic origin of these problems and in devising solutions in a systematic way.