AlN Bulk Crystal Growth by Physical Vapor Transport

Dalmau, Rafael; Sitar, Zlatko

doi:10.1007/978-3-540-74761-1_24

Cited by 26 publications

(18 citation statements)

References 74 publications

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“…The orientation relation between the AlN film and SiC substrate can be summarized as (0002) AlN //(0006) SiC and [10–10] AlN //[10–10] SiC . Oxygen and carbon are two common contaminants that tend to be incorporated in AlN crystals, and their concentrations are typically around 10 19 atom/cm 3 in AlN crystals fabricated using commercial AlN powder . In this study, quantitative SIMS analysis revealed that the concentrations of oxygen and carbon in the as‐grown AlN crystals were 4 × 10 20 and 3 × 10 20 atom/cm 3 , respectively.…”

Section: Resultsmentioning

confidence: 58%

Growth of AlN Crystals on SiC Substrates by Thermal Nitridation of Al₂O₃

et al. 2014

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The growth of AlN crystals on c-plane 6H-SiC substrates by thermal nitridation of Al 2 O 3 pellets in the presence of graphite and ZrO 2 was demonstrated. Addition of graphite and ZrO 2 effectively accelerated the evaporation of Al 2 O 3 , yielding c-axis oriented AlN films on SiC substrates. The SiC substrate was severely deteriorated at 2173 K, which produced a porous interface between the AlN film and substrate, resulting in lowquality AlN crystals. The deterioration of SiC was successfully suppressed by introducing a pre-deposited homo-buffer layer, allowing two-dimensional-like growth of AlN. The buffer layer promoted the formation of a high-quality AlN film. At 2173 K, the full-width at half maximum of the X-ray rocking curves of the (0002) and (10-10) planes of the AlN film was 360 and 425 arcsec, respectively.A. Zangvil-contributing editor Manuscript No. 34555.

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Section: Resultsmentioning

confidence: 58%

Growth of AlN Crystals on SiC Substrates by Thermal Nitridation of Al₂O₃

et al. 2014

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“…• C. 27 However, substantial light absorption in the DUV spectrum caused by Al vacancies and substitutional impurities was observed in PVT-grown AlN crystals. Recently, hydride vapor phase epitaxy (HVPE) was employed, 28 by which a thick AlN substrate was grown on a PVT-grown AlN, demonstrating the epitaxial layers with a low threading dislocation density and high UV transmittance.…”

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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“…of carbon and 2-40 ppm wt. of silicon [6,8,13]. As they can form volatile compounds such as Al 2 O, CO, SiO, and Si and easily escape the semi-closed crucible [9,25], therefore their concentrations in the gas phase should be considerably higher.…”

Section: Origin and Composition Of The Precipitatesmentioning

confidence: 99%

“…Substrates for epitaxy cut out of such crystals are now commercially available. However, the size, quantity and structural quality are still limited due to numerous peculiarities in the crystal growth of this compound, and research regarding different hot-zone materials, growth parameters and seeding strategies is continuing [6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Precipitates originating from tungsten crucible parts in AlN bulk crystals grown by the PVT method

Langhans

Kiefer

Hartmann

et al. 2015

Crystal Research and Technology

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In order to evaluate the possible involvement of crucible materials in the growth of AlN bulk crystals grown by physical vapor transport, we applied growth conditions with a high vertical thermal gradient and hence high supersaturation of aluminum vapor. Under these conditions, precipitates formed causing diffuse grayish substructures at the initial growth interface and in the crystal body, decorating dislocations. Electron microscopy studies revealed that the precipitates are elongated, single‐phase particles with sizes of 50–500 nm of commensurate structure, oriented along the <11true2¯0> direction. Chemical analysis of the precipitates showed tungsten as well as carbon and oxygen. The lattice parameters of the precipitates are in close agreement to hexagonal tungsten hemicarbide (W2C). The possible transport from the tungsten parts and its conversion into tungsten hemicarbide precipitates is discussed. We thus conclude that the W2C precipitates may contribute to the decoration of dislocations, even in growth with moderate thermal gradients.

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AlN Bulk Crystal Growth by Physical Vapor Transport

Cited by 26 publications

References 74 publications

Growth of AlN Crystals on SiC Substrates by Thermal Nitridation of Al₂O₃

Growth of AlN Crystals on SiC Substrates by Thermal Nitridation of Al₂O₃

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

Precipitates originating from tungsten crucible parts in AlN bulk crystals grown by the PVT method

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AlN Bulk Crystal Growth by Physical Vapor Transport

Cited by 26 publications

References 74 publications

Growth of AlN Crystals on SiC Substrates by Thermal Nitridation of Al2O3

Growth of AlN Crystals on SiC Substrates by Thermal Nitridation of Al2O3

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

Precipitates originating from tungsten crucible parts in AlN bulk crystals grown by the PVT method

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Growth of AlN Crystals on SiC Substrates by Thermal Nitridation of Al₂O₃

Growth of AlN Crystals on SiC Substrates by Thermal Nitridation of Al₂O₃