Abstract :
A new type of heterojunction bipolar transistor, designated the BICFET, (for Bipolar Inversion Channel Field Effect Transistor), is proposed. Unlike the conventional heterojunction bipolar transistor (HBT), the BICFET does not have a base. Instead, it relies on a field effect action to induce and modulate an inversion channel (which replaces the base) at the interface between the wide- and narrow- bandgap materials, to control current flow in the system. The BICFET has the high current gain associated with HBTs. However, since the BICFET does not have a base layer, it does not experience the deleterious base layer effects, such as charge storage, recombination, base transit time, etc. In particular, it has a much lower input capacitance and the capability of much higher current drive than a HBT, the combination of which augurs well for very high speed operation. In addition to the basic theory, common-emitter (CE) output and input characteristics are generated for two practical systems, and a possible integrated structure is indicated. A small-signal CE model for the device is also presented. The model predicts h cut-off frequencies as high as 10,000 GHz; however, in practice, collector transit time effects will reduce the cut-off frequency to about 600 GHz.
