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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

1. 1 × 10¹⁴ Hz
2. 5 × 10¹⁴ Hz
3. 1 × 10¹² Hz
4. 2 × 10¹⁴ Hz

Correct answer: 5 × 10¹⁴ Hz

Solution

The energy of the photon must be at least equal to the band gap energy for absorption. Using the relation E = hν, where h = 6.63 × 10⁻³⁴ J·s and E = 2.0 eV = 2 × 1.6 × 10⁻¹⁹ J, we find ν = E/h ≈ 5 × 10¹⁴ Hz.

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