Quantum efficiency

For the TMR effect of a magnetic tunnel junction, see Tunnel magnetoresistance.
Not to be confused with Quantum yield.

The quantum efficiency (QE) of a photodetector is a measure of its electrical response to light. Another name for it is incident photon to converted electron (IPCE) ratio.

In a charge-coupled device (CCD) or other photodetector, quantum efficiency is the ratio between the number of charge carriers collected at either terminal and the number of photons hitting the device's photoreactive surface. As a ratio, QE is dimensionless, but it is closely related to the responsivity, which is expressed in amps per watt. Since the energy of a photon is inversely proportional to its wavelength, QE is often measured over a range of different wavelengths to characterize a device's efficiency at each photon energy level. For typical semiconductor photodetectors, QE drops to zero for photons whose energy is below the band gap. A photographic film typically has a QE of much less than 10%, while CCDs can have a QE of well over 90% at some wavelengths.

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