Research on the critical thickness of Al<sub>0.2</sub>Ga<sub>0.8</sub>N template grown on AlN/sapphire substrate

Yaqin Li; Jianping Liu; Aiqin Tian; Masao Ikeda; Wei Zhou; Hui Yang

doi:10.1088/1674-4926/26030007

J. Semicond. > Just Accepted

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Research on the critical thickness of Al_0.2Ga_0.8N template grown on AlN/sapphire substrate

Yaqin Li^{1, 2, 3}, Jianping Liu^{1, 2, 3,}, Aiqin Tian^{2, 3,}, Masao Ikeda^{2, 3}, Wei Zhou^{2, 3} and Hui Yang^{1, 2, 3}

+ Author Affiliations

Corresponding author: Jianping Liu, jpliu2010@sinano.ac.cn; Aiqin Tian, aqtian2012@sinano.ac.cn

DOI: 10.1088/1674-4926/26030007CSTR: 32376.14.1674-4926.26030007

Abstract: AlGaN-based ultraviolet (UV) laser diodes (LDs), with emission wavelength in the 280–365 nm range, are promising for applications in medical diagnostics and biological sensing, making them a prominent research focus in both academia and industry in recent years. A key challenge in their development is the large stress induced during the epitaxial growth of LD structures, which arises from the lack of lattice-matched substrates, and severely degrades the quantum efficiency and overall LD performance. This study presents an in-depth investigation into the growth mode and stress evolution of thick Al_0.2Ga_0.8N template. Firstly, we used the compressive stress between the Al_0.2Ga_0.8N layer and AlN/Sapphire substrate to form spontaneously three-dimensional growth to annihilate dislocations. Secondly, based on the Nakajima's theory of elasticity, we refined the conventional theoretical models for AlGaN strain relaxation of the S-K growth mode and critical thickness by considering the crucial role of threading dislocations (TDs) in releasing compressive stress. The experimentally measured critical thickness for three-dimensional growth was consistent with the calculated results. Furthermore, a crack-free high-quality 5 μm-thick Al_0.2Ga_0.8N template was successfully grown on an AlN/sapphire substrate.

