# The In-Plane-Two-Folders Symmetric a-Plane AlN Epitaxy on r-Plane Sapphire Substrate

^{1}

^{2}

^{3}

^{4}

^{5}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Experiment

#### 2.1. Synthesis

#### 2.2. X-ray Diffraction (XRD) Characterization

_{α1}X-ray, with λ = 0.154056 nm.

#### 2.3. Atomic Force Microscopy (AFM) Characterization

#### 2.4. Raman Spectroscopy Characterization

## 3. Result and Discussion

^{−1}. For AlN film, three vibration peaks were seen: the A

_{1}(TO), E

_{2}

^{H}, and E

_{1}(TO) modes at around 644.2, 663.2, and 675.8 cm

^{−1}; the corresponding vibration mode schemes are shown in Figure 3b. The appearance of all Raman signals indicates the good crystallinity of the annealed samples.

_{1}(TO) mode did not change very much, despite it being under the annealing operation, including both the FWHM and Raman shift. In addition, it can be observed that the A

_{1}(TO) vibration presents a redshift feature upon increasing thickness. A similar characteristic was observed in a-AlN with buffers grown at different temperatures, which resulted from the introduced strain [30,31]. However, the HTA had an obvious contribution to the E

_{2}

^{H}peak, and it can be noted that both the FWHM and Raman wavenumber were greatly decreased by HTA. The FWHM reduction mainly resulted from the improvement of crystalline quality; however, the decreased Raman wavenumber was caused by the strain resetting after annealing. When compared with the strain-free E

_{2}

^{H}signal at 657 cm

^{−1}in bulk AlN, our as-grown a-AlNs present a blueshift, while the annealed samples exhibit a redshift. According to previous studies [32], the phonon frequency reduction and increase are caused by the lattice expansion and shrinkage, respectively. The Raman results are in agreement with the XRD 2Theta-Omega scans.

