Diffused epitaxial GaAlAs‐GaAs heterojunction bipolar transistor for high‐frequency operation

A GaAlAs‐GaAs heterojunction bipolar transistor (HBT) has been realized by liquid phase epitaxy with a very low emitter doping. A diffused epitaxial structure has been developed. Transition frequencies close to 5 GHz for IC = 10 mA have been measured, and high transition frequency has been obtained at low current ( fT = 1.3 GHz for IC = 1 mA) in spite of a rather large emitter base area (SEB∼4.10−5 cm2). These figures are the best reported so far for HBT’s and are very promising for low‐power high‐speed logic.