High Brightness Blue InGaN/GaN Light Emitting Diode on Nonpolar m-plane Bulk GaN Substrate

Iso, Kenji; Yamada, Hisashi; Hirasawa, Hirohiko; Fellows, Natalie; Saitô, Makoto; Fujito, Kenji; DenBaars, Steven P.; Speck, James S.; Nakamura, Shuji

doi:10.1143/jjap.46.l960

Cited by 95 publications

(68 citation statements)

References 20 publications

(21 reference statements)

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“…1, the major advantage of thick InGaN SQWs is the drastically reduced carrier density. In contrast, the piezoelectric fields are of minor importance, consistent with results published by Iso et al [14]. These authors observe for a non-polar m-plane grown LED structure, i.e.…”

Section: Resultssupporting

confidence: 90%

Luminescence properties of thick InGaN quantum‐wells

Laubsch

Bergbauer

Sabathil

et al. 2009

Phys. Status Solidi (c)

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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

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Section: Resultssupporting

confidence: 90%

Luminescence properties of thick InGaN quantum‐wells

Laubsch

Bergbauer

Sabathil

et al. 2009

Phys. Status Solidi (c)

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“…[7,8] Recently, dramatic improvements in a-plane and m-plane LED performance have been reported for bulk a-plane and m-plane GaN substrates with low TDD in the 10 6 cm À2 range. [9][10][11][12] These results confirm that a low-dislocation-density material is necessary for high efficiency nonpolar nitride LEDs. Unfortunately, the size, availability, and cost of nonpolar freestanding bulk GaN substrates are serious barriers to the development and adoption of inexpensive nonpolar LEDs.…”

supporting

confidence: 61%

Nanowire‐Templated Lateral Epitaxial Growth of Low‐Dislocation Density Nonpolar a‐Plane GaN on r‐Plane Sapphire

Lin

Creighton

et al. 2009

Advanced Materials

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Blue-and green-light-emitting diodes (LEDs) based on InGaN/ GaN films that are typically grown along the polar c-axis suffer from strong polarization-related internal electric fields that limit the radiative recombination efficiency due to spatial separation of holes and electrons. [1,2] LEDs based on nonpolar GaN orientations, including the (1100) m-plane and (1120) a-plane, are free from polarization-related internal electric fields, and thus have the potential for improved efficiencies.[2] Accordingly, research efforts in developing nonpolar InGaN/GaN LEDs have dramatically increased recently. However, a major problem for the development and adoption of efficient nonpolar LEDs is the limited availability of high-quality substrates. Growth of nonpolar a-plane GaN epilayers using nucleation-layer techniques results in films with high threading dislocation densities (TDDs) in the mid-high 10 10 cm À2 range, and basal-plane stacking-fault densities in the mid-high 10 5 cm À1 range. [3][4][5][6] The presence of high levels of extended defects, particularly threading dislocations, leads to lower device lifetimes and reduced efficiencies and output powers. [7,8] Recently, dramatic improvements in a-plane and m-plane LED performance have been reported for bulk a-plane and m-plane GaN substrates with low TDD in the 10 6 cm À2 range. [9][10][11][12] These results confirm that a low-dislocation-density material is necessary for high efficiency nonpolar nitride LEDs. Unfortunately, the size, availability, and cost of nonpolar freestanding bulk GaN substrates are serious barriers to the development and adoption of inexpensive nonpolar LEDs. While the size, cost, and availability of bulk freestanding GaN substrates are likely to continue to improve in the future, the cost is unlikely to come close to that of sapphire substrates for the foreseeable future, rendering them impractical for inexpensive devices such as LEDs. Epitaxial lateral overgrowth (ELO) techniques and variations of ELO have recently been employed to produce nonpolar a-plane [13][14][15] and m-plane [16,17] GaN films with TDD in the 10 6 -10 8 cm À2 range in the wing regions. However, given the process complexity, and hence high cost, of ELO-based buffers, the use of ELO is also likely to be restricted to more expensive devices, such as laser diodes, for the foreseeable future.In order to enable the development and adoption of nonpolar LEDs for general illumination, we propose and demonstrate here a novel technique known as nanowire-templated lateral epitaxial growth, or NTLEG. In the NTLEG technique, vertical GaN nanowire arrays serve as strain-relief templates for the lateral growth and nucleation of low-dislocation-density GaN. The NTLEG process is illustrated in Figure 1. An array of vertically aligned, dislocation-free GaN nanowires is first epitaxially grown on a substrate by metal-catalyzed vapor-liquid-solid (VLS) growth. [18][19][20] Following growth of the aligned nanowire array, the growth conditions are changed, in situ and without the need to re...

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“…high polarisation fields caused by the increasing strain with higher InN mole fractions. Possible mechanisms of 'efficiency droop' that have been proposed include Auger recombination [52,56], high defect density [54,58], carrier leakage [59], polarisation-induced built-in electric fields at hetero-interfaces [60,61], poor p-type conductivity [62,63] and carrier delocalisation at high current densities [64]. In order to reduce the current density and thus the efficiency droop, a thicker single quantum well has been proposed to replace thin multiple quantum wells as the active region [12].…”

Section: Green Gap and Efficiency Droopmentioning

confidence: 99%