## 4. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

- Nanishi, Y. The birth of the blue LED. Nat. Photonics
**2014**, 8, 884–886. [Google Scholar] [CrossRef] - Amano, H.; Kito, M.; Hiramatsu, K.; Akasaki, I. P-Type Conduction in Mg-Doped GaN Treated with Low-Energy Electron Beam Irradiation (LEEBI). Jpn. J. Appl. Phys.
**1989**, 28, L2112. [Google Scholar] [CrossRef] - Nakamura, S.; Senoh, M.; Nagahama, S.-I.; Iwasa, N.; Yamada, T.; Matsushita, T.; Kiyoku, H.; Sugimoto, Y. InGaN-Based Multi-Quantum-Well-Structure Laser Diodes. Jpn. J. Appl. Phys.
**1996**, 35, L74. [Google Scholar] [CrossRef] - Nakamura, S.; Mukai, T.; Senoh, M. High-Power GaN P-N Junction Blue-Light-Emitting Diodes. Jpn. J. Appl. Phys.
**1991**, 30, L1998. [Google Scholar] [CrossRef] - Nakamura, S.; Senoh, M.; Iwasa, N.; Nagahama, S.-i. High-Brightness InGaN Blue, Green and Yellow Light-Emitting Diodes with Quantum Well Structures. Jpn. J. Appl. Phys.
**1995**, 34, L797. [Google Scholar] [CrossRef] - Takeuchi, T.; Sota, S.; Katsuragawa, M.; Komori, M.; Takeuchi, H.; Amano, H.; Akasaki, I. Quantum-Confined Stark Effect due to Piezoelectric Fields in GaInN Strained Quantum Wells. Jpn. J. Appl. Phys.
**1997**, 36, L382. [Google Scholar] [CrossRef] - Leroux, M.; Grandjean, N.; Laügt, M.; Massies, J.; Gil, B.; Lefebvre, P.; Bigenwald, P. Quantum confined Stark effect due to built-in internal polarization fields in (Al,Ga)N/GaN quantum wells. Phys. Rev. B
**1998**, 58, R13371(R). [Google Scholar] [CrossRef] - Masui, H.; Sonoda, J.; Pfaff, N.; Koslow, I.; Nakamura, S.; DenBaars, S.P. Quantum-confined Stark effect on photoluminescence and electroluminescence characteristics of InGaN-based light-emitting diodes. J. Phys. D Appl. Phys.
**2008**, 41, 165105. [Google Scholar] [CrossRef] - Guo, Q.; Kirste, R.; Mita, S.; Tweedie, J.; Reddy, P.; Washiyama, S.; Breckenridge, M.H.; Collazo, R.; Sitar, Z. The polarization field in Al-rich AlGaN multiple quantum wells. Jpn. J. Appl. Phys.
**2019**, 58, SCCC10. [Google Scholar] [CrossRef] - Schlichting, S.; Hönig, G.M.O.; Müßener, J.; Hille, P.; Grieb, T.; Westerkamp, S.; Teubert, J.; Schörmann, J.; Wagner, M.R.; Rosenauer, A.; et al. Suppression of the quantum-confined Stark effect in polar nitride heterostructures. Commun. Phys.
**2018**, 1, 48. [Google Scholar] [CrossRef] [Green Version] - Kneissl, M.; Seong, T.-Y.; Han, J.; Amano, H. The emergence and prospects of deep-ultraviolet light-emitting diode technologies. Nat. Photonics
**2019**, 13, 233–244. [Google Scholar] [CrossRef] - Reich, C.; Guttmann, M.; Feneberg, M.; Wernicke, T.; Mehnke, F.; Kuhn, C.; Rass, J.; Lapeyrade, M.; Einfeldt, S.; Knauer, A.; et al. Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes. Appl. Phys. Lett.
**2015**, 107, 142101. [Google Scholar] [CrossRef] - Li, Y.; Wang, C.; Zhang, Y.; Hu, P.; Zhang, S.; Du, M.; Su, X.; Li, Q.; Yun, F. Analysis of TM/TE mode enhancement and droop reduction by a nanoporous n-AlGaN underlayer in a 290 nm UV-LED. Photonics Res.
**2020**, 8, 806–811. [Google Scholar] [CrossRef] - Kashima, Y.; Maeda, N.; Matsuura, E.; Jo, M.; Iwai, T.; Morita, T.; Kokubo, M.; Tashiro, T.; Kamimura, R.; Osada, Y. High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer. Appl. Phys. Express
**2018**, 11, 012101. [Google Scholar] [CrossRef] - Feezell, D.F.; Speck, J.S.; DenBaars, S.P.; Nakamura, S. Semipolar $\left(20\overline{2}\overline{1}\right)$ InGaN/GaN Light-Emitting Diodes for High-Efficiency Solid-State Lighting. J. Disp. Technol.
**2013**, 9, 190–198. [Google Scholar] [CrossRef] - Zhao, Y.; Sonoda, J.; Pan, C.-C.; Brinkley, S.; Koslow, I.; Fujito, K.; Ohta, H.; DenBaars, S.P.; Nakamura, S. 30-mW-Class High-Power and High-Efficiency Blue Semipolar (1011) InGaN/GaN Light-Emitting Diodes Obtained by Backside Roughening Technique. Appl. Phys. Express
**2010**, 3, 102101. [Google Scholar] [CrossRef] [Green Version] - Sato, H.; Tyagi, A.; Zhong, H.; Fellows, N.; Chung, R.B.; Saito, M.; Fujito, K.; Speck, J.S.; DenBaars, S.P.; Nakamura, S. High power and high efficiency green light emitting diode on free-standing semipolar $\left(112\overline{2}\right)$ bulk GaN substrate. Phys. Stat. Sol. (RRL)
**2007**, 1, 162–164. [Google Scholar] [CrossRef] - Jinno, D.; Otsuki, S.; Niimi, T.; Sugimori, S.; Daicho, H.; Iwaya, M.; Takeuchi, T.; Kamiyama, S.; Akasaki, I. Annealing of the sputtered AlN buffer layer on r-plane sapphire and its effect on a-plane GaN crystalline quality. Phys. Stat. Sol (b)
**2017**, 254, 1600723. [Google Scholar] [CrossRef] - Dinh, D.V.; Hu, N.; Honda, Y.; Amano, H.; Pristovsek, M. High-temperature thermal annealing of nonpolar (100) AlN layers sputtered on (100) sapphire. J. Cryst Growth
**2018**, 498, 377–380. [Google Scholar] [CrossRef] - Jo, M.; Hirayam, H. Growth of non-polar a-plane AlN on r-plane sapphire. Jpn. J. Appl. Phys.
