Drift current of a PN junction

In summary, the drift current of a pn junction is determined by the bias placed across the junction, as the drift velocity of minority carriers is affected by the electric field. However, the drift current is not affected by changes in bias due to the fact that minority carriers do not face a potential barrier. This is due to the two mechanisms of conduction in a semiconductor: diffusion and drift. While diffusion current is affected by changes in bias, the number of minority carriers is unaffected, leading to a constant drift current.
  • #1
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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?
 
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  • #2
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
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
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?
 

1. What is drift current in a PN junction?

Drift current in a PN junction is the flow of charge carriers (electrons and holes) due to the influence of an electric field. This electric field is created by the difference in the concentration of dopants (impurities) within the P and N regions of the junction.

2. How is drift current different from diffusion current?

Diffusion current is the flow of charge carriers from an area of high concentration to an area of low concentration. It is caused by the random thermal motion of particles. On the other hand, drift current is caused by the electric field and is not dependent on concentration gradients.

3. What factors affect the magnitude of drift current in a PN junction?

The magnitude of drift current is affected by the strength of the electric field, the concentration of dopants, and the mobility of the charge carriers in the material. A higher electric field or higher dopant concentration will result in a higher drift current, while a lower mobility will decrease the drift current.

4. How does drift current influence the behavior of a PN junction diode?

In a PN junction diode, drift current is responsible for creating the depletion region (a region with very few mobile charge carriers) which acts as a barrier to the flow of current. As the electric field increases, the width of the depletion region also increases, and this affects the overall behavior of the diode.

5. Can drift current be controlled in a PN junction?

Yes, the magnitude of drift current can be controlled by varying the applied voltage across the PN junction. By changing the voltage, the strength of the electric field can be altered, which in turn affects the drift current. This allows for the manipulation of the diode's behavior and is an important aspect of semiconductor device design.

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