Current Gain Rolloff in Graded-Base SiGe Heterojunction Bipolar Transistors

Emmanuel F. Crabbé, John D. Cressler, Gary L. Patton, Johannes M.C. Stork, James H. Comfort, Jack Y.C. Sun

Research output: Contribution to journalArticlepeer-review

32 Scopus citations


We report the experimental observation of a novel effect in SiGe heterojunction bipolar transistors (HBT's) with graded bases which results in a significant emitter-base bias dependence of the current gain. The nonideal collector current is caused by the interaction of the bias dependence of the emitter-base space-charge region width and the exponential dependence of the collector current on the germanium concentration at the edge of the space-charge region. The resulting current gain rolloff must be taken into account for accurate modeling of bipolar transistors with bandgap grading in the base.

Original languageEnglish
Pages (from-to)193-195
Number of pages3
JournalIEEE Electron Device Letters
Issue number4
StatePublished - Apr 1993

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