most capacitance varies with frequency at low frequency it has high value in comparasion to high frequency
Majority carriers, minority carriers, and interface states contribute to the MOS or MOSFET capacitance. Majority carriers can follow very high frequencies, but the minority carriers and a part of the interface states cannot follow high frequencies. This is why the contribution to capacitance from the interface states will be absent at high frequencies and also from the minority carriers in the MOS capacitor, but not in the MOSFET as the minority carriers are injected by the source into the MOSFET channel in strong inversion.
In case of a MOS capacitor the inversion charge is contributed by the minority carriers which have a definite generation and recombination rate. Now when the frequency applied becomes greater then that rate the inversion charge cannot follow the change and therefore the capacitance is solely determined by the depletion capacitance. In case of MOSFET in this condition the inversion charge is provided by the majority carriers in the source.
Samares Kar sir , why will minority carriers and interface states contribute only to lower frequency, why do they remain inactive at higher frequency. can you please help me understand ?
There are a lot of arguments, one of them the higher frequency has high resistivity, which inactive the minority carriers rapidly at the interface between oxide and semiconductor.
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