Question

What would be the ideal wavelength range for Si and GaAs photodiodes to produce maximum currents?

Please show logic and or calculations

Answer 1

* The photo diode works on the principle that when light is incident on the material, electrons absorb the light energy and gets excited to conduction band.

* So the photon should have enough energy to excite the electrons from valence band to conduction band.

* So suitable wavelength should be selected for each material such that photon energy should be equal or more than the band gap energy.

* So

                                                                                         

Or

                                                                                         

For Si, E_g = 1.12eV. So

                                                 

Or

                                                                                   

For GaAs, E_g = 1.42eV. So

                                                 

Or