A high-current-gain, high-speed P-n-p AlGaAs/InGaAs/GaAs collector-up heterojunction bipolar transistor

Abstract
A Pnp AlGaAs/InGaAs/GaAs collector‐up heterojunction bipolar transistor (C‐up HBT), grown by three‐stage molecular beam epitaxy, has been fabricated, and its dc and high‐frequency performances have been evaluated. The use of a graded InxGa1−xAs (x=0.0–0.09) is shown to improve the common‐emitter current gain (β) and to greatly reduce the base transit time (τb) for the Pnp C‐up HBTs. A maximum current gain (β) of 150 was measured for a 16×17 μm2 device. From S‐parameter measurements, a best unity‐gain cutoff frequency fT=43 GHz at a collector current of −10 mA was achieved using a 5×10 μm2 collector area. The results show that the Pnp C‐up HBTs may be useful for future planar integrated circuit applications.

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