Spectroscopic Studies of the Electronic Structure of Metal-Semiconductor and Vacuum-Semiconductor Interfaces

The electronic structure and properties of semiconductor interfaces including both vacuum-semiconductor and metal-semiconductor interfaces as well as relevant metal and semiconductor materials have been investigated under this contract. The emphasis has been on elucidating the electronic properties of these materials and their interfaces, e.g., metal-semiconductor Schottky barriers, which are of far reaching importance in such semiconductor devices as MOSFETS, CCD devices, photovoltaic devices, etc. Extensive studies of the electronic structure of semiconductor surfaces and interfaces and related metal surfaces have been performed as a function of surface preparation (include laser annealing), doping, thickness of adsorbed overlayers, etc. The principle technique used has been photoelectron spectroscopy (XPS and UPS - with an emphasis on angle-resolved studies using synchrotron radiation and yield spectroscopy); other techniques include electron energy loss spectroscopy, low energy electron diffraction and theoretical band structure methods. Major achievements of our research program includes world-leading contributions to: (1) the electronic structure of cleaned and annealed Si(111) surfaces; (2) accurate experimental determinations of electron energy vs momentum band dispersions E(k) of selected materials (such E(K) dispersions are of central importance in solid state physics in understanding the electronic, physical and chemical properties of materials); and (3) the development and application of surface core level spectroscopy, a promising new photoemission technique.