Question

# (a) A metal-oxide-semiconductor (MOS) structure is fabricated on an n-type Si substrate. What term is used to describe the surface condition of this MOS structure when negative voltage is applied

at the gate? (b) Draw a band diagram of ideal metal-oxide-semiconductor (MOS) structure fabricated on an n-type Si substrate when a threshold voltage is applied at the gate.Indicate and label the drawing with conduction and valence bands, intrinsic and Fermi levels, build-in potential, applied bias, drop of the potential in the oxide, and surface potential. Indicate also a location of the charges using -' for electron charge and +' for hole charge and write an explanation no longer than 100 words why the charges are in these locations in the structure. How this electrostatic condition is called? (c) An ideal MOS structure has a p-type doped Si substrate with a dopingconcentration of NA = 1 x 1019 cm-3, an oxide layer with a thickness of 2.5 nm andan oxide permittivity of 3.9, and a Si permittivity of 11.5. Calculate the depletionwidth at the threshold (VT) assuming the structure is at room temperature (T =300 K). (d) Calculate the threshold voltage for the same ideal MOS structure as defined in the previous Q2(c), i.e., with a p-type doped Si substrate supplied with a doping concentration of NA = 1 x 1019 cm-³ and a permittivity of 11.5, and an oxide layer with a thickness of 2.5 nm and an oxide permittivity of 3.9.

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