External Quantum Efficiency

Definition

External quantum efficiency (EQE) refers to the ratio of the number of photons emitted by an optical source, such as a laser or LED, to the number of charge carriers (electrons or holes) that recombine to produce those photons. This measure is crucial because it indicates how effectively an optical source converts electrical energy into light, impacting its overall performance and applications.

5 Must Know Facts For Your Next Test

1. External quantum efficiency is influenced by factors like material quality, design, and temperature, affecting how much light is produced from electrical input.
2. In practical applications, EQE values can be significantly lower than internal quantum efficiency due to non-radiative recombination processes and light escape.
3. A higher EQE value indicates a more efficient optical source, which is desirable for applications like solid-state lighting and communication systems.
4. Improving EQE is a key focus in research for enhancing the performance of lasers and LEDs, leading to innovations in optoelectronic devices.
5. EQE is often represented as a percentage, with values typically ranging from a few percent up to over 90% in advanced devices.

Review Questions

• How does external quantum efficiency impact the performance of optical sources like lasers and LEDs?
  • External quantum efficiency directly impacts the brightness and energy consumption of optical sources. A higher EQE means that more photons are emitted per charge carrier recombination, leading to brighter light output with less electrical input. This is particularly important in applications where energy efficiency is critical, such as in solid-state lighting and high-speed communication systems.
• Compare external quantum efficiency with internal quantum efficiency and discuss their significance in the design of optical sources.
  • External quantum efficiency measures how many photons are emitted externally relative to charge carriers recombining, while internal quantum efficiency focuses on the recombination process itself. Both metrics are crucial for assessing device performance. Internal quantum efficiency gives insight into material properties and charge dynamics, while external quantum efficiency indicates how well a device performs in practical applications, including real-world light output.
• Evaluate the role of material quality and design improvements in enhancing the external quantum efficiency of optical sources.
  • Material quality significantly influences external quantum efficiency, as defects can lead to non-radiative recombination losses. Design improvements, such as optimizing layer thickness and incorporating light extraction techniques, help mitigate these losses. By focusing on better materials and innovative designs, researchers can achieve higher EQE values, which enhances the effectiveness and applicability of lasers and LEDs in various fields.

Related terms

Internal Quantum Efficiency: The measure of how effectively charge carriers in a device recombine to produce photons, without accounting for losses due to escape or non-radiative processes.

Radiative Recombination: A process where an electron and hole combine, resulting in the emission of a photon, which is key for generating light in LEDs and lasers.

Light Emitting Diode (LED): A semiconductor device that emits light when an electric current passes through it, utilizing the principles of electroluminescence and quantum efficiency.