Effect of junction and band-gap grading on the electrical performance of molecular beam epitaxial grown AlGaAs/GaAs/AlGaAs double-heterojunction bipolar transistors

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Abstract
Current-voltage characteristics of AlGaAs/GaAs/AlGaAs double-heterojunction bipolar transistors (DHBTs) grown by molecular beam epitaxy have been studied. DHBTs with both abrupt and graded heterojunctions at the emitter-base and base-collector heterojunctions have been employed for the study. It is noted that DHBTs with abrupt heterojunctions are better than those with graded heterojunctions. These abrupt heterojunctions, along with a nonuniform doping in the base, lead to significantly improved results in current gain and offset voltage. Physical reasons underlying the improvement in the current gain and offset voltage have been analyzed.