Interface and surface science have been important in the development of semicon­ ductor physics right from the beginning on. Modern device concepts are not only based on p-n junctions, which are interfaces between regions containing different types of dopants, but take advantage of the electronic properties of semiconductor­ insulator interfaces, heterojunctions between distinct semiconductors, and metal­ semiconductor contacts. The latter ones stood almost at the very beginning of semi­ conductor physics at the end of the last century. The rectifying properties of metal-semiconductor contacts were first described by Braun in 1874. A physically correct explanation of unilateral conduction, as this deviation from Ohm's law was called, could not be given at that time. A prerequisite was Wilson's quantum theory of electronic semi-conductors which he published in 1931. A few years later, in 1938, Schottky finally explained the rectification at metal-semiconductor contacts by a space-

1. Preliminary Remarks.- 2. Conceptual Models.- 3. Computational Results.- 4. Experimental Data.- 5. Surface-Science Approach to Schottky Contacts.- 6. Concluding Remarks.- References:.- Reprinted Articles.- Additional Reference.- Reprinted Articles.- Ueber die Stromleitung durch Schwefelmetalle, Pogg. Ann. (1874).- Zum Mechanismus der Richtwirkung in Kupferoxydulgleichrichtern, Physik. Z. (1929).- Halbleitertheorie der Sperrschicht, Naturwissenschaften (1938).- Note on the Contact between a Metal and an Insulator or Semiconductor, Proc. Camb. Phil. Soc. (1938).- Abweichungen vom Ohmschen Gesetz in Halbleitern, Physik. Z. (1940).- Surface States and Rectification at a Metal Semiconductor Contact, Phys. Rev. (1947).- Surface States and Barrier Height of Metal Semiconductor Systems, J. Appl. Phys. (1965).- Theory of Surface States, Phys. Rev. (1965).- Fundamental Transition in the Electronic Nature of Solids, Phys. Rev. Lett. (1969).- Density of States and Barrier Height of Metal-Si Contacts, J. Phys. C: Solid State Physics (1971).- Metal-semiconductor Junctions for (110) Surfaces of Zinc-blende Compunds, Phys. Rev. B (1976).- Electronic Structure of a Metal Semiconductor Interface, Phys. Rev. B (1976).- Ionicity and the Theory of Schottky Barriers, Phys. Rev. B (1977).- Chemical Trends in Metal-semiconductor Barrier Heights, Phys. Rev. B (1978).- Transition in Schottky Barrier Formation with Chemical Reactivity, Phys. Rev. Lett. (1978).- New and Unified Model for Schottky Barrier and III-V Insulator Interface States Formation, J. Vac. Sci. Technol. (1979).- Schottky Barriers: An Effective Work Function Model, AppL Phys. Lett. (1981).- The Foramtion of the Schottky Barrier at the V/Si Interface, J. Vac. Sci. Technol. (1982).- Formation of Ultrathin Single- Crystal Silicide Films on Si: Surface and Interfacial Stabilization of Si-NiSi2Epitaxial Strucutures, Phys. Rev. Lett. (1983).- Schottky Barrier Heights and the Continuum of Gap States, Phys. Rev. Lett. (1984).- Schottky Barrier Formation at Single-Crystal Metal Semiconductor Interfaces, Phys. Rev. Lett. (1984).- Reflection High-energy Electron Diffraction Study of the Growth of In on GaAs (110) at Different Temperatures, J. Vac. Sci. Tecnol. B (1986).- Direct Variation of Metal-GaAs Schottky Barrier Height by the Influence of Interface S, Se and Te, AppL Phys. Lett. (1985).- Interface Potential Changes and Scottky Barriers, Phys. Rev. B (1985).- Ruthenium-Induced Surface Staes of n-GaAs Surfaces, J. Vac. Sci. Technol. B. (1986).- Metallization and Scottky Barrier Formation, Phys. Rev. B (1986).- On the Present Understanding of Schottky Contacts , Festkörperprobleme (1986).- Role of Virtual Gap States and Defects in Metal Semiconductor Contacts Phys. Rev. Lett. (1987).- Initial Stages of Schottky Barrier Formation: Temperature Effects, J. Vac. Sci. Technol. B (1987).- Kinetics Study of Initial Stage Band Bending at Metal GaAs (110) Interfaces, J. Vac. Sci. Technol. B (1987).- The Schottky Contact in a Xe/Metal Interface Probed by Inverse Photoemission, Europhys. Lett. (1987).- Origin of the Excess Capacitance at Intimate Schottky Contacts, Phys. Rev. Lett. (1988).- Correlation between EfPinning and Development Metallic Character in Ag Overlayers on GaAs (110), Phys. Rev. Lett. (1988).- Direct Investigation of Subsurface Interface Electronic Structure by Ballistic-Electron-Emission Microscopy, Phys. Rev. Lett. (1988).- Chemical Trends in Schottky Barriers: Charge Transfer into Adsorbate Induced Gap States and Defects, Phys. Rev. B (1988).- The Advanced Unified Defect Model forSchottky Barrier Formation, J. Vac. Sci. Technol. B (1988).- Screening and Derealization Effects in Schottky Barrier Formation, J. Vac. Sci. Technol. B (1988).- Tight-Binding Model of Surface Donor-States Induced by Metal Adatoms on GaAs (110) Surfaces, Europhys. Lett. (1988).- Switching of Band Bending at the Nonreactive CsOx/GaAs (110) Interface, Phys. Rev. Lett. (1989).- Metallicity and Gap States in Tunneling to Fe Clusters on GaAs (110), Phys. Rev. Lett. (1989).