Suppression of Emitter Size Effect on Current Gain in AlGaAs/GaAs HBTs

The dependence of current gain on emitter size is investigated for the case of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with graded base structure. No emitter-size effect on current gain is observed in the high collector current density region employed in practical operation. Graded base structures are demonstrated to be useful in scaling down of transistor size to attain high speed HBTs.