EducationWhat is Photodiode quantum efficiency

What is Photodiode quantum efficiency

Category articles

When diving into the world of photonics, understanding the behavior of photodiodes and their response to light is crucial. At the heart of this is the concept of “photodiode quantum efficiency.” This article breaks down its significance, factors influencing it, and how it stands in comparison to other quantum efficiencies.

What is Photodiode Quantum Efficiency?

Photodiode quantum efficiency (QE) is a measure of how efficiently a photodiode converts incident photons into electrical current. Simply put, it expresses the ratio between the number of electrons or charge carriers generated by the photodiode to the number of incident photons.

  • Quantum efficiency can be represented in two ways:
    • As a percentage: Ranging from 0% to 100%.
    • As a decimal value: Ranging between 0 and 1.

For instance, a quantum efficiency of 1 or 100% means that every photon incident on the photodiode produces one electron or charge carrier, achieving optimal efficiency. Any efficiency below this benchmark means that not all photons are converted into electrical current, resulting in reduced overall efficiency.

Factors Influencing Photodiode Quantum Efficiency

The quantum efficiency of a photodiode isn’t a fixed value; it varies based on:

  • Material properties: These include aspects like bandgap energy and absorption coefficient.
  • Wavelength of incident light: Photodiodes might have different efficiencies for different light wavelengths.
  • Design and material specifications: They determine the photodiode’s response at specific wavelengths.

Different materials and design innovations might showcase varied quantum efficiencies across different wavelengths.

Photodiode Quantum Efficiency Vs. Other Quantum Efficiencies

While “photodiode quantum efficiency” is a term often thrown around, it’s essential not to muddle it with related concepts:

  • External and Internal Quantum Efficiencies (EQE and IQE):
    • EQE assesses how many incident photons get converted into electrical current, including those that are absorbed but don’t directly contribute.
    • IQE gauges the number of photons creating electron-hole pairs, irrespective of their direct contribution to the photocurrent.
  • Laser Quantum Efficiency:
    • In the realm of lasers, quantum efficiency indicates the fraction of input photons that contribute to a desired outcome. For instance, in laser gain media, it could represent the portion of absorbed pump photons aiding the laser’s operation. In some rare scenarios, energy transfer processes between laser-active ions can lead to quantum efficiencies exceeding 100%.

Quantum Efficiency in Practice

Using a practical example: if a photodiode has a 20% quantum efficiency, it implies that for every five photons striking it, one generates a photoelectron.

The sensitivity of detectors, like photodiodes, can be expressed in various terms across datasheets, from A/W to quantum efficiency. It’s essential to grasp these concepts to make informed decisions in photonics applications.

Photodiode quantum efficiency is a cornerstone concept in understanding light detection and conversion. By familiarizing yourself with its intricacies, you’re well on your way to mastering the behavior of photonic devices.

Calculating Photodiode Quantum Efficiency

To calculate the photodiode quantum efficiency (QE), one needs to understand its relation to the device’s responsivity. The formula to determine quantum efficiency is given by:

Q.E.=1240×(λ / Rλ)​


  • Q.E. represents the Quantum Efficiency.
  • Rλ is the photodiode’s responsivity, typically given in A/W (Amperes per Watt).
  • λ is the wavelength of the incident light, measured in nanometers (nm).

In essence, this equation provides a link between the photodiode’s ability to generate current (responsivity) and the number of incident photons at a specific wavelength. By using the formula, one can ascertain the efficiency with which the photodiode operates under particular light conditions. It’s crucial to ensure that the wavelength used in the equation corresponds to the wavelength at which you want to determine the quantum efficiency, as this value can vary across different wavelengths.

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.

Michal Pukala
Electronics and Telecommunications engineer with Electro-energetics Master degree graduation. Lightning designer experienced engineer. Currently working in IT industry.