**2016**, 55, 05FA02. [Google Scholar] [CrossRef] - Lin, C.-H.; Yamashita, Y.; Miyake, H.; Hiramatsu, K. Fabrication of high-crystallinity a-plane AlN films grown on r-plane sapphire substrates by modulating buffer-layer growth temperature and thermal annealing conditions. J. Cryst Growth
**2017**, 468, 845–850. [Google Scholar] - Hayashi, Y.; Uesugi, K.; Shojiki, K.; Tohei, T.; Sakai, A.; Miyake, H. Thermal strain analysis considering in-plane anisotropy for sputtered AlN on c- and a-plane sapphire under high-temperature annealing. AIP Adv.
**2021**, 11, 095012. [Google Scholar] [CrossRef] - Yin, J.; Zhou, B.; Li, L.; Liu, Y.; Guo, W.; Talwar, D.N.; He, K.; Ferguson, I.T.; Wan, L.; Feng, Z.C. Optical and structural properties of AlN thin films deposited on different faces of sapphire substrates. Semicond. Sci. Technol.
**2021**, 36, 045012. [Google Scholar] [CrossRef] - Peng, X.; Sun, J.; Liu, H.; Li, L.; Wang, Q.; Wu, L.; Guo, W.; Meng, F.; Chen, L.; Huang, F.; et al. Structural and optical properties of AlN sputtering deposited on sapphire substrates with various orientations. J. Semicond.
**2022**, 43, 022801. [Google Scholar] [CrossRef] - Miyake, H.; Lin, C.-H.; Tokoro, K.; Hiramatsu, K. Preparation of high-quality AlN on sapphire by high-temperature face-to-face annealing. J. Cryst Growth
**2016**, 456, 155–159. [Google Scholar] [CrossRef] [Green Version] - Susilo, N.; Hagedorn, S.; Jaeger, D.; Miyake, H.; Zeimer, U.; Reich, C.; Neuschulz, B.; Sulmoni, L.; Guttmann, M.; Mehnke, F.; et al. AlGaN-based deep UV LEDs grown on sputtered and high temperature annealed AlN/sapphire. Appl. Phys. Lett.
**2018**, 112, 041110. [Google Scholar] [CrossRef] - Wang, D.; Uesugi, K.; Xiao, S.; Norimatsu, K.; Miyake, H. Low dislocation density AlN on sapphire prepared by double sputtering and annealing. Appl. Phys. Express
**2020**, 13, 095501. [Google Scholar] [CrossRef] - Miyagawa, R.; Miyake, H.; Hiramatsu, K. a-plane AlN and AlGaN growth on r-plane sapphire by MOVPE. Phys. Stat. Sol (c)
**2010**, 7, 2107–2110. [Google Scholar] [CrossRef] - Tahtamouni, T.A.; Sedhain, A.; Lin, J.Y.; Jiang, H.X. Growth and optical properties of a-plane AlN and Al rich AlN/AlxGa1–xN quantum wells grown on r-plane sapphire substrates. Phys. Stat. Sol. (c)
**2008**, 5, 1568–1570. [Google Scholar] [CrossRef] - Dai, Y.; Wang, W.; Gui, C.; Wen, X.; Peng, Q.; Liu, S. A first-principles study of the mechanical properties of AlN with Raman verification. Comput. Mater. Sci.
**2016**, 112, 342–346. [Google Scholar] [CrossRef] - Chen, S.; Zhang, X.; Wang, S.; Fan, A.; He, J.; Li, C.; Lu, L.; Rao, L.; Zhuang, Z.; Hu, G.; et al. High quality non-polar a-plane AlN template grown on semi-polar r-plane sapphire substrate by three-step pulsed flow growth method. J. Alloys Compd.
**2021**, 872, 159706. [Google Scholar] [CrossRef] - Kuballa, M.; Hayes, J.M.; Shi, Y.; Edgar, J.H.; Prins, A.D.; van Uden, N.W.A.; Dunstan, D.J. Raman scattering studies on single-crystalline bulk AlN: Temperature and pressure dependence of the AlN phonon modes. J. Cryst Growth
**2001**, 231, 391–396. [Google Scholar] [CrossRef] - Shibata, T.; Asai, K.; Nakamura, Y.; Tanaka, M.; Kaigawa, K.; Shibata, J.; Sakai, H. AlN epitaxial growth on off-angle R-plane sapphire substrates by MOCVD. J. Cryst Growth
**2001**, 229, 63–68. [Google Scholar] [CrossRef] - Wu, J.-J.; Okuura, K.; Fujita, K.; Okumura, K.; Miyake, H.; Hiramatsu, K. Influence of off-cut angle of r-plane sapphire on the crystal quality of nonpolar a-plane AlN by LP-HVPE. J. Cryst Growth
**2009**, 311, 4473–4477. [Google Scholar] [CrossRef] - Adachi, M.; Fukuyama, H. Non-Polar a-Plane AlN Growth on Nitrided r-Plane Sapphire by Ga–Al Liquid-Phase Epitaxy. Phys. Stat. Sol (a)
**2018**, 255, 1700478. [Google Scholar] [CrossRef] - Okada, N.; Katoa, N.; Satoa, S.; Sumiia, T.; Fujimotoa, N.; Imuraa, M.; Balakrishnana, K.; Iwayaa, M.; Kamiyamaa, S.; Amanoa, H.; et al. Epitaxial lateral overgrowth of a-AlN layer on patterned a-AlN template by HT-MOVPE. J. Cryst Growth
**2007**, 300, 141–144. [Google Scholar] [CrossRef]

