its a questionn asking for donor concentration in an Si sample.

it used the equation pho(resistiviy) = 1/sigma(conducitivity) = ( n(concentration) * e ( charge) * u ( mobility) )^-1

where does this equation derive from? i cannot find it anywhere...

 

http://personal.cityu.edu.hk/~appkchu/AP4120/1.PDF

See section 1.7