Millimeter-wave point-contact and junction diodes

Millimeter-wave "point-contact" diodes are classed as conventional point-contact diodes (and modifications on them), which depend primarily upon a point-contact metal-semiconductor junction for their rectification properties; or as junction diodes with point-contact geometry, which are small-area millimeter-wave adaptations of the p-n junction diodes, normally made for use at lower frequencies by alloying, diffusion and other techniques. In a general way, techniques used in the fabrication of these various diodes are described; then the uses to which they have been put is detailed, and the best reported performance characteristics in various millimeter-wave applications are compared. Emphasis is put on demonstrated performance, but highly experimental and tentative laboratory results are freely quoted. Included are discussions of 1) conventional point-contact diodes of various semiconductors; 2) diodes having point-contact geometry but exhibiting electrical properties approximating those of alloyed and diffused p-n junctions, diodes made by planar techniques, a "thermoelectric effect hot carrier" diode, point-contact photodetectors and photoemitters; and 3) a millimeter-wave avalanche transit-time oscillator diode. The use of these diodes as millimeter-wave detectors, amplifiers, oscillators, harmonic generators, and modulators is considered.