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

Laubsch, A.; Sabathil, M.; Bergbauer, Werner; Straßburg, Martin; Lugauer, Hans-Juergen; Peter, M.; Lutgen, S.; Linder, N.; Streubel, K.; Hader, J.; Moloney, Jerome V.; Pasenow, B.; Koch, S. W.

doi:10.1002/pssc.200880950

Cited by 119 publications

(107 citation statements)

References 15 publications

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“…for E gap = 3.5 eV) and the corresponding coefficients cannot account for the experimentally measured values in nitride devices (10 −31 -10 −30 cm 6 s −1 ) [3][4][5][6][7][8][9][10][11]. The coefficients increase drastically for decreasing band-gap values in the range of 2.4-3.5 eV, which is the typical band-gap range for nitride devices.…”

Section: A Direct Auger Recombination In Ganmentioning

confidence: 87%

“…As a result, it becomes an important carrier recombination mechanism at high carrier densities and reduces the efficiency of solid-state light emitters at high currents. In particular, Auger recombination has been shown to be involved in the efficiency reduction of nitride LEDs and lasers at high power [2][3][4][5][6][7][8][9][10][11][12][13]. The direct Auger recombination process [ Fig.…”

Section: Introductionmentioning

confidence: 99%

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First-principles calculations of indirect Auger recombination in nitride semiconductors

et al. 2015

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Auger recombination is an important nonradiative carrier recombination mechanism in many classes of optoelectronic devices. The microscopic Auger processes can be either direct or indirect, mediated by an additional scattering mechanism such as the electron-phonon interaction and alloy disorder scattering. Indirect Auger recombination is particularly strong in nitride materials and affects the efficiency of nitride optoelectronic devices at high powers. Here, we present a first-principles computational formalism for the study of direct and indirect Auger recombination in direct-band-gap semiconductors and apply it to the case of nitride materials. We show that direct Auger recombination is weak in the nitrides and cannot account for experimental measurements. On the other hand, carrier scattering by phonons and alloy disorder enables indirect Auger processes that can explain the observed loss in devices. We analyze the dominant phonon contributions to the Auger recombination rate and the influence of temperature and strain on the values of the Auger coefficients. Auger processes assisted by charged-defect scattering are much weaker than the phonon-assisted ones for realistic defect densities and not important for the device performance. The computational formalism is general and can be applied to the calculation of the Auger coefficient in other classes of optoelectronic materials.

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Section: A Direct Auger Recombination In Ganmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

First-principles calculations of indirect Auger recombination in nitride semiconductors

et al. 2015

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“…[9][10][11][12][13][14][15] Also high pumping conditions are known to cause a further reduction of the efficiency that is attributed to Auger recombination. [16][17][18][19] In this letter, we report on an additional high excitation loss mechanism arising from confined hole continuum (CHC) states promoting carrier leakage, which is of utmost importance for the implementation of efficient LDs emitting in the green spectral region.…”

Section: Introductionmentioning

confidence: 99%

Polarization-induced confinement of continuous hole-states in highly pumped, industrial-grade, green InGaN quantum wells

Nippert

Nirschl

Schulz

et al. 2016

Journal of Applied Physics

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We investigate industrial-grade InGaN/GaN quantum wells (QWs) emitting in the green spectral region under high, resonant pumping conditions. Consequently, an ubiquitous high energy luminescence is observed that we assign to a polarization field Confined Hole Continuum (CHC). Our finding is supported by a unique combination of experimental techniques, including transmission electron microscopy, (time-resolved) photoluminescence under various excitation conditions, and electroluminescence, which confirm an extended out-of-plane localization of the CHC-states. The larger width of this localization volume surpasses the QW thickness, yielding enhanced nonradiative losses due to point defects and interfaces, whereas the energetic proximity to the bulk valence band states promotes carrier leakage. Published by AIP Publishing.

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“…This model can describe the emission characteristics of greenemitting InGaN-based LED over a wide current-density range (see Figure 2). We thus identify a high-density QW-internal Auger-like process as the culprit for the high-current losses observed, 7 with C = 3.5 × 10 −31 cm 6 /s.…”

Section: Figure 1 Internal Efficiency Of a Green-emitting Single-quamentioning

confidence: 99%

Improving the high-current efficiency of LEDs

Laubsch¹

2009

SPIE Newsroom

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Understanding the origin of efficiency losses is key to developing the ultimate solid-state light source.Indium gallium nitride (InGaN) has great potential in LEDbased applications becasue of its ability to emit in the shortwavelength region, from near-UV to green. The emitting region is deposited as a quasi-2D quantum-well (QW) heterostructure composed of InGaN and gallium nitride. The past decade has seen tremendous progress in both epitaxial (or crystaline-layer) growth and InGaN LED design.We recently demonstrated a wall-plug efficiency (i.e., the conversion of electrical to optical power as measured from the line source to the resulting emission) of about 60% for a blue ThinGaN R LED. 1 The chip-level light-extraction efficiency of such devices has reached values in excess of 80%. However, the internal quantum efficiency for light generation by electron-hole carrier recombination remains lower. Even worse, the internal efficiency usually peaks around current densities considerably below the operating current and decreases monotonously towards higher currents, a phenomenon frequently called 'droop.' Understanding and reducing droop is crucial to reach the ultimate efficiency of InGaN-based LEDs. Various mechanisms that may cause this effect have been suggested, including carrier escape, 2 losses due to dislocations, 3 and the Auger effect. 4,5 In our work, we validate that the efficiency drop at high current is QW internal. We compare temperature-and excitationpower-density-dependent resonant photoluminescence (PL) to electroluminescence (EL) using a green-emitting InGaN single-QW (SQW) LED structure. We measure PL and EL on the same ThinGaN chip. For PL excitation, a 405nm laser optically excites electron-hole pairs well below the band-gap energy of the GaN barrier. 6 This enables us to reliably isolate QW-internal losses from losses due to parasitic carrier recombination outside the QW. Our experimental data strongly supports QW-internal loss. Figure 1. Internal efficiency of a green-emitting single-quantum-well (SQW) LED measured by electroluminescence (EL, empty boxes) compared to that measured in a resonant-photoluminescence (PL) experiment (solid boxes). Both experiments were performed at 300 (black) and 4K (red). Carrier generation and recombination in EL and PL are shown schematically in the conduction-and valence-band (CB/VB) diagrams in the insets. a.u.: Arbitrary units.All significant trends of the EL efficiency are followed perfectly by the resonant-PL efficiency (see Figure 1).We can reproduce the dependence of the internal efficiency on current density, J, using a simple rate-equation model of the form J ∼ A × n + B × n 2 + C × n 3 , where n is the QW carrier density and A, B, and C are coefficients for nonradiative, radiative, and (nonradiative) Auger-like recombination, respectively. This model can describe the emission characteristics of greenemitting InGaN-based LED over a wide current-density range (see Figure 2). We thus identify a high-density QW-internal Auger-like process as the culpri...

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

Cited by 119 publications

References 15 publications

First-principles calculations of indirect Auger recombination in nitride semiconductors

First-principles calculations of indirect Auger recombination in nitride semiconductors

Polarization-induced confinement of continuous hole-states in highly pumped, industrial-grade, green InGaN quantum wells

Improving the high-current efficiency of LEDs

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