# Difution drift currect question

1. May 21, 2010

### nhrock3

$$J_e=q\mu \bar{n}E-qD_e\frac{d\bar{n}}{dx}$$
i cant understand this equation
what each member of this equation

i only know that $$\mu$$ is the drift coefficient
E is the field

what the rest of the memebers represent
?

2. May 21, 2010

### Staff: Mentor

I googled diffusion drift current, and got lots of good hits. Here's one that should answer your question:

.

3. May 22, 2010

### nhrock3

n is the electron density what is the meening of
dn/dx
?

?

the is also a formula for hole current
why it has plus in the middle (in the electron current we have minus in the meedle)
??

4. May 22, 2010

### Spiral13

dn/dx would be the derivative of electron density with respect to the coordinate x. In other words, if you're simply dealing with a semiconductor in which the elctron density only changes in x (i.e. y, and z components are constant), there will be a diffusion current where electrons will diffuse from a higher concentration area to a lower concentration area. This is mathematically depicted by 'dn/dx'.

D_e (or D_n) is the diffusion coefficient of electrons. It depends on the mobility of the electrons, and temperature of the sample.

The hole current has a plus because holes are positively charged as opposed to electrons which are negatively charged

5. May 22, 2010

thanks :)