Improvement of Light Extraction Efficiency for AlGaN-Based Deep Ultraviolet Light-Emitting Diodes

Inazu, Tetsuhiko; Fukahori, Shinya; Pernot, Cyril; Kim, Myung Hee; Fujita, Takehiko; Nagasawa, Yosuke; Hirano, Akira; Ippommatsu, Masamichi; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Yamaguchi, M.; Honda, Yoshio; Amano, Hiroshi; Akasaki, Isamu

doi:10.7567/jjap.50.122101

Cited by 50 publications

(27 citation statements)

References 11 publications

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“…[1][2][3][4][5][6][7][8][9][10] The demand on UV light emission, mainly for water purification purposes, 11 pushes the research on light emitting diodes (LEDs) and laser diodes (LDs) operating at short wavelengths around 270 nm. In contrast to generic LEDs, where light is emitted perpendicular to the substrate, LDs typically are edge emitters due to the cavity produced by cleaving perpendicular to the surface and quantum well plane.…”

Section: Introductionmentioning

confidence: 99%

“…In contrast to generic LEDs, where light is emitted perpendicular to the substrate, LDs typically are edge emitters due to the cavity produced by cleaving perpendicular to the surface and quantum well plane. LEDs are typically grown heteroepitaxially on UV transparent sapphire [4][5][6][7][8] or on AlN single crystals, 9,10 which have to be thinned to avoid substrate reabsorption. Optically pumped laser structures on AlN 1-3 predominantly show TE polarized emission, where the electric field vector is perpendicular to the c axis of the wurtzite crystal.…”

Section: Introductionmentioning

confidence: 99%

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Composition dependent valence band order in c-oriented wurtzite AlGaN layers

Neuschl

Helbing

Knab

et al. 2014

Journal of Applied Physics

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Extremely weak surface emission from (0001) c -plane AlGaN multiple quantum well structure in deep-ultraviolet spectral region Valence-band splitting and band-gap reduction in ordered GaInAs/InPThe valence band order of polar wurtzite aluminum gallium nitride (AlGaN) layers is analyzed for a dense series of samples, grown heteroepitaxially on sapphire substrates, covering the complete composition range. The excitonic transition energies, found by temperature dependent photoluminescence (PL) spectroscopy, were corrected to the unstrained state using input from X-ray diffraction. k Á p theory yields a critical relative aluminum concentration x c ¼ ð0:0960:05Þ for the crossing of the uppermost two valence bands for strain free material, shifting to higher values for compressively strained samples, as supported by polarization dependent PL. The analysis of the strain dependent valence band crossing reconciles the findings of other research groups, where sample strain was neglected. We found a bowing for the energy band gap to the valence band with C 9 symmetry of b C 9 ¼ 0:85eV, and propose a possible bowing for the crystal field energy of b cf ¼ À0:12eV. A comparison of the light extraction efficiency perpendicular and parallel to the c axis of Al x Ga 1Àx N=Al y Ga 1Ày N quantum well structures is discussed for different compositions. V C 2014 AIP Publishing LLC. [http://dx.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Composition dependent valence band order in c-oriented wurtzite AlGaN layers

Neuschl

Helbing

Knab

et al. 2014

Journal of Applied Physics

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“…III‐V nitride semiconductors are widely used in short‐wavelength light‐emitting diodes (LEDs) and laser diodes. AlGaN with a high Al content and AlN are good candidates for deep ultraviolet LEDs and high‐power devices because AlN‐based semiconductors have a wide band gap and high thermal conductivity . To realize these AlN‐based devices, high‐quality and large AlN single‐crystal substrates are required.…”

Section: Introductionmentioning

confidence: 99%

“…AlGaN with a high Al content and AlN are good candidates for deep ultraviolet LEDs and high-power devices because AlN-based semiconductors have a wide band gap and high thermal conductivity. 1,2 To realize these AlN-based devices, high-quality and large AlN single-crystal substrates are required. AlN single-crystal substrates are typically grown using methods such as sublimation, flux growth, and highpressure growth.…”

Section: Introductionmentioning

confidence: 99%

Conditions for growth of AlN single crystals in Al–Sn flux

et al. 2018

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In this study, we investigated the Al–Sn flux system and its growth conditions to obtain AlN single crystals. AlN single crystals of a size of 50 μm were successfully grown using an Al–Sn melt under nitrogen gas pressure. The growable region of the AlN crystals was established using a pressure‐temperature diagram. The required nitrogen gas pressure for the growth of the AlN crystals was found to decrease with increasing temperature, and AlN was grown at 0.1 MPa nitrogen pressure above 1300°C. By investigating the AlN yield with various Al concentrations, we confirmed that the Al component in the Al–Sn melt facilitated nitrogen dissolution. Finally, scanning electron microscopy analysis showed that the obtained AlN particles showed good morphology.

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“…The shortest wavelength achieved with pure AlN LEDs is 210 nm [8]. External quantum efficiency (EQE) of UV LEDs is continuously improving as both internal quantum efficiency (IQE) and light extraction efficiency (LEE) are boosted by various techniques like: migration-enhanced metalorganic chemical vapor deposition [9, 10], ammonia pulsed-flow method [11, 12] and nanowires [13], or surface plasmons [14] and aluminum reflective electrodes [15], respectively. EQE above 10% has been reported when approaches for improving IQE and LEE are applied in combination [16].…”

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confidence: 99%

Light assisted antibiotics

Argyraki

Markvart

Stavnsbjerg

et al. 2017

Preprint

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The overuse of antibiotics is accelerating the bacterial resistance, and therefore there is a need to reduce the amount of antibiotics used for treatment. Here, we demonstrate that specific wavelengths in a narrow range around 296 nm are able to eradicate bacteria in the biofilm state more effectively, than antibiotics and the combination of irradiation and antibiotics is even better, introducing a novel concept light assisted antibiotics. The investigated wavelength range was 249 nm to 338 nm with an approximate step of 5 nm. The novel concept can significantly reduce the amount of antibiotics needed for eradicating mature bacterial biofilms. The irradiation treatment was combined with tobramycin and its efficiency was compared to combinatory antibiotic treatment and highly concentrated antibiotic monotherapy. The eradication efficacies, on mature biofilms, achieved by light assisted antibiotic and by the antibiotic monotherapy at 10-fold higher concentration, were equivalent. The present achievement could motivate the development of light assisted antibiotic treatments for treating infections.There is a worldwide increasing awareness and concern about the 1 antibiotic resistance, which in the future could prevent effective

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Improvement of Light Extraction Efficiency for AlGaN-Based Deep Ultraviolet Light-Emitting Diodes

Cited by 50 publications

References 11 publications

Composition dependent valence band order in c-oriented wurtzite AlGaN layers

Composition dependent valence band order in c-oriented wurtzite AlGaN layers

Conditions for growth of AlN single crystals in Al–Sn flux

Light assisted antibiotics

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