Quantum efficiency of photo detector


In photo detector quantum efficiency is defined as the number of electron hall pair generated per incident photon of energy hv and is given as ȵ

ȵ = Number of electron hall pair generated /  number of incident photons

    =   I/ q  /  Pin / hv

 I= Average photo current
 Pin = Average optical power incident on photo detector

Absorption coefficient of material determines the quantum efficiency. Quantum efficiency ȵ < 1 as all photons incident will not generate e-h pair. It is normally expressed in percentage.

For example,
On an GaAs photo detector 
Number of photon emitted = 6  × 106 
Average e-h pair generated = 5.4 × 106


ȵ  = 5.4 × 10 /  × 106 

      = 0.9
      
      = 90%

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