Question

A p-n photodiode is fabricated from a semiconductor with band - gap of 2.8 eV . Can it detect a wavelength of 6000nm?

Answer 1

No, the p-n photodiode cannot detect a wavelength of 6000 nm.

The reason is explained below:

• As per the question,

       The energy band gap of the given p-n photodiode ( Eg ) = 2.8 eV

       Given wavelength ( λ ) = 6000 nm = 6000 × 10⁻⁹ m

• We know that the energy of a signal is represented as E = hc / λ where h is the Planck’s constant (6.626 × 10⁻³⁴ Js) and c is the speed of light (3 × 10⁸ m/s).

• Therefore, E = 6.626 x 10⁻³⁴ x 3 x 10⁸ / 6000 x 10⁻⁹

                             = 3.313 x 10⁻²⁰ J

• Also 1.6 × 10⁻¹⁹ J = 1 eV

• Therefore, E = 3.313 × 10⁻²⁰ J

                              = 3.313 x 10⁻²⁰ / 1.6 x 10⁻¹⁹

                              = 0.207 eV

• This shows that the energy of the signal having wavelength 6000 nm is 0.207 eV, which is less than given band gap( 2.8 eV ).

• Hence, the p-n photodiode cannot detect the signal of 6000nm.