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### 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 / Eg  = 1.24 / Eg

Where,

Eg  = 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  Eg  = 1.43 eV, hc = 1.24 , find cut of wavelength = ?

Cut of wavelength = hc / Eg  = 1.24 / Eg

= 1.24 / 1.43

= 0.867 micro meter

= 867 nm
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 / Eg  = 1.24 / Eg

Where,

Eg  = 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  Eg  = 1.43 eV, hc = 1.24 , find cut of wavelength = ?

Cut of wavelength = hc / Eg  = 1.24 / Eg

= 1.24 / 1.43

= 0.867 micro meter

= 867 nm