Aluminium incorporation in polar, semi- and non-polar AlGaN layers: a comparative study of x-ray diffraction and optical properties

Dinh, Duc V.; Hu, Nan; Honda, Yoshio; Amano, Hiroshi; Pristovsek, Markus

doi:10.1038/s41598-019-52067-y

Cited by 14 publications

(14 citation statements)

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“…The highest aluminum content is observed for the polar c-plane, while the lowest aluminum incorporation is observed for the nonpolar a-plane. Although this is consistent with reports on planar AlGaN layers grown by MOVPE, 55,56 the variation may be further enhanced by effects related to gasphase transport of precursors in a complex environment of 3D microstructures. The lower emission intensity of the c-plane quantum well with respect to the semipolar and nonpolar QWs may be attributed to the inferior material quality and strongly reduced wavefunction overlap in the polar QW due to the QCSE.…”

Section: ■ Results and Discussionsupporting

confidence: 92%

AlGaN Microfins as Nonpolar UV Emitters Probed by Time-Resolved Cathodoluminescence

2022

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Despite the continuous technological progress and recent commercialization of UV light emitting diodes for sterilization and disinfection applications, the performance of solid-state UV emitters still lags far behind that of their InGaNbased counterparts, which emit in the visible blue−green spectrum. Both fundamental physical aspects and material quality restrictions have been discussed as origin of this striking difference. In this study, GaN/AlGaN core−shell microfins with a-plane sidewalls are proposed as a model system to demonstrate the efficiency potential of ultra-low-defect nonpolar UV emitters. Such structures are manufactured by bottom-up selective-area metalorganic vapor phase epitaxy of GaN microfin cores and further overgrowth of the AlGaN active region, employing a compositionally graded GaN/AlGaN short-period superlattice for strain management. Using this approach, mostly crack-free AlGaN quantum wells emitting around 321 nm could be realized with a threading dislocation density of as low as (6 ± 3) × 10 7 cm −2 . The carrier dynamics within the nonpolar AlGaN structures are studied by time-resolved cathodoluminescence spectroscopy, revealing fast radiative recombination lifetimes down to 0.6 ns and distinct signatures of carrier localization at low temperatures. Delayed carrier emission from localized states within the cladding is proposed to be a cause for anomalously high effective carrier lifetimes observed at temperatures below 80 K. By analyzing the characteristic temperature dependence of radiative and nonradiative recombination processes and fitting the lifetime data with an appropriate model across the whole temperature range, a room-temperature internal quantum efficiency of (40 ± 6) % is estimated for the studied sample. The findings corroborate the interest in nonpolar AlGaN structures as highly efficient UV emitters.

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Section: ■ Results and Discussionsupporting

confidence: 92%

AlGaN Microfins as Nonpolar UV Emitters Probed by Time-Resolved Cathodoluminescence

2022

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“…Growth on semipolar and nonpolar planes results in a reduction of built-in fields [11], which can increase the radiative recombination efficiency of QWs, as already confirmed for InGaN-based LEDs [4,12]. However, similar to semipolar [13][14][15][16][17][18][19] and nonpolar AlGaN [18,[20][21][22], a few studies have been performed for semipolar (112̅ 2) InAlN grown on UV-transparent (112̅ 2) AlN/sapphire templates [23,24]. One of the reasons is the limit of available non-cplane AlN substrates [13,17,21] and templates [25,26].…”

Section: Introductionmentioning

confidence: 89%

Indium incorporation and optical properties of polar, semipolar and nonpolar InAlN

Dinh

Honda

et al. 2020

Semicond. Sci. Technol.

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Indium incorporation and the optical properties of In x Al 1−x N layers (0x0.45) grown by metalorganic vapour phase epitaxy have been investigated simultaneously on polar (0001), untwinned semipolar (101̅ 3) and nonpolar (101̅ 0) AlN templates, which were prepared on planar sapphire substrates. The InN mole fraction (x InN ) of the layers was tuned by changing growth temperature from 660°C to 860°C. x InN determined by x-ray diffraction was found to be comparable for the polar, semipolar and nonpolar surface orientations. This is consistent with comparable effective bandgap energy of the layers obtained from optical transmission measurements at room temperature. The bandgap bowing parameter was found to be strongly composition-dependent. Roomtemperature photoluminescence measurements showed impurity transitions for the layers with x InN 0.2, while InAlN near-band-edge luminescence was observed for the layers with higher x InN .

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“…Comparing the measured AlN alloy fraction for the samples within the same series but of different crystal orientations, one can see that AlN alloy fraction is lower in the semipolar samples, in agreement with [40], although there are reports of different relationships between AlN alloy fraction and orientation [41,47]. For the samples with high V/III ratios, the AlN alloy fraction values are also lower due to increased TMAl:NH 3 pre-reactions and the suppression of GaN decomposition at increased ammonia fluxes [26,48].…”

Section: Wdx Measurementmentioning

confidence: 66%

A systematic comparison of polar and semipolar Si-doped AlGaN alloys with high AlN content

Spasevski

Kusch

Pampili

et al. 2020

J. Phys. D: Appl. Phys.

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With a view to supporting the development of ultra-violet light-emitting diodes and related devices, the compositional, emission and morphology properties of Si-doped n-type Al x Ga1-x N alloys are extensively compared. This study has been designed to determine how the different Al x Ga1-x N crystal orientations (polar (0001) and semipolar (11–22)) affect group-III composition and Si incorporation. Wavelength dispersive x-ray (WDX) spectroscopy was used to determine the AlN mole fraction (x ≈ 0.57–0.85) and dopant concentration (3 × 1018–1 × 1019 cm−3) in various series of Al x Ga1-x N layers grown on (0001) and (11–22) AlN/sapphire templates by metalorganic chemical vapor deposition. The polar samples exhibit hexagonal surface features with Ga-rich boundaries confirmed by WDX mapping. Surface morphology was examined by atomic force microscopy for samples grown with different disilane flow rates and the semipolar samples were shown to have smoother surfaces than their polar counterparts, with an approximate 15% reduction in roughness. Optical characterization using cathodoluminescence (CL) spectroscopy allowed analysis of near-band edge emission in the range 4.0–5.4 eV as well as various deep impurity transition peaks in the range 2.7–4.8 eV. The combination of spatially-resolved characterization techniques, including CL and WDX, has provided detailed information on how the crystal growth direction affects the alloy and dopant concentrations.

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Aluminium incorporation in polar, semi- and non-polar AlGaN layers: a comparative study of x-ray diffraction and optical properties

Cited by 14 publications

References 50 publications

AlGaN Microfins as Nonpolar UV Emitters Probed by Time-Resolved Cathodoluminescence

AlGaN Microfins as Nonpolar UV Emitters Probed by Time-Resolved Cathodoluminescence

Indium incorporation and optical properties of polar, semipolar and nonpolar InAlN

A systematic comparison of polar and semipolar Si-doped AlGaN alloys with high AlN content

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