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Metal–Oxide–Semiconductor structure
From Wikipedia, the free encyclopedia
A Metal–Oxide–Semiconductor (MOS) structure is obtained by depositing a layer of dielectric (usually silicon dioxide, SiO2) and a layer of conductor (nominally metal but usually polycrystalline silicon) on top of a semiconductor (usually silicon) substrate. Its structure is equivalent to that of a plane capacitor with one of the electrodes replaced by a semiconductor.
When a voltage is applied across a MOS structure, it modifies the distribution of charges in the semiconductor. If we consider a P-type semiconductor (with NA the density of holes), a positive VGB (see figure) tends to reduce the concentration of holes, typically depleting the concentration to near zero in some part of the semiconductor. If VGB is high enough, the concentration of negative charge carriers is more than that of positive charges.
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