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  4. A p-n photodiode is fabricated from a semiconductor with band gap of 2.8 eV . Which of the following wavelength it can detect?

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Q. A $p-n$ photodiode is fabricated from a semiconductor with band gap of $ 2.8\,eV $ . Which of the following wavelength it can detect?

Delhi UMET/DPMTDelhi UMET/DPMT 2009

Solution:

Given, $E=2.8\, eV $
$=2.8 \times 1.6 \times 10^{-19}$
Energy $E=\frac{h c}{\lambda}$
$\therefore \lambda=\frac{6.6 \times 10^{-34} \times 3 \times 10^{8}}{2.8 \times 1.6 \times 10^{-19}}$
$=440 \times 10^{-9} m =440 \,nm$