Light extraction technologies for high-efficiency GaInN-LED devices

Sabathil

Bergbauer

et al. 2009

119

We identify a quantum well internal high density Augerlike loss process as the origin of the so called ‘droop’ of internal quantum efficiency (IQE) in InGaN based light emitters. The IQE of such a device peaks at small current densities and then monotonously decreases towards higher currents. The origin of this ‘droop’ has been widely discussed recently and many possible mechanisms have been proposed for explaining the effect. We compare temperature and carrier density dependent electroluminescence and photoluminescence measurements of a green emitting single quantum‐well (SQW) LED over a wide parameter range. The carrier‐density as well as temperature dependence of efficiency is identical in both measurements, indicating that the decrease is due to a high density quantum‐well internal loss process. The data can be accurately modeled assuming an Auger‐like loss process with C = 3.5 × 10–31 cm6s–1. We suggest phonon‐ or defect‐assisted Auger recombination as the origin of this loss‐channel. The high current performance can be improved if a thick InGaN SQW or a multi quantum‐well (MQW) is used. This is in very good agreement with theoretical simulations (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Section: Methodsmentioning

confidence: 99%

On the origin of IQE‐‘droop’ in InGaN LEDs

Sabathil

Bergbauer

et al. 2009

119

“…The light extraction efficiency of ThinGaN TM -chips reaches up to 75% and the technology provides excellent chip size scalability [1,2]. The overall brightness of green LEDs was increased by optimizing the Multi-Quantum Well (MQW) emission.…”

Section: Methodsmentioning

confidence: 99%

Green ThinGaN power‐LED demonstrates 100 lm

Peter¹,

Stauß

et al. 2008

Recent progress in the epitaxy of InGaN LEDs leads to a significant improvement of output power for green LEDs: 100 lm at 350 mA and 189 lm at 1 A are demonstrated for a 1 mm2 ThinGaN Chip at 531 nm, mounted in an OSRAM Dragon package with spherical silicone lens and OSRAM Argus lens. The chip is especially designed for low current applications like LCD backlighting where high efficiencies are needed. Efficacies of 123 lm/W at 100 mA and 80 lm/W at 350 mA have been achieved with this LED. The Influence of Multi Quantum Well emission on LED brightness was investigated in respect of driving current and temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

“…Standard LEDs with a chip size of 290 · 290 μm 2 have been fabricated. ThinGaN-chips reach light extraction efficiencies beyond 80%, and the technology provides excellent chip size scalability [1], [11]. Electroluminescence (EL) was measured in DC-operation for small current densities up to 1 Acm −2 , and with 400 ns pulses (0.8% duty cycle) above this current density to avoid heating of the device.…”

Section: Methodsmentioning

confidence: 99%

Luminescence properties of thick InGaN quantum‐wells

Bergbauer

Sabathil

et al. 2009

Self Cite

In this paper, we discuss the physics of recombination in thick InGaN quantum-well (QW) based structures. Thick InGaN QWs have been suggested as one concept to reduce the typical decrease of internal efficiency of InGaN based light emitters towards high current densities. We show that at typical operation current densities, recombination in such thick QWs mainly originates from excited QW-states, which exhibit good electron hole overlap and large spatial extent, enabling a reduction of carrier density. We identify these states by comparing current dependent electroluminescence spectra to band structure simulations. The reduction of carrier density is verified by measuring current dependent carrier lifetimes. We find that saturation of efficiency is reduced for increasedQWthickness. However, the same effect can also be achieved using an MQW structure optimized for real MQW emission. We conclude that regardless of the employed concept, a decrease in carrier density is central to improve the high current efficiency of InGaN based light emitters