Editing Bipolar junction transistor (section)

===== Base-width modulation =====
{{Main|Early effect}}
[[File:Early effect (NPN).svg|frame|Top: NPN base width for low collector–base reverse bias; Bottom: narrower NPN base width for large collector–base reverse bias. Hashed regions are [[Depletion width|depleted regions]].]]

As the collector–base voltage (<math>V_\text{CB} = V_\text{CE} - V_\text{BE}</math>) varies, the collector–base depletion region varies in size. An increase in the collector–base voltage, for example, causes a greater reverse bias across the collector–base junction, increasing the collector–base depletion region width, and decreasing the width of the base. This variation in base width often is called the ''[[Early effect]]'' after its discoverer [[James M. Early]].

Narrowing of the base width has two consequences:
* There is a lesser chance for recombination within the "smaller" base region.
* The charge gradient is increased across the base, and consequently, the current of minority carriers injected across the emitter junction increases.

Both factors increase the collector or "output" current of the transistor in response to an increase in the collector–base voltage.