High-gain, high-frequency AlGaAs/GaAs graded band-gap base bipolar transistors with a Be diffusion setback layer in the base

R. J. Malik, F. Capasso, R. A. Stall, R. A. Kiehl, R. W. Ryan, R. Wunder, C. G. Bethea

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27 Scopus citations


AlGaAs/GaAs heterojunction bipolar transistors (HBT's) with graded band-gap bases were fabricated from computer-controlled molecular beam epitaxy layers. It was found that the use of an undoped setback layer of 200-500 Å to offset Be diffusion in the emitter resulted in significant current gain increases. Maximum current gains of 1150 for a base width of 0.18 μm were obtained which are the highest yet reported for graded base HBT's. Zn diffusion was used to contact the base and provides a low base contact resistance. Microwave s-parameter measurements yielded fT=5 GHz and f max=2.5 GHz. Large signal pulse measurements resulted in rise times of τr∼150 ps and pulsed collector currents of I c>100 mA which is useful for high current laser drivers.

Original languageEnglish (US)
Pages (from-to)600-602
Number of pages3
JournalApplied Physics Letters
Issue number6
StatePublished - Dec 1 1985


ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)

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