The Physics of the Transistor Jim Royston Electronic Engineering La Trobe University

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.

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

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 ≈ β 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.

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

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).