Physics of Semiconductor Devices

MOS capacitor

A MOS capacitor consists of an aluminum layer, a n++ Si layer, a 2 nm thick SiO₂ layer, and a p-doped silicon substrate where N_a = 4.0×10¹⁶ cm^-3. The contact between the aluminum and the n++ region is a tunnel contact.

(a) Draw the band diagram (conduction band, valence band) for zero applied bias voltage. Is the MOS capacitor in accumulation, depletion, or inversion?

(b) Draw the band diagram at the flatband voltage indicating the voltage that would have to be applied.