Question

Three phtodiodes D₁, D₂, D₃ are made of semiconductors having band gaps of 2.5 eV, 2 eV and 3 eV respectively. Which one will be able to detect light of wavelength 600 nm?

• A. D₁ only
• B. Both D₁ and D₃
• C. D₂ only
• D. All the three diodes

Answer 1

The Correct Option is C

Explanation: To determine which photodiode can detect light of wavelength 600 nm:

1. Calculate photon energy (E): 
   \( E = \frac{hc}{\lambda} \), where \( hc = 1240 \, eV·nm \), \( \lambda = 600 \, \text{nm} \). 
   \( E = \frac{1240}{600} \approx 2.07 \, \text{eV} \).
2. Compare with band gaps:
   • D₁ (2.5 eV): Photon energy (2.07 eV) < band gap → No detection.
   • D₂ (2 eV): 2.07 eV > band gap → Detection possible.
   • D₃ (3 eV): 2.07 eV < band gap → No detection.

Only D₂ (2 eV band gap) can detect 600 nm light.