Cut-off wavelength of photo detector

A cut of the wavelength of any photodetector can be defined as if any particular semiconductor can be absorbed photon over a limited wavelength range. The highest bandwidth is known as cut-off wavelength.

Cut off wavelength is determined by band gap energy Eg of a material.

      Cut of wavelength = hc / E_g  = 1.24 / E_g  

Where,

E_g  = Electron volts (eV) 

A typical value of cut of wavelength for silicon is 1.06 micrometer and germanium is 1.6 micrometer.

For example :

In PIN photo diode  E_g  = 1.43 eV, hc = 1.24 , find cut of wavelength = ?

 Cut of wavelength = hc / E_g  = 1.24 / E_g

                                                

                                               _{= 1.24 / 1.43}

                    

                                                _{= 0.867 micro meter}

                       

                                                _{= 867 nm}