Control of Dislocations and Stress in AlGaN on Sapphire Using a Low Temperature Interlayer

Amano, H.; Iwaya, Motoaki; Hayashi, Nobuaki; Kashima, Takayuki; Nitta, Shugo; Wetzel, Christian; Akasaki, Isamu

doi:10.1002/(sici)1521-3951(199911)216:1<683::aid-pssb683>3.0.co;2-4

Cited by 85 publications

(38 citation statements)

References 7 publications

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“…10 Several groups reported on different approaches to grow thick AlGaN layers over GaN buffers. 11,12 However, the use of GaN layers drastically decreases the light extraction efficiency in deep-UV emitters due to strong absorption. We now report an approach of using a set of AlN/AlGaN superlattices ͑SLs͒ to reduce the biaxial tensile strain and successfully grow 3.0-m-thick Al 0.2 Ga 0.8 N on sapphire without any cracks.…”

mentioning

confidence: 99%

Crack-free thick AlGaN grown on sapphire using AlN/AlGaN superlattices for strain management

Zhang

Wang

Gaevski

et al. 2002

Applied Physics Letters

197

105

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We report on an AlN/AlGaN superlattice approach to grow high-Al-content thick n+-AlGaN layers over c-plane sapphire substrates. Insertion of a set of AlN/AlGaN superlattices is shown to significantly reduce the biaxial tensile strain, thereby resulting in 3-μm-thick, crack-free Al0.2Ga0.8N layers. These high-quality, low-sheet-resistive layers are of key importance to avoid current crowding in quaternary AlInGaN multiple-quantum-well deep-ultraviolet light-emitting diodes over sapphire substrates.

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mentioning

confidence: 99%

Crack-free thick AlGaN grown on sapphire using AlN/AlGaN superlattices for strain management

Zhang

Wang

Gaevski

et al. 2002

Applied Physics Letters

197

105

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“…SEM analysis revealed, that the cracked surface consisted of pieces of AlGaN crystals of about 10 mm in size. Amano et al [5] experimentally showed, that a thin low-temperature ($500 C) AlN interlayer reduced stress in the AlGaN layer, preventing crack generation in the AlGaN films. The present results indicate, that thin HT-AlN also significantly reduces the tensile stress in the AlGaN layer and is useful to grow crack-free high quality AlGaN films.…”

Section: Resultsmentioning

confidence: 99%

Cathodoluminescence and Al Composition of Biaxially Stressed AlGaN/GaN Epitaxial Layers

Lee¹,

Park²

2002

phys. stat. sol. (a)

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We report on the cathodoluminescence (CL) of Al0.25Ga0.75N (x = 0.25) and underlying GaN films and on the Al composition of the AlGaN with the biaxial residual stress taken into account. Crack‐free thick AlGaN layers were fabricated by introducing a thin AlN interlayer on a high quality GaN epitaxial layer. The CL band‐edge emission of AlGaN from a non‐cracked region appeared at a lower energy than that from the cracked region. This is the direct indication, that crack relaxes biaxial tensile stress in AlGaN layers. When the Al composition x was lower than 0.5, the Al compositions measured by X‐ray diffraction fell between the values estimated by Vegard's law and the values of pseudomorphic assumption due to partially relaxed residual stress in the AlGaN films. When x > 0.5, they are in agreement with Vegard's law, indicating that the AlGaN layer is fully relaxed.

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“…15 It was found that the LT interlayer was effective in redefining the in-plane lattice parameter through strain relaxation. 16,17 However, it was also observed that the LT nucleation layer was less effective for the growth of highquality AlGaN than for GaN. 18 Unlike trimethylgallium (TMGa) used in GaN growth, trimethylaluminum (TMAl) used in AlGaN growth has a much stronger pre-reaction with ammonia (NH 3 ) and Al atoms do not have enough time to move to energetically favorable lattice sites due to their low surface mobility.…”

Section: Growth Of High-crystal-quality Algan Epilayersmentioning

confidence: 99%

Review—Group III-Nitride-Based Ultraviolet Light-Emitting Diodes: Ways of Increasing External Quantum Efficiency

Park

Kim

Cho

et al. 2017

ECS J. Solid State Sci. Technol.

