## Mobility of electrons and holes

Problem:
Calculate mobilities of electrons and holes (assuming equal) in grey tin, silicon and germanium. Calculate also the mobility that would be necessary for diamond to have an intrinsic conductivity of 10-12 S m-1 if the hole and electron mobilities were equal.

Working:
$$\sigma$$ = Nc (e$$\mu$$n*e$$\mu$$p)exp(−Eg /2kT)

$$\sigma$$= 10-12
e = 1.6*10 -19
k = 1.38*10 -23
T = 300K
Nc = 2.5*1025
Eg(tin) = 0.08
Eg(silicon) = 1.11
Eg(germanium) = 0.66

For tin
Rearrange to give:

$$\mu$$np = $$\sigma$$ / 2e Nc exp(−Eg /2kT)

The exponential becomes equal to zero...

I'm quite sure i'm missing something relatively simple here but not sure what
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 It appears i was using wrong values for the conductivity and boltzmann constant, got the correct answer now.