Calculating Resistivity of Doped Si: P and As Substrate Comparison"

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SUMMARY

The discussion focuses on calculating the resistivity of doped silicon (Si) substrates, specifically comparing phosphorus (P) and arsenic (As) doping. The correct approach involves determining the mobility from a curve based on the total doping concentration, rather than using a simplified formula like \mu_n(N_d + N_d). The total concentration should be calculated as N_{tot} = N_d(P) + N_d(As), but the resistivity calculation is primarily influenced by the highest dopant concentration. For detailed methodology, refer to the provided resource on mobility.

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How do I calculate the resistivity of a doped Si if I have to substrate of the same type. Let's 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!
 
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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
 
Most likely this can only be answered by an "old timer". I am making measurements on an uA709 op amp (metal can). I would like to calculate the frequency rolloff curves (I can measure them). I assume the compensation is via the miller effect. To do the calculations I would need to know the gain of the transistors and the effective resistance seen at the compensation terminals, not including the values I put there. Anyone know those values?

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