ece340Fall03HW15sol - ECE 340 Homework XV Fall 2003 Due:...

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ECE 340 Homework XV Fall 2003 Due: Monday, November 17, 2003 1. Other than aluminum, polysilicon is another common gate metal for the MOS structure in silicon. By incorporating heavy doping during chemical vapor deposition of polysilicon one can greatly increase the conductivity of the polysilicon “metal”. Accidentally our engineer has made a mistake and heavily doped the polysilicon to be p-type. Reconstruct a diagram similar to Figure 6-17 showing the variation of the metal-semiconductor work function potential difference Φ ms with substrate doping concentration for p + poly-Si. Assume that the Fermi level of p + polysilicon is at the edge of valence band. Show your work and draw to scale with accuracy. Solutions: Fermi level of p + polysilicon is at the edge of valence band, Fermi level of n + polysilicon is at the edge of conduction band, therefore, the new graph is just fig 6-17 shifted up by E g . For n-type silicon: 1.1 ln 0.0259ln 0.55 0.0259ln 22 g dd ms poly s ii i E NN kT n qn n n Φ= Φ − Φ= + = + = + For p-type silicon: 1.1 ln 0.0259ln 0.55 0.0259ln
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ece340Fall03HW15sol - ECE 340 Homework XV Fall 2003 Due:...

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