ABSTRACT
Single-heterojunction bipolar transistors (SHBT) have been studied widely for high performance circuit applications and it is well established that the offset voltage in these devices can be attributed to the difference in turn-on voltages of the emitter and collector junctions. In this chapter, the authors report a novel 2-DEG emitter HBT which has a low offset voltage and high gain. The large valence band offset at the AlGaAs/GaAs heterojunction allows a lightly doped emitter to be used without significantly degrading the emitter injection efficiency. However, a large conduction band discontinuity is also present which causes the formation of a potential spike in the emitter-base space charge region. The 2-DEG emitter device structure provides a simple and practical way to achieve an emitter with homojunction characteristics while maintaining the blocking of back injected minority carriers. The high gain and low offset voltage make this device an attractive candidate for high speed circuit applications.
