NEET2009PhysicsSemiconductorsActual
A p-n photodiode is fabricated from a semiconductor with a band gap of 2.5 eV . It can detect a signal of wavelength
Options
- A6000 Å
- B4000 ~nm
- C6000 ~nm
- D4000 Å
Correct answer
D. 4000 Å
Step-by-step solution
Key Idea Only signals having wavelength less than threshold wavelength will be detected. Energy aligned & E = hv = h c & = hc E aligned = hc E Substituting the values of and in the above equation = 6.6 10⁻³⁴ 3 10^8 2.5 1.6 10⁻¹⁹ =5000 Å As 4000 Å < 5000 Å Signal of wavelength 4000 Å can be detected by the photodiode.