Thermal and efficiency droop in InGaN/GaN light-emitting diodes: decoupling multiphysics effects using temperature-dependent RF measurements

Arman Rashidi,Daniel Feezell,Andrew Aragon,Morteza Monavarian

doi:10.1038/s41598-019-56390-2

Abstract

Multiphysics processes such as recombination dynamics in the active region, carrier injection and transport, and internal heating may contribute to thermal and efficiency droop in InGaN/GaN light-emitting diodes (LEDs). However, an unambiguous methodology and characterization technique to decouple these processes under electrical injection and determine their individual roles in droop phenomena is lacking. In this work, we investigate thermal and efficiency droop in electrically injected single-quantum-well InGaN/GaN LEDs by decoupling the inherent radiative efficiency, injection efficiency, carrier transport, and thermal effects using a comprehensive rate equation approach and a temperature-dependent pulsed-RF measurement technique. Determination of the inherent recombination rates in the quantum well confirms efficiency droop at high current densities is caused by a combination of strong non-radiative recombination (with temperature dependence consistent with indirect Auger) and saturation of the radiative rate. The overall reduction of efficiency at elevated temperatures (thermal droop) results from carriers shifting from the radiative process to the non-radiative processes. The rate equation approach and temperature-dependent pulsed-RF measurement technique unambiguously gives access to the true recombination dynamics in the QW and is a useful methodology to study efficiency issues in III-nitride LEDs.

Highlights

Multiphysics processes such as recombination dynamics in the active region, carrier injection and transport, and internal heating may contribute to thermal and efficiency droop in InGaN/GaN lightemitting diodes (LEDs)
Previous RF measurements were performed under continuous-wave (CW) operation, where heat generated in the active region is not independently controlled, affecting the carrier dynamics of the LED and obscuring the fundamental recombination processes
Decoupling of the inherent radiative efficiency, injection efficiency, carrier recombination lifetime, carrier transport, and thermal effects under electrical injection is essential to create a complete picture of the physics associated with thermal and efficiency droop

Summary

Introduction

Multiphysics processes such as recombination dynamics in the active region, carrier injection and transport, and internal heating may contribute to thermal and efficiency droop in InGaN/GaN lightemitting diodes (LEDs). We investigate thermal and efficiency droop in electrically injected single-quantum-well InGaN/GaN LEDs by decoupling the inherent radiative efficiency, injection efficiency, carrier transport, and thermal effects using a comprehensive rate equation approach and a temperature-dependent pulsed-RF measurement technique. We used a rate equation approach and RF measurement technique to decouple the injection and transport effects from the inherent carrier dynamics in the QW, resulting in the extraction of the true differential carrier lifetime (DLT)[22,23]. We have reported on a comprehensive rate equation approach and electrically injected RF measurement technique to extract the carrier recombination lifetime and injection efficiency in III-nitride LEDs22,23. The rate equation approach and pulsed-RF measurement technique yields the inherent radiative and non-radiative recombination rates by excluding the injection, transport, and thermal effects from the carrier dynamics in the QW of InGaN/GaN LEDs

Methods

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Discussion

Conclusion