## p-type semiconductors

A forum designed mainly for high school physics students in New South Wales, Australia.
r.jenkins
Posts: 11
Joined: Sat May 01, 2010 10:43 pm

### p-type semiconductors

Hi,
I understand with n-type semiconductors how there is a free unbonded electron introduced by the group 5 dopant which can easily move under an applied voltage, but with p-type I can't see any reason why electrons (and positive holes) would want to move?

Thanks
joe
Posts: 755
Joined: Fri Aug 29, 2003 11:57 am
Location: Sydney

### Re: p-type semiconductors

As with n-type, there is no collective electron motion in p-type semiconductors unless there is an electric field. When an electric field is applied, some electrons are accelerated to a drift velocity determined by the field and the interaction with the lattice: see
Because of length limits, I'll continue on another message

Joe
joe
Posts: 755
Joined: Fri Aug 29, 2003 11:57 am
Location: Sydney

### Re: p-type semiconductors

Continued:

So perhaps your question is "why does doping lead to greater drift velocity?" to which the answer is that the presence of holes gives the electrons somewhere to go.

Here's an analogy.
In the absence of gravity, take a full bottle of water (analogy of undoped semiconductor) and a bottle of water in which holes are distributed (.. doped semiconductor). While holding the bottle stationary, apply a gravitational field (.. electric field). The gravitational field produces a force on the water. In the full bottle, water does not move, because there is nowhere for it to go. In the bubble bottle, the water moves down (.. electrons move to higher potential) and so the bubbles move up (.. holes move to lower potential).

I haven't understood your question (obviously you're not really psychoanalysing electrons) but I hope that answers it.

Joe
Mini
Posts: 66
Joined: Sat Mar 06, 2010 10:33 am

### Re: p-type semiconductors

Having done the HSC "Physics" course, I don't think drift velocity is in the course.