Chapter 6 Lecture - Part 1

The modified work function describes the energy

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Unformatted text preview: (b) onset of saturation at pinch-off, VG > VT and VD = (VG VT); (c) strong saturation, VG > VT and VD > Band Diagrams for MOS Capacitors Band • Analysis using Energy Band Diagrams – Modified work functions for the metal and Modified semiconductor layers are used. The modified work function describes the energy required to move electrons from the associated Fermi level to the conduction band of the insulator conduction • qΦm is the modified work function for metal • qΦs is the modified work function for the semiconductor semiconductor • in the semiconductor, qΦF = Ei – EF Band Diagrams for MOS Capacitors Band • V < 0 (Accumulation) – – – – holes accumulate on the semiconductor side of holes the SC/Insulator interface. Called hole accumulation. accumulation. EF is raised by an amount qV due to electrons accumulating at the metal/SC interface. accumulating The charge accumulation results in an electric The field across the insulator field The E field causes a gradient in the oxide The conduction band. conduction Band Diagrams for MOS Capacitors Band – – • Hole accumulation requires that the difference Hole between EF and Ei to increase in the accumulation between region. This happens by band bending in this region. The bands bend to reflect the distribution of charge carriers in the semiconductor. of For hole accumulation in p-type material, the For bands bend upward. bands V>0 – – (Depletion) EF of the metal is lowered by qV as a result of the positive voltage positive Negative charge accumulates at the surface of the Negative semiconductor in response to the charge. semiconductor Band Diagrams for MOS Capacitors Band – In p-type material, this results in the depletion of In holes at the interface. The negative charge results from uncompensated ionized acceptors in this region and electrons accumulating there. region – An E field is created and the energy levels in the An insulator has a gradient insulator – In the semiconductor, EF remains fixed. The energy bands bend downward to reflect th...
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