Question

when the rise of temperature what is the conductivity of intrinsic semiconductor

Answer 1

In conductors, the electron-phonon scattering usually limit the conductivity. As you keep on increase the temperature, the electrons start making collisions with the thermal phonons (generated by the lattice vibrations), which eventually results in reduced mean free path of electrons. The reduction in mean free path of electrons increases the resistivity of conductor.

In intrinsic semiconductors, the carrier concentration in conduction band varies exponentially as:- exp^(-Eg/2kT), where Eg is band gap, kT is thermal energy. So as you keep on increase the temperature, more number of electrons will be excited to conduction band from the valence band. Since there are plenty of empty states available for electrons to occupy in the conduction band and hence there is an increase in conductivity with temperature. In contrast, in conductors electrons are already available in the conduction band and the provided thermal energy due to temperature is transferred to the lattice. The process results in an increase in the electron-phonon scattering.

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Answer 2

At room temperature, a semiconductor has enough free electrons to allow it to conduct current. At or close to absolute zero a semiconductor behaves like aninsulator. ... When the electron is bound, and thus cannot participate in conduction, the electron is at a low energy state