Highhyphen;gain, highhyphen;frequency AlGaAs/GaAs graded bandhyphen;gap base bipolar transistors with a Be diffusion setback layer in the base

摘要

AlGaAs/GaAs heterojunction bipolar transistors (HBTrsquo;s) with graded bandhyphen;gap bases were fabricated from computerhyphen;controlled molecular beam epitaxy layers. It was found that the use of an undoped setback layer of 200ndash;500 Aring; 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 mgr;m were obtained which are the highest yet reported for graded base HBTrsquo;s. Zn diffusion was used to contact the base and provides a low base contact resistance. Microwaveshyphen;parameter measurements yieldedfT=5 GHz andfmax=2.5 GHz. Large signal pulse measurements resulted in rise times of tgr;rsim;150 ps and pulsed collector currents ofIc100 mA which is useful for high current laser drivers.