GATE 2014 EC (EC4) – Question 20
Find the cutoff wavelength (µm) for intrinsic excitation of a semiconductor with bandgap E_g = 1.1 eV.
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Correct answer: 1.12 to 1.14
Explanation
The longest wavelength producing intrinsic excitation satisfies hc/λc=Eg. Using hc≈1.24eV·µm gives λc≈1.24/1.1=**1.1273µm**. Photons at longer wavelengths have insufficient energy to bridge the bandgap.