= Solution
An <intrinsic semiconductor> has thermally generated conduction <electrons> and valence holes, with $n=p=n_i$ at equilibrium in the ideal undoped neutral material. Their abundance is controlled by its <band gap>, <temperature> and band <density of states>.
An <extrinsic semiconductor> has its mobile carrier populations substantially modified by electrically active impurities. A <donor impurity> can supply <electrons>, producing n-type material; an <acceptor impurity> can capture a valence <electron> and leave a mobile <electron hole>, producing p-type material. Compensation and incomplete ionization can modify these simple counts. At low <temperature> <dopant freeze-out> can occur; at sufficiently high <temperature> intrinsic pair production can overwhelm a fixed dopant density. Doping and the dominant transport regime are related but are not interchangeable descriptions at every <temperature>.
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