# Is the following semiconductor n-type or p-type?

1. May 17, 2016

### sa1988

1. The problem statement, all variables and given/known data

Estimate the carrier density and mobility of a semiconductor with a Hall coefficient of $R_{Hall} = 7*10^{-5} m^3C^{-1}$ and a conductivity $\sigma = 200 (\Omega m)^{-1}$. Is the semiconductor n-type or p-type?

2. Relevant equations

$R_{Hall}=\frac{1}{ne}$
$\sigma=ne\mu_e + pe\mu_h$

3. The attempt at a solution

Given the request at hand, and going by many of the examples given in lectures, I figured the conductivity can be simplified to $\sigma = 2ne\mu$, then from the given information I can use the $R_{Hall}$ equation to find $n$ then sub into the $\sigma$ equation and rearrange to find $\mu$.

$n = 8.1*10^{21} m^{-3}$
$\mu = 0.007 m^2/Vs$

From this, how can I know if it's a p-type or n-type semiconductor? According to all the info I can find, the calculation I've just done is based on the assumption that I'm working with an intrinsic semiconductor which means it isn't n-type or p-type because $n=p$. So I must be going wrong with the assumptions I've made in simplifying the calculation..? I'm not sure what I'm missing.

Thanks.

2. May 17, 2016

### sa1988

Ah, I've cracked it.

The Hall coefficient is a positive value which means we're working with positive charge carriers. So it's p-type.

Also I think this means I should not use the factor of 2 in the conductivity equation and simply use $\sigma = pe\mu$