MOS structure

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accommodate the gate voltage applied. Part of this bending occurs in the semiconductor

and the rest in the oxide. The metal and the semiconductor affinity remain the same (see

Figure 3.).

Figure 3.

Energy band diagram and charge distribution in an ideal MOS capacitor

in accumulation condition.

The negative charge on the gate creates an opposite charge on the semiconductor

(enhanced concentration of holes near the oxide interface). When a small positive bias is

applied to the gate, holes are pushed away from the oxide interface and create a depletion

layer in the semiconductor, consisting on the negative charges due to the acceptor ions. The

energy band diagram and the charge distribution are shown in Figure 4.

Figure 4.

Energy band diagram and charge distribution in an ideal MOS capacitor

in accumulation condition.