Transit-Time Oscillations in BARITT Diodes

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Abstract
A new mechanism of microwave power generation, obtained in metal‐semiconductor‐metal structures with significantly lower noise than Impatt diodes is described. The two metal contacts to the semiconductor form a ``double Schottky barrier'' diode. Carriers are thermionically injected over the forward‐biased barrier and drift through the depleted semiconductor to be collected by the reverse‐biased barrier. When the transit time of the carriers is roughly three‐quarters of the desired microwave period, the structure is shown to have a small‐signal microwave negative resistance. Combining the ideas of thermionic injection over a barrier and transit time, we suggest the acronym BARITT (BARrier Injection Transit Time) for the device. The small‐signal impedance and noise measure of the device are calculated using several approximations to the actual space‐charge distribution and transport properties of this device. A minimum negative Q of about 21 and noise measures significantly less than that of Impatt diodes are predicted. Initial experimental observations of microwave oscillations are given, and reasonable agreement with theory is obtained. In general, the theory predicts well the magnitude of the small‐signal negative resistance with a somewhat smaller bandwidth than observed. The experimental small‐signal amplifier noise measure of 15 dB is verified with practical values as low as 8 dB predicted.

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