PN Junction Biasing Quiz

Study Notes

Forward bias in a PN junction allows current flow from p to n, while reverse bias prevents current flow, with only a tiny current due to minority charge carriers.
Understanding the mechanism of charge flow in forward and reverse bias is crucial for understanding transistors.
In forward bias, at around 0.7 volts, a heavy current flows as holes migrate to the n-region and electrons migrate to the p-region due to diffusion, not being pushed by the battery.
The electric field in the depletion region before attaching the battery acts as a barrier, with diffusion being the driving force of holes and electrons movement.
Recombination ensures that diffusion never stops by preventing equalization of hole concentrations, allowing current to flow continuously.
Recombination is crucial for the forward current, sometimes referred to as the recombination current in textbooks.
In forward bias, holes reaching the end region recombine with electrons, creating a flow of electrons in the external wire and maintaining current flow.
Reverse bias widens the depletion region, almost stopping diffusion, but minority charge carriers can create a tiny current due to acceleration by the electric field.
The reverse current is independent of voltage, as it is driven by thermal generation of charge carriers in the depletion region, not by the strength of the electric field.
Increasing voltage in reverse bias does not increase current, as current is determined by the number of charge carriers generated per second, not by the speed of carrier movement.
The reverse current is often referred to as the generation current due to its dependence on carrier generation rather than voltage.