263 nm wavelength UV-C LED on face-to-face annealed sputter-deposited AlN with low screw- and mixed-type dislocation densities

Uesugi, Kenjiro; Kuboya, Shigeyuki; Shojiki, Kanako; Xiao, Shengqiang; Nakamura, Toshio; Kubo, Masataka; Miyake, Hideto

doi:10.35848/1882-0786/ac66c2

Cited by 27 publications

(15 citation statements)

References 34 publications

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“…Moreover, a recent finding proposes that HTA-sputtered AlN templates can improve the surface flatness of overgrown AlGaN. [12] For nonpseudomorphic growth, this comprises a rough growth starts on the HTA template, leading to a relatively high AlGaN layer thickness of several micrometers to reach coalescence and a smooth surface. [13][14][15] Inclination of edge-type TDs perpendicular to the growth direction has been suggested as a route for strain relaxation and dislocation reduction in AlGaN, [16][17][18][19] as well as in AlN, [20] provided there is a sufficient number of TDs available.…”

Section: Doi: 101002/pssa202300083mentioning

confidence: 99%

Role of Oxygen Incorporation in High Temperature Annealed AlGaN

Zainal

Hagedorn

Netzel

et al. 2023

Physica Status Solidi (a)

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Aluminum gallium nitride (AlGaN) based ultraviolet light emitting diodes (UV LEDs) have a variety of applications in areas of biological sensing/detection, optical data communication, medical treatments, and sterilization. However, it is challenging to increase the efficiency of UV LEDs emitting in the UVB and UVC spectral range. [1] One of the approaches to achieve this goal is to develop AlGaN-based UV LEDs on low threading dislocation density (TDD) AlGaN layers.For UV LEDs, AlGaN layers with an Al mole fraction x Al above 0.5 are required to avoid absorption of the UV light generated in the active region of the LEDs. [2][3][4][5] However, it is challenging to reduce the TDD in AlGaN layers. Without improvements in the growth and fabrication process, relaxed or partially relaxed AlGaN layers with x Al > 0.5 usually exhibit a TDD of more than mid-10 9 cm À2 . [6] This is associated with the lattice mismatch between AlGaN and AlN that becomes larger with increasing Ga content. Moreover, relaxation of the AlGaN when growing the layers above the Matthews-Blakeslee critical thickness can lead to surface roughening [7] and generation of new dislocations. [8] Low dislocation density AlGaN layers with the absence of relaxation can be obtained by pseudomorphic growth of the layers on bulk AlN substrates. Nonetheless, pseudomorphic growth is limited by x Al and layer thickness as reported by. [8] For example, pseudomorphic growth of n-Al 0.6 Ga 0.4 N can be achieved with a thickness of up to 0.5 μm, while for n-Al 0.7 Ga 0.3 N, the thickness is up to 1.0 μm. Dalmau et al. found that a 0.4 μm thick Al 0.65 Ga 0.35 N layer already shows 8% of relaxation. [9] In a recent work, [10] pseudomorphic growth was demonstrated for thicker Al 0.6 Ga 0.4 N layers with thicknesses between 0.95 and 3.5 μm. However, these layers suffered from high compressive stress of 3-4 GPa, which could lead to detrimental relaxation in subsequently grown layers with higher Ga content (x Al < 0.6) and huge wafer bow. The latter results in non-uniform growth of the active region of devices and problems in the LED chip process. In the same report, [10] the authors attempted to relieve the stress in the layers by introducing two types of buffer layers, that is, with continuously graded composition and stepwise changed composition, neither of which was successful. From this result, a large barrier for the nucleation of misfit dislocation segments in Al-rich AlGaN layers was concluded. Hence, AlGaN strain relaxation on AlN is challenging especially when growing on low dislocation density AlN buffer layers.At present, UV-transparent bulk AlN substrates are expensive and their availability is still limited. Therefore, AlGaN layers are widely grown on AlN/sapphire templates. A thick fully strained Al 0.8 Ga 0.2 N layer with a TDD of %5 Â 10 8 cm À2 was obtained by growing the layer on maskless epitaxial lateral overgrowth (ELO) AlN/sapphire template. [6,11] In contrast, the TDD was higher

