Module 9 : Photo Detectors
Lecture : Principle of Photo Detection
   
9.3 Performance Parameters :
 


The performance of a detector is described in terms of certain figures of merit .


Responsivity :
Responsivity of a detector is given as the ratio of the generated photocurrent ( $ I$) to the amount of optical power ( $ P_0$) incident on the detector

$\displaystyle {\cal R} = \frac{I}{P_0}$

The unit of responsivity is amperes/watt.

Quantum Efficiency :
A detector is not capable of collecting all the photons and convert them to electron-hole pairs. The number of electrons produced per incident photon is defined as the quantum efficiency , which is usually expressed as a percentage

$\displaystyle \eta = \frac{{\rm No. \ of\ electrons\ produced}}{{\rm No.\ of\ incident\ photons}} (\times 100\%)$

If $ I=$photocurrent in the external circuit and $ P_0=$the incident optical power (dropping the percentage in the definition,)

$\displaystyle \eta = \frac{I/q}{P_0/h\nu}$
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