# Drift current of a PN junction

1. May 8, 2015

### get-physical

The magnitude of a drift current density is given by J = qnv, where q is the carrier charge, n is the carrier density per unit volume, and v is the carrier drift velocity. q is a physical constant and n is independent of bias. But when an external electric field is applied, the minority charge carriers must surely accelerate and change their drift velocity. How is the drift current of a pn junction not a function of bias?

2. May 9, 2015

### boshua

The drift current of a pn junction is dependent upon the bias placed across the junction. The drift velocity v is dependant upon the mobility of the holes and electrons in the junction as well as the electric field placed across the junction.

3. May 9, 2015

### FOIWATER

The equation for drift current that I learned was Jdrift=sigma*electric field where sigma is the (q*n*mobility)

It is as far as I know a function of the electric field as well maybe re check the equation

4. May 10, 2015

### get-physical

There are two mechanisms of conduction in a semiconductor: diffusion and drift. Diffusion current, on one hand, is clearly affected by changes in bias because the number of majority carriers that are able to diffuse across the junction varies exponentially according to the Maxwell-Boltzmann distribution. On the other hand, minority carriers do not face a potential barrier so their number is unaffected by changes in bias and that is the crux of the explanation as to why, according to every reputable source I've come across, the drift current of a PN junction is independent of bias. But the fact that minority carriers accelerate and change their drift velocity in the presence of an applied electric field is never accounted for. Why?