My professor says in his notes that, because electron mobility decreases when temperature increases high enough, the conductivity of an extrinsic semiconductor actually decreases at such temperatures.
I looked that up on Google, Wikipedia, and in our textbook, but the sources I found barely agree to that. The closest statements I found to that effect were in Electron mobility, that yes, the mobility decreases after a certain temperature, but:
The effect of ionized impurity scattering, however, decreases with increasing temperature because the average thermal speeds of the carriers are increased. Thus, the carriers spend less time near an ionized impurity as they pass and the scattering effect of the ions is thus reduced.
In addition, our textbook says that when doped with a high enough concentration, an extrinsic semiconductor starts to behave like a conductor!.
So it's clear that there are many, many factors in play. What I want to know is: Is my professor justified in his claim that the resistance of an extrinsic semiconductor might increase with temperature?