Solid state microwave devices with small active contact and large

Abstract

This disclosure relates to two-terminal solid state microwave devices, such as transferred electron and avalanche effect devices, comprising a high-conductivity semiconductor substrate formed over at least a part of one major surface with an active layer of semiconductor material, a first contact providing electrical contact with the active layer to define the active region of the device, and a second contact on the same side of the substrate, providing a relatively low impedance contact to the substrate in operation of the device at the operating bias current for the active region. To simplify fabrication, both contacts may have substantially identical structures with the second contact also overlying the active layer. In the case of transferred electron devices, the area of the second contact is then made greater than the first so that it is biased below threshold at the operating bias current for the active region; while in the case of avalanche effect devices having rectifying semiconductor junction contacts, only the first contact is reverse biased in operation, the second contact being forward biased to behave as a low resistance contact to the substrate. Methods of fabricating such devices are also disclosed.