Analytical modeling of current gain-Earth voltage products in Si/Si1-xGex/Si heterojunction bipolar transistors

Erwin J. Prinz, James C. Sturm

Research output: Chapter in Book/Report/Conference proceedingConference contribution

25 Scopus citations


The tradeoff between common emitter current gain beta and Early voltage VA in heterojunction bipolar transistors (HBTs), where both bandgap and doping can vary in the base, has been studied. The Early voltage depends exponentially on the difference between the bandgap at the collector side of the base and the largest bandgap in the base, allowing very high Early voltages with only very thin narrow bandgap regions. Using Si/Si1-xGex/Si narrow gap base HBTs with a two layer stepped base, beta VA products of over 100000 V have been achieved for devices with a base width of only 400 AA. However, the presence of parasitic potential barriers for minority carriers at the base-collector junction of a HBT degrades VA because changing the base-collector voltage affects not only the width but also the height of these barriers. They can be caused, e.g., by base dopant outdiffusion into the collector due to high-temperature processing. An analytical model of the effect of such barriers on the Early voltage is presented.

Original languageEnglish (US)
Title of host publicationInternational Electron Devices Meeting 1991, IEDM 1991
PublisherInstitute of Electrical and Electronics Engineers Inc.
Number of pages4
ISBN (Electronic)0780302435
StatePublished - 1991
EventInternational Electron Devices Meeting, IEDM 1991 - Washington, United States
Duration: Dec 8 1991Dec 11 1991

Publication series

NameTechnical Digest - International Electron Devices Meeting, IEDM
ISSN (Print)0163-1918


OtherInternational Electron Devices Meeting, IEDM 1991
Country/TerritoryUnited States

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Materials Chemistry
  • Electrical and Electronic Engineering


  • Analytical models
  • Bipolar transistors
  • Capacitance
  • Degradation
  • Digital circuits
  • Doping profiles
  • Heterojunction bipolar transistors
  • Photonic band gap
  • Temperature
  • Voltage


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