The use of base ballasting to prevent the collapse of current gain in AlGaAs/GaAs heterojunction bipolar transistors

We propose the use of base-ballasting resistance to guarantee absolute thermal stability in AlGaAs/GaAs heterojunction bipolar transistors (HBTs). Base-ballasted HBTs are fabricated and the measured I-V, regression and S-factor characteristics are discussed. We present a numerical model which elucidates the reasons why the base-ballasting scheme is helpful to HBTs but is damaging to silicon bipolar transistors. We compare measured small-signal and large-signal performances of unballasted, emitter-ballasted, and base-ballasted HBTs.