Exploring PN Junction Loop: Fermi Level and Work Function

[daudaudaudau]

Hi. So we have all seen the band diagram of a PN junction. In order for the fermi level to be the same on both sides, the P bands are shifted up or the N bands are shifted down. Now that the fermi levels are equal, what would happen if you bent the diode into a ring (annulus) shape? How would the bands look that the second junction? Since the fermi levels are already aligned, it's hard for me to understand.

Another thing that's puzzling me is the work function, i.e. the energy difference between the fermi level and the vacuum level. The work functions of N and P type Si are different. But what if we imagine a 1 meter long PN junction. If you measure the workfunction at either end, will you get the same number? I'm thinking you should since the fermi levels are equal.

 

[BigJDubs]

In answer to your questions, when you bend a PN junction into a ring, the bands will still be shifted in order to maintain the same Fermi level on both sides. The bandgap of the second junction will be the same as the first. This means that the band alignment will still be the same and the charges can still flow through the junction.As for the work function, the work function at either end would be the same. This is because the Fermi level is equal on both sides of the junction, meaning that the energy difference between the Fermi level and the vacuum level is constant throughout the junction.