# Resistivity of doped Si

1. ### liquidFuzz

63
How do I calculate the resistivity of a doped Si if I have to substrate of the same type. Lets say a P and As doped Si. Is the mobility given by, $\mu_n(N_d + N_d)$, or should I do this in an other way? Further, when I calculate the resistivity, is the concentration, $N_{tot} = N_d(P)+N_d(As)$?

Thanks!

2. ### analogdesign

740
The mobility itself is a complicated function of the doping concentration and it depends on the total dopant, not on just Nd or Na. So the way to do it is to get the mobiliity off a curve based on the total doping concentration and then calculate the resistivity using the standard formula. Typically the concentration is completely dominated by one species over another so the answer won't change much as long as you use the highest dopant concentration in the region. This webpage explains the process: http://ecee.colorado.edu/~bart/book/mobility.htm