Surface Space-Charge Region in Thermal Equilibrium
Due to the low carrier densities in non-degenerately doped semiconductors, spatially extended space-charge layers may be present at semiconductor surfaces and interfaces. The resulting band bending is obtained by solving Poisson’s equation. In thermal equilibrium, the space charge is balanced by a net charge in electronic surface or interface states. Depending on the sign and the magnitude of the surface band-bending, accumulation, depletion, and inversion layers are to be distinguished. Larger carrier concentrations in accumulation and inversion layers lead to quantum size-effects.
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