Microwave Schottky Barrier Diodes

Abstract

Point contact diodes have been in use for many decades for mixer and detector application from uhf through millimeter-wave frequencies. The first published paper on the subject appeared in 1874 when Braun reported the asymmetrical nature of conduction between metal points and crystals. Point contacts are relatively unsophisticated devices consisting of a metal whisker making pressure contact with the semiconductor chip, normally tungsten for silicon and phosphorus bronze for germanium and gallium arsenide. The point contact diodes are generally encapsulated in axial lead glass, axial prong ceramic, cartridge-type ceramic (1N21 and IN23), or metal coaxial enclosures. In the early 1960s Schottky barrier diodes were introduced for similar applications. The Schottky diode, also a metal-semiconductor rectifying junction, is formed by depositing a variety of metals on n-type or p-type semiconductor materials by chemical deposition (electroplating), evaporation or sputtering; n-type silicon and n-type gallium arsenide (GaAs) are the most commonly used materials. Owing to the need for higher cutoff frequency, GaAs devices are preferred at millimeter-wave frequencies, since electrons have a higher mobility in GaAs than in silicon.