Electron concentration in p-type semiconductor

[Philmac]

Electron concentration in n-type semiconductor

Homework Statement

At T = 0 K, what is the electron concentration in a Si semiconductor that is doped with Phosphorus atoms at ND=1017 cm^-3? At room temperature, what is the electron concentration of this semiconductor? The electron mobility of Si is 1350 cm2/Vs, calculate the resistivity of this semiconductor.

Just the bolded part. I'm not sure if the information in the second sentence is relevant to the first part.

Homework Equations

In the course notes I'm given dozens of equations, but I don't see how any of them would be useful for this question.

The Attempt at a Solution

I'm totally clueless, don't even know where to begin.

 

[Mike Cookson]

Two things have popped into my head.

1. In a doped semiconductor you can assume that the concentration of carriers is approximately equal tot he concentration of donars (assuming that the donars each produce one carrier) - i.e. Nd = p (approx.)

2. Surely at 0K all of the electrons would be localised to their parent atoms? In order to create holes in the valence band which electrons need to be elevated to the energy level of the Phosphorus, but at 0K with no other excitation there is no energy for the electrons to use to get to the energy level. I can't make my mind up whether this effects the concentration or not.