There are many types of charges in the oxide of the MOS device. They are: fixed oxide charges, mobile ionic charges, oxide trapped charges like electrons and holes, charges at border traps (1-3 nm), and interface trapped charges. To deal with these charges, the simplest distribution assumed is the uniform distribution having a centroid at the middle of the oxide thickness. There is a need to know the actual distribution present in the oxide. Border traps exchange charge with conduction band. These have been introduced in 1992 by D. M. Fleetwod.
I think the oxygen atoms in the oxide near the semiconductor surface will tend to bind with the semiconductor forming a negative charge concentration mono-atomic layer and the insulator at the metal surface may develop a positive charge mono-atomic layer, and the insulator thickness in between would be polarised by these monoatomic charge layers depending upon the polarizability of the insulator oxide material.
Dear Singhal Sir: The interface polarization charge will be I think part of the interface trapped charges. These are important when the interface trap density is very high, like greater than 10^12/cm2eV. Also, they are at the interface anyway, from the distribution-of-charges-in-the-oxide point of view..
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