7 Interface states

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This again is similar to the preceding examples, but with the addition of a high density of interface states. These are states at the insulator/semiconductor interface which can trap charge, either positive or negative depending upon the position of the chemical potential relative to the band edges at the interface. The applied voltage is 2 V, well into the inversion regime for the sample with no interface states. In the density plot you see a negative spike in the charge density at the interface which shows that the screening of the gate field is accomplished in part by the interface states as well as by the depletion layer, but that there is no longer an electron inversion layer.

Find the value of the Vapplied for which you begin to see the inversion charge. This is the threshold voltage for the MOSFET. Why is the control of interface states a big issue in MOSFET technology?