Effects of temperature on the conductivity of semiconductors is
,when their is a change in temperature ,it changes the electrical conductivity of semiconductors.
- At absolute zero(0 K)
At absolute zero temperature all the electrons of semiconductors are held tightly by the atoms. Inner Orbit electrons bound to Nucleus whereas, the valence electrons are bound by covalent bonds.Therefore no free electron is available in semiconductor for conduction.Hence it behaves as insulator.
shown by energy band diagram,
at absolute zero temperature, valence band is completely filled whereas, conduction band is totally empty. Since no energy is supplied to the semiconductor ,so electron can’t cross forbidden energy gap.Thus, there is no free electrons in the semiconductor for conduction at absolute zero. So semiconductor behaves as an insulator at absolute zero temperature.
When temperature is increased: When temperature is increased ,some of the covalent bonds break down due to thermal energy supplied to semiconductors.Now electrons become free, which were engaged in formation of bonds. Thus at high temperature semiconductor no longer behaves as insulator
- At higher temperature, electrons from the valence band jumps to the conduction band and become free.Since they have acquired heat energy.The higher the temperature greater is the number of free electrons in the conduction band.So,At higher temperature semiconductor starts conducting.
At room temperature:
So at room temperature, electrons acquired some heat energy and jumps from Valence band to conduction band . But very less electrons exist in semiconductor at room temperature, therefore ,the conductivity of semiconductor is very small.So the current through a semiconductor is too small at room temperature.
When energy is supplied to a semiconductor, a valence electron jumps from valence band to conduction band. The departing electron, leaves the vacancy in the valence band,this vacancy is known as a hole.
Thus, “hole is a vacancy left in the valence band because of lifting of electron from Valence band to conduction band“.
when some energy is supplied to a semiconductor, its valence electron jumps from Valence band to conduction band and becomes
free.Simultaneously a hole is created in valence band.
Whenever, electron is lifted to conduction band , a hole is created in valence band and each time an electron -hole pair is formed.This pair is known as electron-hole pair.