# Homework Help: Resistance of semiconductor

1. Oct 20, 2009

### songoku

1. The problem statement, all variables and given/known data
The resistance of a semiconductor decreases rapidly with increasing temperature. The main factor contributing to this effect is the rapid increase, with increasing temperature, of

a. the speed of the random motion of the free charge carriers
b. the concentration of the free charge carriers
c. the drift velocituy of the free charge carriers
d. the frequency of vibration of the atoms of the semiconductor
e. the amplitude of vibration of the atoms of the semiconductor

2. Relevant equations

3. The attempt at a solution
I read a little about semiconductor on wiki. I think the answer is (c). Am I right?

Thanks

2. Oct 20, 2009

### Mapes

3. Oct 21, 2009

### songoku

Hi Mapes

Ups sorry, I mean the answer is (b). This is part of the article I read :

"In extrinsic (doped) semiconductors, dopant atoms increase the majority charge carrier concentration by donating electrons to the conduction band or accepting holes in the valence band. For both types of donor or acceptor atoms, increasing the dopant density leads to a reduction in the resistance."

So based on that, I think the answer is (b). But I don't know the reason why....

Thanks

4. Oct 21, 2009

### Mapes

OK, I agree with this answer, but I'd keep looking for the reason why! Why would temperature change the charge carrier concentration?

5. Oct 21, 2009

I think the increase is much greater with intrinsic(pure) semiconductors so I would advise you to do a little research on these.The answer comes most easily from the equation linking current with charge density, electron charge,drift velocity and conductor cross sectional area.Try a little search and come back if you cant find the equation.

6. Oct 27, 2009