# Band bending, depletion layer thickness, density of occupie

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1. Nov 30, 2014

### Red

1. The problem statement, all variables and given/known data
Consider an n-type Si (Eg =1.1eV, ED=EC, εr=11.8) with a bulk doping density ND=1×1017cm-3, a density of acceptor type surface state 1×1014 cm-2 and these states are at the middle of the band gap. Evaluate the amount of:
a) band bending
b)depletion layer thickness
c) density of occupied surface states.

2. Relevant equations
Qss=Qsc=eNDd
band bending, eVs=e2NDd2/2εrε0

3. The attempt at a solution
I attempted to use equation 2 above but there are 2 unknowns in that equation. Not sure what contributes to the Qss=Qsc.

Thank you very much!

2. Nov 30, 2014

### Red

I just found out that it is very easy! Because of the high surface state density, band bending is simply half of Eg, 0.55eV. Now We can use the second equation in ' Relevant equations' to determine the depletion depth d. And then we can find density of occupied surface states, NDd. And there we have it, the solution to this question! HAHA!