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A p-n photodiode is made of a material with a band gap of 2.0 eV. The minimum frequency of the radiation that can be absorbed by the material is nearly

Asked in NEET 2008 · Photodiode and solar cell

Answer: (4) 5×10¹⁴ Hz

Step-by-step solution

Idea: absorption starts at the frequency whose photon energy just equals the gap, so set h u=E_g.

Find the matching wavelength first: λ=(hc)/(E_g)=(12400 eV A)/(2.0 eV)=6200 A.

u=c/λ=(3×10⁸)/(6200×10⁻¹⁰).

u=4.84×10¹⁴ Hz≈5×10¹⁴ Hz.

Anything below this is too weak per photon; anything above is absorbed.

Why the other options are wrong

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