**Figure 1.**XRD rocking curves of (

**a**) (110) and (

**b**) (100) planes of as-grown and annealed 500 nm thick samples; (

**c**) thickness-dependent FWHMs of (110) and (100) plane rocking curves of annealed AlN samples.

**Figure 2.**XRD 2Theta-Omega scans of as-grown and annealed samples, when the scanning directions are along the AlN (

**a**) out-of-plane $\left[11\overline{2}0\right]$ and (

**b**) specific $\left[1\overline{1}00\right]$ directions; (

**c**) the 2Theta-Omega scans along the $\left[11\overline{2}0\right]$ direction of annealed AlN samples with different thicknesses.

**Figure 3.**(

**a**) The full Raman spectra of annealed samples with different thicknesses, and the phonon vibration signals of the sapphire substrate and AlN epilayer are labelled; (

**b**) the scheme of different phonon vibration modes in the AlN lattice.

**Figure 4.**The region of Raman spectra from 630 to 680 cm

^{−1}of (

**a**) as-grown and (

**b**) annealed samples; the FWHM (blue open labels) and Raman shift (red solid labels) of (

**c**) A

_{1}(TO) and (

**d**) E

_{2}

^{H}modes, as dependent on the thickness of the as-grown (diamonds) and annealed (squares) samples.

**Figure 5.**(

**a**) The XRD phi-dependent polar figures of r-sapphire substrate (006) and a-AlN (100) film, it is clearly observed that the in-plane components of the AlN and sapphire are both vertical. (

**b**) The lattice scheme of the a-AlN and r-sapphire from the out-of-plane direction (r-direction of sapphire and a-direction of AlN); (

**c**) three-dimensional crystalline scheme of the epitaxial relationship between the sapphire substrate and AlN epilayer.

**Figure 6.**(

**a**) Chi scans of the (100) plane of AlN samples with 500 and 1000 nm thickness after calibrating the $\left[11\overline{2}0\right]$ direction of the sapphire substrates; (

**b**) the corresponding scheme of lattice distortion describe in (

**a**).

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. |

© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Zhang, F.; Huang, L.; Zhang, J.; Liang, Z.; Zhang, C.; Liu, S.; Luo, W.; Kang, J.; Cao, J.; Li, T.;
et al. The In-Plane-Two-Folders Symmetric *a*-Plane AlN Epitaxy on *r*-Plane Sapphire Substrate. *Symmetry* **2022**, *14*, 573.
https://doi.org/10.3390/sym14030573

**AMA Style**

Zhang F, Huang L, Zhang J, Liang Z, Zhang C, Liu S, Luo W, Kang J, Cao J, Li T,
et al. The In-Plane-Two-Folders Symmetric *a*-Plane AlN Epitaxy on *r*-Plane Sapphire Substrate. *Symmetry*. 2022; 14(3):573.
https://doi.org/10.3390/sym14030573

**Chicago/Turabian Style**

Zhang, Fabi, Lijie Huang, Jin Zhang, Zhiwen Liang, Chenhui Zhang, Shangfeng Liu, Wei Luo, Junjie Kang, Jiakang Cao, Tai Li,
and et al. 2022. "The In-Plane-Two-Folders Symmetric *a*-Plane AlN Epitaxy on *r*-Plane Sapphire Substrate" *Symmetry* 14, no. 3: 573.
https://doi.org/10.3390/sym14030573