Key words: ultraviolet lasers, strain relaxation, critical thickness

References

[1]	Kneissl M, Rass J. III-Nitride Ultraviolet Emitters: Technology and Applications. Cham: Springer International Publishing, 2016
[2]	Hargis P J Jr, Sobering T J, Tisone G C, et al. Ultraviolet fluorescence identification of protein, DNA, and bacteria. Opt Instrum Gas Emiss Monit Atmos Meas, 1995, 2366: 147 doi: 10.1117/12.205554
[3]	Xie N, Xu F J, Wang J M, et al. Stress evolution in AlN growth on nano-patterned sapphire substrates. Appl Phys Express, 2020, 13(1): 015504 doi: 10.7567/1882-0786/ab582c
[4]	Hagedorn S, Mogilatenko A, Walde S, et al. High-temperature annealing and patterned AlN/sapphire interfaces. Phys Status Solidi B:, 2021, 258(10): 2100187 doi: 10.1002/pssb.202100187
[5]	Uesugi K, Miyake H. Fabrication of AlN templates by high-temperature face-to-face annealing for deep UV LEDs. Jpn J Appl Phys, 2021, 60(12): 120502 doi: 10.35848/1347-4065/ac3026
[6]	Uesugi K, Kuboya S, Shojiki K, et al. 263 nm wavelength UV-C LED on face-to-face annealed sputter-deposited AlN with low screw- and mixed-type dislocation densities. Appl Phys Express, 2022, 15(5): 055501 doi: 10.35848/1882-0786/ac66c2
[7]	Lu S P, Ben J W, Jiang K, et al. 6-inch AlN epitaxial films with low dislocation densities via MOCVD. J Semicond, 2025, 46(2): 022501 doi: 10.1088/1674-4926/24110030
[8]	Amano H, Collazo R, De Santi C, et al. The 2020 UV emitter roadmap. J Phys D: Appl Phys, 2020, 53(50): 503001 doi: 10.1088/1361-6463/aba64c
[9]	Bryan I, Bryan Z, Mita S, et al. The role of surface kinetics on composition and quality of AlGaN. J Cryst Growth, 2016, 451: 65 doi: 10.1016/j.jcrysgro.2016.06.055
[10]	Sato K, Yasue S, Yamada K, et al. Room-temperature operation of AlGaN ultraviolet-B laser diode at 298 nm on lattice-relaxed Al_0.6Ga_0.4N/AlN/sapphire. Appl Phys Express, 2020, 13(3): 031004
[11]	Fischer A, Kühne H, Richter H. New approach in equilibrium theory for strained layer relaxation. Phys Rev Lett, 1994, 73(20): 2712 doi: 10.1103/PhysRevLett.73.2712
[12]	Orr B G, Kessler D, Snyder C W, et al. A model for strain-induced roughening and coherent island growth. Europhys Lett, 1992, 19(1): 33 doi: 10.1209/0295-5075/19/1/006
[13]	Frank F C, van der Merwe J H. One-dimensional dislocations. I. static theory. Proc R Soc Lond Ser A Math Phys Sci, 1949, 198(1053): 205
[14]	Volmer M. Nucleus formation in supersaturated systems. Zeitschrift für Physikalische Chemie, 1926, 119: 277
[15]	Stranski I N, Krastanov L. Theory of orientation separation of ionic crystals. Akad Wiss Let Mainz Math Natur Kl IIb, 1939, 146: 797
[16]	Nakajima K, Ujihara T, Miyashita S, et al. Effects of misfit dislocations and AlN buffer layer on the GaInN/GaN phase diagram of the growth mode. J Appl Phys, 2001, 89(1): 146 doi: 10.1063/1.1330247
[17]	Zhao W, Wang L, Wang J X, et al. Theoretical study on critical thicknesses of InGaN grown on (0001) GaN. J Cryst Growth, 2011, 327(1): 202 doi: 10.1016/j.jcrysgro.2011.05.002
[18]	Harutyunyan V S, Aivazyan A P, Weber E R, et al. High-resolution X-ray diffraction strain-stress analysis of GaN/sapphire heterostructures. J Phys D: Appl Phys, 2001, 34(10A): A35 doi: 10.1088/0022-3727/34/10A/308
[19]	Huang S Y, Yang J R. A transmission electron microscopy observation of dislocations in GaN grown on (0001) sapphire by metal organic chemical vapor deposition. Jpn J Appl Phys, 2008, 47(10R): 7998 doi: 10.1143/JJAP.47.7998
[20]	Nakajima K. Equilibrium phase diagrams for stranski-krastanov structure mode of III–V ternary quantum dots. Jpn J Appl Phys, 1999, 38(4R): 1875 doi: 10.1143/JJAP.38.1875
[21]	Mohamad R, Béré A, Hounkpati V, et al. A theoretical investigation of the miscibility and structural properties of In_xAl_yGa_1−x−yN alloys. Phys Status Solidi B:, 2018, 255(5): 1700394 doi: 10.1002/pssb.201700394
[22]	Vurgaftman I, Meyer J R. Band parameters for nitrogen-containing semiconductors. J Appl Phys, 2003, 94(6): 3675 doi: 10.1063/1.1600519
[23]	Sohi P, Martin D, Grandjean N. Critical thickness of GaN on AlN: Impact of growth temperature and dislocation density. Semicond Sci Technol, 2017, 32(7): 075010 doi: 10.1088/1361-6641/aa7248
[24]	Li Y Q, Tian A Q, Liu J P, et al. Two-step growth of crack-free 5 μm-thick Al_0.2Ga_0.8N on sapphire substrate with sputtered AlN nucleation layer. J Appl Phys, 2025, 137(6): 065703 doi: 10.1063/5.0249836
[25]	Iwaya M, Tanaka S, Omori T, et al. Recent development of UV-B laser diodes. Jpn J Appl Phys, 2022, 61(4): 040501 doi: 10.35848/1347-4065/ac3be8

Fig. 1. (Color online) Measurement results of reflectance intensities by in situ observation of 5 μm Al_0.2Ga_0.8N using Two-step growth method

DownLoad: Full-Size Img PowerPoint

Fig. 2. (Color online) Cross-section TEM images of Al_0.2Ga_0.8N

DownLoad: Full-Size Img PowerPoint

Fig. 3. (Color online) Critical thicknesses of 3D growth versus Al-content of AlGaN with different density of dislocation

DownLoad: Full-Size Img PowerPoint

Fig. 4. (Color online) (a) FWHM values of (0002) and (10-12) measured by X-ray rocking curves for the 5 μm Al_0.2Ga_0.8N using two-step growth method; (b) Relation between AlN molar fraction and dislocation density of AlGaN with a film thickness of over 1 μm

DownLoad: Full-Size Img PowerPoint

Table 1. Parameters used in calculation

Parameter		AlN	GaN
Lateral lattice constant of a (nm)		0.3112	0.3189
Young’s modulus ${Y} $ (GPa)		340	329
Elastic constants C_ij	C₁₁/GPa	396	390
	C₁₂/GPa	137	145
	C₁₃/GPa	108	106
	C₃₃/GPa	373	398

