Q. A p-n photodiode is fabricated from a semiconductor with a band gap of 2.5 eV. It can detect a signal of wavelength:
A) 4000 nm
B) 6000 nm
C) 4000 Å
D) 6000 Å
Explanation
[Solution from source] The longest detectable wavelength is λ = hc/Eg = 1240 eV nm/2.5 eV ≈ 496 nm ≈ 5000 Å. Only photons of shorter wavelength have enough energy, so 4000 Å (400 nm) is detected. 6000 Å and the nm values of 4000 and 6000 are all longer than the cut-off. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.