Suppression of emitter size effect on the current-voltage characteristics of AlGaAs/GaAs heterojunction bipolar transistors

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Abstract
The effect of emitter periphery‐to‐area ratio on the current‐voltage characteristics of Npn AlGaAs/GaAs heterojunction bipolar transistors has been studied. It is shown that an electric field generated by a properly controlled nonuniform doping of the base region can very significantly suppress the reduction in current gain when the emitter area‐to‐periphery ratio is decreased, as is the case in high‐speed devices. The superiority of doping‐induced grading to compositional grading is discussed.