THE CUTOFF FREQUENCY OF BASE-GRADED AND JUNCTION-GRADED ALXGA1-XAS DHBTS

TitleTHE CUTOFF FREQUENCY OF BASE-GRADED AND JUNCTION-GRADED ALXGA1-XAS DHBTS
Publication TypeJournal Article
Year of Publication1991
AuthorsANG, O. S., and D. L. Pulfrey
JournalSolid -State Electronics
Volume34
Pagination1325-1328
Date PublishedDEC
Type of ArticleArticle
ISSN0038-1101
Abstract

A detailed model of AlxGa1-xAs double-heterojunction bipolar transistors is used to examine the effects on the cut-off frequency of varying both the degree of base grading in abrupt-junction devices, and the amount of base-collector junction grading in uniform-base devices. It is shown that, in the graded-base case, there is an optimum degree of base grading, stemming from the trade-off between the strength of the aiding field for minority carrier transport across the base and the height of the barrier at the base-collector junction, which inhibits charge flow to the collector. In the uniform-base case, it is shown that a small amount of base-collector junction grading is sufficient to effectively remove the blocking action of the conduction band discontinuity, and so allow the base transit time to attain its diffusion-limited value.

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