The Physics of the Transistor

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The Physics of the Transistor

• Jim Royston
• Electronic Engineering
• La Trobe University

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• The B-E junction is forward biased and the C-B
  junction is reverse biased.
• There is an exponential relationship between the
  thickness of the B-E depletion region and the
  current of electrons "injected" into the base as
  minority carriers.

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• The base region is very thin and has a lower
  doping than the emitter or collector.
• The profile of concentration of minority carriers
  (electrons in an NPN transistor) in the base is
  linear.
• The amplifying action is produced by transferring
  a current from a low-resistance circuit to a high
  resistance circuit.
• transfer resistor ? transistor

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• The C-B junction has a reverse bias leakage
  current ICBO which is typically microamps or
  nanoamps, and can be neglected unless temperature
  effects are important.
• Approximately, ICEO ß ICBO but both currents
  are small.
• There is an injection of holes into the emitter,
  where they are minority carriers, from the base
  this can be kept small by heavily doping the
  emitter with donor impurities.

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Gray, P. R. Meyer, R. G., "Analysis Design of
Analog Integrated Circuits", 3rd edition 1993,
New York, John Wiley Sons.
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References

• William Beaty "How Do Transistors Work?" 1995
  http//amasci.com/amateur/transis.html
• Wikipedia "Bipolar Junction Transistors" accessed
  2007 http//en.wikipedia.org/wiki/Bjt
• Gray, P. R. Meyer, R. G., "Analysis Design of
  Analog Integrated Circuits", 3rd edition 1993,
  New York, John Wiley Sons.
• Bogart, T. F. et al, "Electronic Devices
  Circuits", 3rd edition 2001, Upper Saddle River,
  New Jersey, Prentice-Hall (Pearson).
• Boylestad, R. L. Nashelsky, L., "Electronic
  Devices and Circuit Theory", 8th edition 2003,
  Upper Saddle River, New Jersey, Prentice-Hall
  (Pearson).