AlGaAs/Ge/GaAs heterojunction bipolar transistors grown by molecular beam epitaxy

An N-Al/sub 0.22/Ga/sub 0.78/As emitter, p-Ge base, and n-GaAs collector (AlGaAs/Ge/GaAs) heterojunction bipolar transistor (HBT) in the emitter-up configuration grown by molecular beam epitaxy is discussed. Devices exhibited common-emitter current gains of as high as 300 at a collector current density of 2000 A/cm/sup 2/ and a collector voltage of 4 V. As the device area is reduced from 50*50 to 10*40 mu m, the current gain did not show significant changes, suggesting a low surface recombination velocity in the Ge base.<
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