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Section: Doi: 101002/pssa202300083mentioning

confidence: 99%

Role of Oxygen Incorporation in High Temperature Annealed AlGaN

Zainal

Hagedorn

Netzel

et al. 2023

Physica Status Solidi (a)

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“…[17][18][19][20] For example, at present, high-quality c-oriented AlN lms on sapphire substrates prepared by the HTA method have played an important role in promoting the performance of DUV light-emitting diodes. [21][22][23][24][25] The method of fabricating high-quality c-oriented AlN/ sapphire by HAT was rst reported by H. Miyake et al, subsequently followed by researchers all over the world. 16,18,20,25 The coriented AlN/sapphire for annealing can be obtained by metalorganic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), or sputtering.…”

Section: Introductionmentioning

confidence: 99%

The AlN lattice-polarity inversion in a high-temperature-annealed c-oriented AlN/sapphire originated from the diffusion of Al and O atoms from sapphire

Jiang,

Ben,

Sun

et al. 2024

Nanoscale Adv.

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“… 18 , 19 Consequently, DUV LEDs fabricated on FFA Sp-AlN achieved an external quantum efficiency (EQE) of 8.0% at 263 nm, a wavelength with a high bactericidal effect. 20 An attempt to fabricate FFA Sp-AlN templates in combination with nanopatterned sapphire substrates (NPSS) has also been reported. 21 , 22 Since NPSS can prevent cracks by strain relaxation and improve the light extraction efficiency, 22 – 26 improved EQE is expected when NPSS are implemented in AlGaN DUV LEDs using FFA Sp-AlN.…”

Section: Introductionmentioning

confidence: 99%

Micro- and Nanostructure Analysis of Vapor-Phase-Grown AlN on Face-to-Face Annealed Sputtered AlN/Nanopatterned Sapphire Substrate Templates

Nakanishi

Hayashi

Hamachi

et al. 2023

J. Electron. Mater.

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Micro- and nanostructures in vapor-phase-grown AlN on face-to-face annealed sputtered AlN (FFA Sp-AlN) templates formed on nanopatterned sapphire substrates (NPSS) were comprehensively analyzed using transmission electron microscopy. The comparison between metal–organic vapor-phase epitaxy-grown AlN/FFA Sp-AlN/hole-type NPSS (Sample MOH) and hydride vapor-phase epitaxy-grown AlN/FFA Sp-AlN/cone-type NPSS (Sample HVC) showed apparent differences in the morphology of dislocation propagation, presence of voids, shape of polarity inversion boundaries, and crystal structure on the slope region of NPSS. Notably, cross-sectional and plan-view observations revealed that the quality of FFA Sp-AlN significantly affects the threading dislocation density in the vapor-phase-grown layer. At the slope region of the AlN/NPSS interface, γ -AlON was observed in the MOH sample, while highly misaligned AlN grains were observed in the HVC sample. These characteristic crystal structures affect the occurrence of dislocations via different mechanisms in each sample. This study provides practical information for strategically controlling the micro- and nanostructures formed in AlN/NPSS structures for high-performance AlGaN-based deep-ultraviolet emitters. Supplementary Information The online version contains supplementary material available at 10.1007/s11664-023-10348-3.

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263 nm wavelength UV-C LED on face-to-face annealed sputter-deposited AlN with low screw- and mixed-type dislocation densities

Cited by 27 publications

References 34 publications

Role of Oxygen Incorporation in High Temperature Annealed AlGaN

Role of Oxygen Incorporation in High Temperature Annealed AlGaN

The AlN lattice-polarity inversion in a high-temperature-annealed c-oriented AlN/sapphire originated from the diffusion of Al and O atoms from sapphire

Micro- and Nanostructure Analysis of Vapor-Phase-Grown AlN on Face-to-Face Annealed Sputtered AlN/Nanopatterned Sapphire Substrate Templates

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