# Energy gap calculation for semi-conductors.

1. Oct 16, 2011

### NewtonianAlch

1. The problem statement, all variables and given/known data
Most solar radiation has a wavelength of 1 µm or less.

(a) What energy gap should the material in a solar cell have if it is to absorb this radiation?
(b) Is silicon an appropriate solar cell material?

Explain your answer.

2. Relevant equations

f = c/lambda
E = hf

3. The attempt at a solution

a) f = 3E8/1000E-9 = 3E14 Hz

E = hf

So E ≤ 1.24eV

b) Yes, because silicon has an energy-gap of roughly 1.14 - 1.17eV so 1.24eV is enough to excite the electrons in to the conduction band.

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What I don't fully understand is if the wavelength is below this 1000nm mark, the associated energy gap is going to increase, very quickly certain wavelengths aren't going to be absorbed by silicon for it to act as a semi-conductor. So I'm thinking my answer is wrong?

For e.g. if the wavelength was 700nm, then E = 1.77eV, and silicon and a lot of other semi-conductors wouldn't be able to utilize these kinds of wavelengths.

2. Oct 17, 2011

### NewtonianAlch

Nvm, I found out that most solar cells have layers of other material to absorb different wavelengths to be more efficient, so it was correct.

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