Polycrystalline silicon has been used as the gate material in Si MOS transistors. It is also used as a barrier layer for making contact to thin Si layers to prevent a metal conductor from penetrating and short-circuiting the thin Si layer. But in MOS, poly-Si gate also gives one more parameter to control the threshold voltage (see next problem).
Thus, construct the equilibrium energy band diagram of a polycrystalline silicon gate MOSC on n-type Si at VG = 0. Do this for four cases.
(a) The Si-gate is doped to the same donor concentration at the n-type Si bulk.
(b) The Si-gate is so heavily doped that its Fermi level is at EC.
(c) The Si-gate is doped to p-type with its acceptor concentration equal to the donor concentration in the n-Si bulk.
(d) The Si-gate is doped to degenerate p-type with EF = Ev.