A pure semiconductor germanium or silicon, free of every impurity is called intrinsic semiconductor. At room temperature, a pure semiconductor has very small number of current carriers (electrons and holes) .Hence its conductivity is low. When the impurity atoms of valance five or three are doped in a pure semiconductor, we get respectively n- type or p- type extrinsic semiconductor. In case of doped semiconductor n_e.n_h = n_i². Where n_e and n_h are the number density of electron and hole charge carriers in a pure semiconductor. The conductivity of extrinsic semiconductor is much higher than that of intrinsic semiconductor.

At absolute zero, what is the nature of silicon?

insulator

$\text{At 0K , Thermal energy of electron is zero.Hence No Electron can jump from valence to conduction band}$

$\Rightarrow Conductivity = 0$