Hall Effects Theory

[tOngEh]

I have done a lab sesion on hall effect. There a few points that still doubted me.
1)Why are holes considered positive charges?
2)The effects of spread in carriers velociity are assumed negligible in my lab session, how will it affect my Hall coefficient if they are not negligible.

It will be good for me to close this chapter with maximum understanding.

Jason

[Pythagorean]

Q1)

If you consider a material made of atoms, it is, in general, neutral. Each atom of the material has the same number of electrons as it does protons.

If you pull an electron away from one of the atoms, the atom now has a net positive charge. The proton is generally fixed to the nucleus of the material, which doesn't move appreciably through the material. As you probably know, it's the electrons that move.

So when you dope a semiconducting material with an acceptor, you pull an electron off the previously neutral material, leaving a "hole" behind. That is, the core atom that was neutral lost an electron.

This wiki illustrates the process of doping simply:
http://en.wikipedia.org/wiki/Acceptor_%28semiconductors%29