The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 nm is incident on it. The band gap in (eV) for the semiconductor is (a) 2.5 eV (b) 1.1 eV (c) 0.7 eV (d) 0.5 eV

Answer: (d). Conductivity rises only when photon energy ≥ Eg, so Eg = hcλmax. Eg(eV) = (1240)/(λ(nm)) = (1240)/(2480) Eg = 0.5 eV So the answer is (d) 0.5 eV.

The electrical conductivity of a semiconductor increases when… | JEE Main 2005 (AIEEE)

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Energy Bands in Solids

The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than $2480\text{ nm}$ is incident on it. The band gap in $(\text{eV})$ for the semiconductor is

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Answer: (d)

Conductivity rises only when photon energy $\ge E_g$ , so $E_g = \dfrac{hc}{\lambda_{max}}$ .
$E_g(\text{eV}) = \dfrac{1240}{\lambda(\text{nm})} = \dfrac{1240}{2480}$
$E_g = 0.5\text{ eV}$
So the answer is (d) $0.5\text{ eV}$ .

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