Active solid-state devices (e.g. – transistors – solid-state diode – Heterojunction device – Bipolar transistor
Patent
1992-04-30
1995-09-05
Crane, Sara W.
Active solid-state devices (e.g., transistors, solid-state diode
Heterojunction device
Bipolar transistor
257592, 257 26, H01L 29161, H01L 29205, H01L 29225
Patent
active
054480876
ABSTRACT:
A heterojunction bipolar transistor with an exponentially graded base doping is disclosed, in addition to a technique for fabricating the transistor. In accordance with the preferred embodiment, the transistor employs a base with an exponentially graded Beryllium doping which varies from 5.times.10.sup.19 cm.sup.-3 at the base-emitter junction to 5.times.10.sup.18 cm.sup.-3 at the base-collector junction. The built-in field due to the exponentially graded doping profile significantly reduces base transit time despite bandgap narrowing associated with high base doping. Compared to devices with the same base thickness and uniform base doping, the cut off frequency is increased and the maximum frequency of oscillation is also increased. Also, consistently higher common emitter current gain results even though the Gummel number is twice as high and the base resistance is reduced by 40%.
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Streit et al, `Effect on Exponentially Graded Base . . . ` IEEE Electron Device Letters, vol. 12 H5, May 1991, pp. 194-196.
Liem Tran, et al.; "In AlAs/InGaAs HBT with Exponentially Graded Base Doping and Graded in GaALAs Emitter-Base Junction"; Fourth International Conference on Indium Phosphide and Related Materials; Cat. No. 92CH3104-7 pp. 438-441 (Apr. 1992).
Streit, D. C.; "High Performance HBT's with Built-in Base Fields Exponentially-Graded Doping vs. Graded Composition" In Proceeding IEEE/Cornell Conference on Advanced Concepts in High Speed Semiconductor Devices and Circuits; Cat. No. 91CH3092-4; pp. 325-333 (Aug. 1991).
Oki Aaron K.
Streit Swight C.
Crane Sara W.
Meier Stephen D.
TRW Inc.
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