Modulating HBT's current gain by using externally biased on-ledge Schottkydiode

The current gain of heterojunction bipolar transistors (HBT's) can be effec tively modulated through Schottky diodes that contact the emitter passivati on ledge directly. The behavior of the gain modulation is determined by the degree of the emitter ledge depletion. If the ledge is fully depleted, HBT 's current gain can be modulated in the whole base-emitter bias voltage (V- BE) range up to 1.6 V, If the ledge is partially depleted, HBT's current ga in can be modulated only in the low V-BE range (<1.35 V). This discovery le ads to a simple method for monitoring the effectiveness of HBT's emitter le dge passivation and offers new insights to the mechanism of HBT gain degrad ation. It also creates a four-terminal HBT with an extra ledge electrode bi ased to control and modulate device's current gain at microwave frequencies .