Epitaxial growth of AlN films on sapphire via a multilayer structure adopting a low- and high-temperature alternation technique

Zhang, X.; Xu, Fujun; Wang, J. M.; He, Chao; Zhang, L. S.; Huang, Jing; Cheng, Jianpeng; Qin, Zhixin; Yang, Xuelin; Tang, Ning; Wang, X. Q.; Shen, Bo

doi:10.1039/c5ce01159k

Cited by 54 publications

(38 citation statements)

References 18 publications

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“…The corresponding screw- and edge- TDDs are estimated to be 6.3 × 10 7 cm −2 and 3.2 × 10 8 cm −2 , respectively13. The crystalline quality of the AlN films is significantly improved in comparison to our previous work14. In addition, our subsequent experiments prove that AlN films with low TDD can be stably and repeatedly acquired from our 15 growth runs using the same epitaxial conditions on the optimized 650/1000 NPSS, with FWHM deviation no more than 5%, which means that a reproducible process for quality control has been achieved for high-quality AlN heteroepitaxy.…”

Section: Resultsmentioning

confidence: 63%

High-quality AlN epitaxy on nano-patterned sapphire substrates prepared by nano-imprint lithography

Zhang

Wang

et al. 2016

Sci Rep

119

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We report epitaxial growth of AlN films with atomically flat surface on nano-patterned sapphire substrates (NPSS) prepared by nano-imprint lithography. The crystalline quality can be greatly improved by using the optimized 1-μm-period NPSS. The X-ray diffraction ω-scan full width at half maximum values for (0002) and (102) reflections are 171 and 205 arcsec, respectively. The optimized NPSS contribute to eliminating almost entirely the threading dislocations (TDs) originating from the AlN/sapphire interface via bending the dislocations by image force from the void sidewalls before coalescence. In addition, reducing the misorientations of the adjacent regions during coalescence adopting the low lateral growth rate is also essential for decreasing TDs in the upper AlN epilayer.

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Section: Resultsmentioning

confidence: 63%

High-quality AlN epitaxy on nano-patterned sapphire substrates prepared by nano-imprint lithography

Zhang

Wang

et al. 2016

Sci Rep

119

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“…These findings also demonstrate that a pure SL growth condition favours film cracking before obtaining a smooth step-flowed surface. According to literature, the 3D mode IL should also lead to a limitation of tensile strain as shown for multilayer deposition with 3D-2D sequences [6,7]. Employing a similar technique in this study, the sample with a pitted IL (Fig.…”

Section: Two-layer Overgrowth Process On Step-bunched Templatesmentioning

confidence: 79%

“…Among various approaches for high-quality AlN grown on sapphire substrates, e.g. multilayer growth [2,6,7] or high-temperature annealing of AlN films [8,9], the deposition by hydride vapour phase epitaxy (HVPE) [10,11] and the growth on nano-patterned sapphire substrates (nano-PSS) by metalorganic vapour phase epitaxy (MOVPE) [12][13][14][15] have been shown to be promising. However, the AlN surface morphology caused by the last two techniques is often defined by macrosteps [11,[13][14][15].…”

Section: Introductionmentioning

confidence: 99%

Reduction of surface roughness by modification of step-bunched aluminum nitride layers towards step-flow morphology

Tillner¹,

Brandl²,

Hoffmann³

et al. 2020

physics

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Conventional aluminum nitride (AlN) template fabrication techniques, like hydride vapour phase epitaxy or AlN growth on patterned sapphire substrates, usually lead to step-bunched template surfaces. The resulting macrosteps cause emission broadening or even multiple-peak characteristics of ultraviolet light-emitting diodes (UV LEDs) fabricated on such AlN templates. In order to reduce these macrosteps and to provide a smoother surface, even without the need of a thick AlN deposition, a two-layer growth procedure is reported here. A three-dimensional (3D) – twodimensional (2D) sequential growth initiates a significant modification of the previous AlN surface morphology and simultaneously limits the evolving tensile strain. A primarily step-bunched surface with a surface roughness root mean square of 1.8 nm is successfully reduced by the two-layer growth procedure down to 0.8 nm, without any film cracking. This distinct roughness reduction of more than 50% is achieved within an AlN thickness of only 1.3 µm. With a smoother surface, the electroluminescence characteristic of a UV LED structure is substantially improved. Instead of a double-peak emission, typical for LEDs grown on step-bunched templates, a single-peak emission and lower spectral width were achieved, indicating the high potential of the suggested two-layer technique for improving performance.

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“…Here one has to take into account the lower lattice constants and the lower TDD of the HTA‐AlN (in comparison to MOVPE‐grown AlN). A possible way to reduce the strong compressive strain in the nonpseudomorphic AlGaN would be the change of the growth mode to a 3D mode as it was shown for the development of low TDD AlN templates with increased AlN layer thickness [ 20,31–34 ] and for UVB‐LED structures [ 10,35 ] as well as recently for the deposition of Al 0.55 Ga 0.45 N layers for UVB laser structures. [ 9 ] However, here the surface needs to be smoothened before the MQW is grown, which again is a challenge.…”

Section: Resultsmentioning

confidence: 99%

The Impact of AlN Templates on Strain Relaxation Mechanisms during the MOVPE Growth of UVB‐LED Structures

Knauer

Mogilatenko

Weinrich

et al. 2020

Crystal Research and Technology

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Strain relaxation mechanisms in AlGaN based light emitting diodes emitting in the ultraviolet B spectral range (UVB‐LEDs) grown on different AlN/sapphire templates are analyzed by combining in situ reflectivity and curvature data with transmission electron microscopy. In particular, the impact of dislocation density, surface morphology, and lattice constant of the AlN/sapphire templates is studied. For nonannealed AlN/templates with threading dislocation densities (TDDs) of 4 × 109 and 3 × 109 cm−2 and different surface morphologies strain relaxation takes place mostly by conventional ways, such as inclination of threading dislocation lines and formation of horizontal dislocation bands. In contrast, a TDD reduction down to 1 × 109 cm−2 as well as a reduction of the lattice constant of high temperature annealed AlN template leads to drastic changes in the structure of subsequently grown AlGaN layers, e.g., to transformation to helical dislocations and enhanced surface enlargement by formation of macrofacets. For the growth of strongly compressively strained AlGaN layers for UVB‐LEDs the relaxation mechanism is strongly influenced by the absolute values of TDD and the lattice constant of the AlN templates and is less influenced by their surface morphology.

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Epitaxial growth of AlN films on sapphire via a multilayer structure adopting a low- and high-temperature alternation technique

Cited by 54 publications

References 18 publications

High-quality AlN epitaxy on nano-patterned sapphire substrates prepared by nano-imprint lithography

High-quality AlN epitaxy on nano-patterned sapphire substrates prepared by nano-imprint lithography

Reduction of surface roughness by modification of step-bunched aluminum nitride layers towards step-flow morphology

The Impact of AlN Templates on Strain Relaxation Mechanisms during the MOVPE Growth of UVB‐LED Structures

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