GATE 2022 IN – Question 27
A photodiode is made from a semiconductor of bandgap 1.42 eV. Given Planck’s constant $6.626\times10^{-34}$ J·s, vacuum light speed $3\times10^8$ m/s, and 1 eV $=1.6\times10^{-19}$ J, its cutoff wavelength is ______ nm (one decimal place).
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Correct answer: 870.0 to 880.0
Explanation
A photon must supply at least the bandgap energy.
Thus λc=hc/Eg=(6.626×10⁻³⁴×3×10⁸)/(1.42×1.6×10⁻¹⁹)=874.912 nm. Rounded, **874.9 nm**.