Photodiode quantum efficiency measures the efficiency with which photodiodes convert incident photons to electrical current, expressed as the ratio between electrons or charge carriers generated by the photodiode and incident photons.
Quantum efficiency can be expressed in percentage terms or as a decimal value between 0 and 1. A quantum efficiency of 1 (or 100%) indicates that every incident photon generates one electron or charge carrier in the photodiode for maximum efficiency; less than this indicates some incident photons do not get converted into electrical current, leading to lower efficiency overall.
Photodiode quantum efficiency depends on many variables, including material properties such as bandgap energy and absorption coefficient, wavelength of incident light, as well as material and design specifications that influence quantum efficiencies at specific wavelengths. Different materials and designs may exhibit differing quantum efficiencies at various wavelengths.
Note that photodiode quantum efficiency should not be confused with external and internal quantum efficiencies (EQE and IQE respectively). While EQE measures how many incident photons convert to electrical current, including those absorbed but not contributing directly, while IQE considers how many photons generate electron-hole pairs regardless of their contribution to photocurrent.
QE photodiode quantum efficiency distinguishes only quantum detectors. Quantum efficiency can be defined as the ratio between photoelectrons generated in a detector and incident photons of radiation; for example, 20% quantum efficiency indicates that every fifth photon will generate photoelectron in it.
The formula for the photodiode quantum efficiency (η) can be expressed as:
η = (Iph / Pin) * (hc / λ)
- Iph is the photocurrent generated by the photodiode (in amperes),
- Pin is the incident optical power on the photodiode (in watts),
- h is Planck’s constant (approximately 6.626 x 10^-34 J·s),
- c is the speed of light in vacuum (approximately 3 x 10^8 m/s),
- λ is the wavelength of the incident light (in meters).
The term (hc / λ) represents the energy of a single photon with wavelength λ, and it is often denoted as E_photon.
The formula quantifies the efficiency of a photodiode in converting incident photons into electrical current. It takes into account the ratio of the generated photocurrent (Iph) to the incident optical power (Pin), as well as the energy per photon. The resulting quantum efficiency provides a measure of how effectively the photodiode converts photons of a particular wavelength into electrical current.