38. A p−n photodiode is fabricated from a semiconductor with a band gap of 2.5eV. It can detect a signal of wavelength ?

38. A p−n photodiode is fabricated from a semiconductor with a band gap of 2.5eV. It can detect a signal of wavelength ?

(a) 4000 nm

(b) 6000 nm

(c) 4000Å

(d) 6000Å

Answer :  (c) 4000Å

\(E_{\text{photon}} = h\nu\)

\(E_{\text{photon}} = \frac{hc}{\lambda}\)

\(E_{\text{photon}} (\text{eV}) = \frac{12400}{\lambda \text{ in } \text{Å}}\)

\(\lambda = \frac{12400}{2.5}\)

\(\lambda = 5000 \text{ Å}\)