Anonymous @ on
Why is Fermi level always constant in an equilibrium problem?
I find it difficult to visualize (or concretely understand) the fact that Fermi level should universally stay constant in an equilibrium between different materials. I have seen this so many times that it is now a natural part of my analysis when looking at semiconductors from a energy-band perspective, however, when I think of it, it occurs to me that why on earth do we have to line up the electrochemical potential even in materials that have different work functions such as N+ Poly – Oxide – N-type semiconductors (MOS Capacitors)?
Why do we have to start analysing by equating the Fermi levels so that we can justify that we need a flat-band voltage to flatten the bands?
Thank you for the replies.