Work function, Fermi levels and the MOS capacitor

[SMOF]

Hello.

I am doing an electronics degree, and we were told in our solid state devices class that "work function is the energy required to release an electron from the influence of the material to vacuum. When the system is brought together to form the MOS capacitor, the Fermi levels must equalise by transfer of negative charge from the material with the lower work function (metal) to the material with the higher work function (silicon)."

But I don't understand why it of from the lower to the higher, I would have thought it would have been from the higher to the lower.

Can anyone give me some guidance on this? It would be much appreciated.

Thanks in advance.

Seán

 

[BigJDubs]

Generally speaking, electrons always flow from higher energy to lower energy. In this case, the work function is a measure of the energy required to release an electron from the material. The material with the lower work function has less energy required, and thus electrons will flow from the material with the higher work function to the material with the lower work function. This equalizes the two Fermi levels.