Semiconductors

JEE Main level, single correct, medium

119 of 209

Question 119 of 209

Conductivity of a photodiode starts changing only if the wavelength of incident light is less than 660nm.660nm. The band gap of photodiode is found to be (X8)eV.\left(\dfrac{X}{8}\right)eV. The value of XX is:
(Given h=6.6×10−34Js,e=1.6×10−19Ch=6.6\times {10}^{-34}Js,e=1.6\times {10}^{-19}C)

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Answer: (A) 1515

Given: Threshold wavelength =660nm=660nm.
Therefore, energy required(or band gap energy) Eg=hcλ=6.6×10−34×3×108660×10−9J{E}_{g}=\dfrac{hc}{\lambda }=\dfrac{6.6\times {10}^{-34}\times 3\times {10}^{8}}{660\times {10}^{-9}}J
=6.6×10−34×3×108660×10−9×1.6×10−19eV=\dfrac{6.6\times {10}^{-34}\times 3\times {10}^{8}}{660\times {10}^{-9}\times 1.6\times {10}^{-19}}eV
=158eV=\dfrac{15}{8}eV
So, X=15X=15.

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