Regarding photodetectors, it is possible to speak of current response in units of incident optical power.
In the first English texts concerning optoelectronics, current response as a function of optical power (A/W) of a photodetector was called sensitivity. This significant term was gradually replaced by responsivity, which more specifically describes the sensitivity of a photodetector. This nomenclature will be adopted in this text.
For photodetectors, it is also possible to speak of quantum efficiency, expressed as:
–np= number of electron-hole pairs generated per second;
-φ = number of incident photons per second.
The relation between quantum efficiency and responsivity Rpd in A/W is:
– q= electron charge = 1.602×10-19 C;
– h = Planck’s constant = 6.626×10-34 J/s;
ν= light wave frequency in hertz.
Responsivity takes into account the frequency of the light wave. Consequently, by referring to Table 5.1, it should be noted that for a quantum efficiency of 100%, the responsivity of an optical photodetector at 1.55 µm is 1.25 A/W, whereas to obtain identical quantum efficiency the responsivity of a photodetector at 0.8 µm is only 0.64 A/W.
In the sections below, quantum efficiency notion is used for photodiodes, ...