Band Diagram of a Metal-Semiconductor Contact

[maverick280857]

Hi

In the band diagram of an ideal Metal Semiconductor contact with $\Phi_{M} < \Phi_{S}$ (work function of metal < work function of semiconductor) and a p-type semiconductor, why does the Fermi Level intersect the Intrinsic level right at the metallurgical junction?

Thanks.

 

[sokrates]

There's no requirement as such. The only requirement is that after the necessary charge transfers, the Fermi levels of both materials have to align.

In this particular case, electrons would move from the metal to the p-type SC, because of the particular work functions you chose, and the intrinsic level (as well as the conduction band and the valence bend) would bend downwards. But there's no requirement for the fermi level to cross the intrinsic level right at the junction. This situation would correspond to an extremely specific case, where the charge transfer is 'just enough' to invert the p-type semiconductor to an 'intrinsic' semiconductor at the surface!

of course, when you move along the bulk ( deep down), the band bending would vanish and you'd go back to your original p-type distribution.