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GATE 2026 EC – Question 54

Electronic Devices · P-N Junction and Semiconductor Devices · 2 marks · Multiple select

Consider an LED based on a direct bandgap semiconductor material with energy bandgap 1.3 eV. Given: Plank’s constant, $h=6.63\times10^{-34}$ J s and speed of light in free space is $3\times10^8$ m s$^{-1}$. In which of the following wavelength ranges the LED will NOT emit?

  1. 1410 ± 20 nm
  2. 1090 ± 20 nm
  3. 950 ± 20 nm
  4. 510 ± 20 nm

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Correct answer: (A) 1410 ± 20 nm; (B) 1090 ± 20 nm

Explanation

$\lambda_g=hc/E_g=1.989\times10^{-25}/(1.3\times1.6\times10^{-19})\approx956$ nm. Photons with wavelength longer than 956 nm have energy below the bandgap and cannot be emitted, which rules out 1410 nm and 1090 nm. Emission occurs near 950 nm.