Thermophysical Characterization of Efficiency Droop in GaN-Based Light-Emitting Diodes.

Tzer-En Nee,Jui-Ju Hsiao,Bo-Yan Zhong,Jen-Cheng Wang,Ya-Fen Wu

doi:10.3390/nano11061449

Abstract

An efficiency droop in GaN-based light-emitting diodes (LED) was characterized by examining its general thermophysical parameters. An effective suppression of emission degradation afforded by the introduction of InGaN/GaN heterobarrier structures in the active region was attributable to an increase in the capture cross-section ratios. The Debye temperatures and the electron–phonon interaction coupling coefficients were obtained from temperature-dependent current-voltage measurements of InGaN/GaN multiple-quantum-well LEDs over a temperature range from 20 to 300 K. It was found that the Debye temperature of the LEDs was modulated by the InN molar fraction in the heterobarriers. As far as the phonons involved in the electron–phonon scattering process are concerned, the average number of phonons decreases with the Debye temperature, and the electron–phonon interaction coupling coefficients phenomenologically reflect the nonradiative transition rates. We can use the characteristic ratio of the Debye temperature to the coupling coefficient (DCR) to assess the efficiency droop phenomenon. Our investigation showed that DCR is correlated to quantum efficiency (QE). The light emission results exhibited the high and low QEs to be represented by the high and low DCRs associated with low and high injection currents, respectively. The DCR can be envisioned as a thermophysical marker of LED performance, not only for efficiency droop characterization but also for heterodevice structure optimization.

Highlights

The increasing demand for lighting for a variety of applications such as bicycle headlights, advanced electronic displays, traffic lights, and indoor/outdoor lighting is driving the development of high-brightness nitride semiconductor light-emitting devices (LEDs), but a critical issue which remains to be resolved is the suppression of efficiency droop at high current injection levels [1,2]
The results reveal that the figure of merit affecting the LED
In an attempt to experimentally demonstrate the correlation of the characteristic ratio of the Debye temperature to the electron–phonon interaction coupling and quantum efficiency, we examined the capture cross-section ratios from high to low, corresponding to the suppression ability of emission degradation for samples prepared by the introduction of the well-designed InGaN/GaN multi-quantum barrier (MQB) heterostructures in the quantum-well transition zone

Summary

Introduction

The increasing demand for lighting for a variety of applications such as bicycle headlights, advanced electronic displays, traffic lights, and indoor/outdoor lighting is driving the development of high-brightness nitride semiconductor light-emitting devices (LEDs), but a critical issue which remains to be resolved is the suppression of efficiency droop at high current injection levels [1,2]. Investigators have devised many ways to improve device quantum efficiency. A profound improvement in the light output power of LEDs has been obtained owing to a reduction in the threading dislocation density in the InGaN/AlInGaN multiple quantum well (MQW) active region by employing a sputtered AlN nucleation layer (NL) instead of an AlGaN NL [3]. An increase in the luminous intensity of LEDs fabricated on carbon nanotube-patterned sapphire substrates has been observed as a result of the rapid relaxation of strain in the grown GaN thin film [4]. With the use of self-organized InGaN/AlGaN dot-in-a-wire core-shell nanowire arrays, a new type of axial nanowire LED heterostructure has been fabricated with a several orders of magnitude enhancement of luminescence emission [5]. Similar observations have been made for well-designed multi-quantum barrier (MQB) LEDs, which exhibit a higher quantum efficiency, as well as a higher temperature insensitivity, than conventional

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