# Mobility of holes and electrons

1. May 15, 2008

### jablonsky27

hi,
holes are the absence of electrons in the lattice, right? then how come we say holes have a +ve charge? shouldnt it be zero?
also, why is the mobility of electrons more than holes?
thanks

2. May 15, 2008

### Defennder

This is what I wrote for another thread:

As for the other question, I'm guessing it's something to do with the magnitude of their effective masses.

3. May 15, 2008

### jablonsky27

i should ve searched for that before posting a new thread. it makes sense, yes..

what would the effective mass of a hole be??

4. May 15, 2008

### maverick280857

Where would you usually find a hole? And where would you usually find an electron?

Where == which band?

Yes, the effective masses of holes and electrons are different. The mobility is a function of the effective mass, which is a theoretical tool brought in to simplify the description of a charged particle in a crystal. Classically, the concept of an effective mass is analogous to that of a 'psuedo force' in Newtonian mechanics.

In the simplified, Drude model, the mobility is inversely proportional to the effective mass, for a fixed mean free time.