Gallium arsenide varactor diodes

From consideration of the factors influencing the design of varactor diodes for use in high-frequency parametric amplifiers and multipliers it appears that GaAs is the most suitable choice of semiconductor. The high carrier mobility of this material over a wide range of temperatures should enable high cut-off frequency varactor diodes tobe fabricated which will operate at the low temperatures required for ultra-low-noise parametric amplification. In addition, the high cut-off frequency should provide efficient harmonic generation at the higher microwave frequencies. An appraisal of the performance of an initial GaAs diode indicated that low frequency measurements were unreliable, and this has led to the development of a microwave measurement technique which has proved to be an extremely useful method of evaluating the junction parameters. As a result of these measurements new device structures have been evolved which reduce the microwave losses and simplify the fabrication processes. Three forms of diode have been developed for use at C, X and Q-band having cut-off frequencies of 150, 250 and 700 Gc/s (at zero bias) respectively, and the construction and performance of these varactors are described.