AlGaAs/GaAs Heterojunction Bipolar Transistors For Power Applications

Abstract

Heterojunction bipolar transistors (HBT) are one of the most promising modern devices for the needs of present microwave and millimeter wave systems. Not only do HBTs offer high frequency operation capability [l-31 but a l s o they have the potential for several fold increase in power and packing density coimpared to FETs[4]. The superior performance of HBTs at high frequencies over conventional Si homojunction bipolar transistors originate from the use of a heterojunction at the emitter-base interface. In this way, the device can produce current gains even when the base layer is substantially higher doped than the emitter. Resulting low base resistance and smaller emitter charging time constant improves high frequency operation of the transistor. The use of GaAs with its higher electron mobility and semiinsulating (SI) substrate properties further enhances this performance.