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There is a rapidly growing demand for highly efficient ultraviolet (UV) light sources for a wide variety of applications. In particular, state-of-the-art AlGaN deep UV light-emitting diodes (DUV LEDs) exhibit inadequately low external quantum efficiencies (EQEs). The low efficiencies are attributed to the inherent material properties of high-Al-content AlGaN including strained epitaxial layers, low carrier concentrations, and strong transverse magnetic (TM)-polarized light emission. Extensive efforts have been made to tackle these challenging issues and technological developments have been achieved and enabled the fabrication of reasonable EQE LEDs. In this review, recent advances in the growth of high-quality AlGaN epitaxial layers, transparent and reflective ohmic contacts, and light extraction for AlGaN-based UV LEDs are reviewed. Al x Ga 1-x N-based ultraviolet light-emitting diodes (UV LEDs) are of technological importance because of their applications in numerous areas such as water purification, biological analysis, sensing, epoxy curing, high-density optical storage, white light illumination, UV adhesives, 3-dimensional (3D) printer and UV-coating.1,2 These applications are made possible because of their wide bandgap energy range in the UV spectrum, which spans from 6.2 eV (AlN) to 3.4 eV (GaN), namely, from UV-A (320-400 nm), UV-B (290-320 nm) to UV-C (200-290 nm).3-7 The external quantum efficiency (EQE) of Al x Ga 1-x N-based UV LEDs decreases rapidly as the molar fraction (x) of Al increases, namely, as the wavelength decreases, as illustrated in Figure 1. 8 Thus, a great deal of effort has been made in order to improve the EQE of UV LEDs. The effort notwithstanding, however, the EQE of AlGaN-based UV LEDs is still insufficiently low. The typical EQE of UV LEDs, specifically in the UV-C spectral range (100-280 nm), is less than 5% and decreases down to 10 -6 % for 210-nm AlN-based UV LEDs. 4 These low EQEs are associated with the intrinsic material properties of Al x Ga 1-x N.1,2 Figure 2 exhibits a schematic diagram of a typical AlGaN UV LED structure grown on a sapphire substrate. The structure consists of a Si-doped n-type AlGaN, an Al x Ga 1-x N/Al y Ga 1-y N multiple-quantum well (MQW) active region, an AlGaN-based electron-blocking layer (EBL), a Mg-doped p-type AlGaN, and a Mg-doped p-type GaN. Almost every layer in the structure poses different technical issues, which limit the efficiency of UV LEDs, as shown in Figure 2. First, increasing the Al content generally results in a poor crystallinity of AlGaN epilayers, causing a poor internal quantum efficiency (IQE). Second, both n-type and ptype doping efficiencies of AlGaN are difficult to increase because the ionization energies of acceptor (Mg) and donor (Si) dopants largely increase with increasing Al content. The low doping efficiency causes several technological problems: (i) a poor electrical efficiency (EE) attributable to high-resistance contacts on resistive n-type and p-type AlGaN; (ii) current crowding causing non-uniform current in...

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Control of Dislocations and Stress in AlGaN on Sapphire Using a Low Temperature Interlayer

Cited by 85 publications

References 7 publications

Crack-free thick AlGaN grown on sapphire using AlN/AlGaN superlattices for strain management

Crack-free thick AlGaN grown on sapphire using AlN/AlGaN superlattices for strain management

Cathodoluminescence and Al Composition of Biaxially Stressed AlGaN/GaN Epitaxial Layers

Review—Group III-Nitride-Based Ultraviolet Light-Emitting Diodes: Ways of Increasing External Quantum Efficiency

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