# Active Region Part A. Internal Quantum Efficiency in LEDs

## Abstract

In this chapter, we present different techniques used to assess the internal quantum efficiency (IQE) in light emitting diodes (LEDs). The commonly used technique based on temperature-dependent photoluminescence relies in strong assumptions which are discussed in this chapter. We introduce an alternative method to determine IQE based on electroluminescence, in which the external quantum efficiency (EQE) is measured from a single facet of the LED, where the light emission can be calculated with good accuracy. The IQE is ultimately obtained from the ratio of the EQE and the calculated light extraction efficiency. We develop an optical model of the light emission in a multilayered LED structure, from which we derive and validate an approximate model to easily calculate the extraction efficiency through the top facet of any LED structure. We address the various assumptions made to calculate the direct emission model through a single facet and evaluate the effect of photon recycling in the quantum wells. We also calculate the sensitivity of the model to the LED parameters and surface roughness. Finally, we apply this technique to calculate the IQE of both a state-of-the-art and a low performance GaN-based LEDs, highlighting the particular features in each structure.

## Keywords

Extraction Efficiency Sapphire Substrate External Quantum Efficiency Lead Structure Carbon Black Particle## Notes

### Acknowledgements

The authors would like to thank James Speck for triggering this work, for his continuous interest and many enlightened discussions and Amorette Getty for her large contribution with the experimental part in this work. This material is based upon work partially supported as part of the ‘Center for Energy Efficient Materials’ at UCSB, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001009 and by the Department of Energy (DOE) under project No. DE-FC26-06NT42857 and by the Solid State Lighting and Energy Center (SSLEC) at the University of California, Santa Barbara (UCSB).

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