Physics Help Forum Band gap
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 Dec 7th 2016, 11:10 PM #1 Junior Member   Join Date: Oct 2016 Posts: 3 Band gap ZnO is a semiconductor material that has a band gap of 310 kJ/mol. What is the longest wavelength of light, in nm, that will excite an electron from the valence band to the conductance band?
Dec 8th 2016, 11:19 AM   #2

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 Originally Posted by starrysky ZnO is a semiconductor material that has a band gap of 310 kJ/mol. What is the longest wavelength of light, in nm, that will excite an electron from the valence band to the conductance band?
Your unit is wrong. A band gap is defined as the energy to promote an electron from the top/bottom of one band (valence, conduction, etc) to the bottom/top of another. kJ/mol is not an energy.

310 kJ is an awesomely huge band gap. Might we be talking about 310 x 6 x 10^{-23} kJ? That's an awesomely small band gap. I'll leave that one for you to talk to your instructor about.

Anyway, we know that the energy of the photon is $\displaystyle E = \frac{hc}{\lambda}$. So the largest possible $\displaystyle \lambda$ will be for the smallest possible energy jump. So what's E?

-Dan
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