Redraw Figs. 1. 2 and 3 for the p-channel case (n-type substrate). Figure 1 Band diagram for the ideal MOS structure at: (a) equilibrium; (b) negative voltage causes hole accumulation in the p-type semiconductor; (c) positive voltage depletes holes from the semiconductor surface; (d) a larger positive voltage causes inversion?an "n-type" layer at the semiconductor surface.

Bending of the semiconductor bands at the onset of strong inversion: The surface potential Fs is twice the values of FF in the value of FF in the neutral p material.

Figure 3 Approximate distributions of charge, electric field, and electrostatic potential in the ideal MOS capacitor in inversion. The relative width of the inverted region is exaggerated for ilustrative purposes, but is neglected in the field and potential diagrams. The slopes of the band edges reflect the electric fields in the gate dielectric and the semiconductor channel. The product of the perpendicular electric field and dielectric constant (known as the displacement) is continuous acros the dielectric?semiconductor interface if there are no charges at the interface, according to Maxwell's boundary conditions.

(V=0) (a) Em 1 qpi Ec -E En E, Metal Oxide Semiconductor (b) V 0 qV Efm! M 100 S Depletion Ec E EA E, (d) V>>0 Ege qv M 100 O S Inversion Ec E Ep E, t 94 Oxide Semiconductor qbF -Ec -Ei -EF -E V>>0 EFm M x Ec E -En E Charge Density Electric Field Electrostatic Potential Q (charge per unit area) 4& 4V (x) W W x x