DownLoad: CSV

[1]	Kneissl M, Rass J. III-Nitride Ultraviolet Emitters: Technology and Applications. Cham: Springer International Publishing, 2016
[2]	Hargis P J Jr, Sobering T J, Tisone G C, et al. Ultraviolet fluorescence identification of protein, DNA, and bacteria. Opt Instrum Gas Emiss Monit Atmos Meas, 1995, 2366: 147 doi: 10.1117/12.205554
[3]	Xie N, Xu F J, Wang J M, et al. Stress evolution in AlN growth on nano-patterned sapphire substrates. Appl Phys Express, 2020, 13(1): 015504 doi: 10.7567/1882-0786/ab582c
[4]	Hagedorn S, Mogilatenko A, Walde S, et al. High-temperature annealing and patterned AlN/sapphire interfaces. Phys Status Solidi B:, 2021, 258(10): 2100187 doi: 10.1002/pssb.202100187
[5]	Uesugi K, Miyake H. Fabrication of AlN templates by high-temperature face-to-face annealing for deep UV LEDs. Jpn J Appl Phys, 2021, 60(12): 120502 doi: 10.35848/1347-4065/ac3026
[6]	Uesugi K, Kuboya S, Shojiki K, et al. 263 nm wavelength UV-C LED on face-to-face annealed sputter-deposited AlN with low screw- and mixed-type dislocation densities. Appl Phys Express, 2022, 15(5): 055501 doi: 10.35848/1882-0786/ac66c2
[7]	Lu S P, Ben J W, Jiang K, et al. 6-inch AlN epitaxial films with low dislocation densities via MOCVD. J Semicond, 2025, 46(2): 022501 doi: 10.1088/1674-4926/24110030
[8]	Amano H, Collazo R, De Santi C, et al. The 2020 UV emitter roadmap. J Phys D: Appl Phys, 2020, 53(50): 503001 doi: 10.1088/1361-6463/aba64c
[9]	Bryan I, Bryan Z, Mita S, et al. The role of surface kinetics on composition and quality of AlGaN. J Cryst Growth, 2016, 451: 65 doi: 10.1016/j.jcrysgro.2016.06.055
[10]	Sato K, Yasue S, Yamada K, et al. Room-temperature operation of AlGaN ultraviolet-B laser diode at 298 nm on lattice-relaxed Al_0.6Ga_0.4N/AlN/sapphire. Appl Phys Express, 2020, 13(3): 031004
[11]	Fischer A, Kühne H, Richter H. New approach in equilibrium theory for strained layer relaxation. Phys Rev Lett, 1994, 73(20): 2712 doi: 10.1103/PhysRevLett.73.2712
[12]	Orr B G, Kessler D, Snyder C W, et al. A model for strain-induced roughening and coherent island growth. Europhys Lett, 1992, 19(1): 33 doi: 10.1209/0295-5075/19/1/006
[13]	Frank F C, van der Merwe J H. One-dimensional dislocations. I. static theory. Proc R Soc Lond Ser A Math Phys Sci, 1949, 198(1053): 205
[14]	Volmer M. Nucleus formation in supersaturated systems. Zeitschrift für Physikalische Chemie, 1926, 119: 277
[15]	Stranski I N, Krastanov L. Theory of orientation separation of ionic crystals. Akad Wiss Let Mainz Math Natur Kl IIb, 1939, 146: 797
[16]	Nakajima K, Ujihara T, Miyashita S, et al. Effects of misfit dislocations and AlN buffer layer on the GaInN/GaN phase diagram of the growth mode. J Appl Phys, 2001, 89(1): 146 doi: 10.1063/1.1330247
[17]	Zhao W, Wang L, Wang J X, et al. Theoretical study on critical thicknesses of InGaN grown on (0001) GaN. J Cryst Growth, 2011, 327(1): 202 doi: 10.1016/j.jcrysgro.2011.05.002
[18]	Harutyunyan V S, Aivazyan A P, Weber E R, et al. High-resolution X-ray diffraction strain-stress analysis of GaN/sapphire heterostructures. J Phys D: Appl Phys, 2001, 34(10A): A35 doi: 10.1088/0022-3727/34/10A/308
[19]	Huang S Y, Yang J R. A transmission electron microscopy observation of dislocations in GaN grown on (0001) sapphire by metal organic chemical vapor deposition. Jpn J Appl Phys, 2008, 47(10R): 7998 doi: 10.1143/JJAP.47.7998
[20]	Nakajima K. Equilibrium phase diagrams for stranski-krastanov structure mode of III–V ternary quantum dots. Jpn J Appl Phys, 1999, 38(4R): 1875 doi: 10.1143/JJAP.38.1875
[21]	Mohamad R, Béré A, Hounkpati V, et al. A theoretical investigation of the miscibility and structural properties of In_xAl_yGa_1−x−yN alloys. Phys Status Solidi B:, 2018, 255(5): 1700394 doi: 10.1002/pssb.201700394
[22]	Vurgaftman I, Meyer J R. Band parameters for nitrogen-containing semiconductors. J Appl Phys, 2003, 94(6): 3675 doi: 10.1063/1.1600519
[23]	Sohi P, Martin D, Grandjean N. Critical thickness of GaN on AlN: Impact of growth temperature and dislocation density. Semicond Sci Technol, 2017, 32(7): 075010 doi: 10.1088/1361-6641/aa7248
[24]	Li Y Q, Tian A Q, Liu J P, et al. Two-step growth of crack-free 5 μm-thick Al_0.2Ga_0.8N on sapphire substrate with sputtered AlN nucleation layer. J Appl Phys, 2025, 137(6): 065703 doi: 10.1063/5.0249836
[25]	Iwaya M, Tanaka S, Omori T, et al. Recent development of UV-B laser diodes. Jpn J Appl Phys, 2022, 61(4): 040501 doi: 10.35848/1347-4065/ac3be8

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Received: 27 April 2026 Revised: 03 May 2026 Online: Accepted Manuscript: 03 June 2026

Article Navigation > Journal of Semiconductors > 2026 > Accepted Manuscript

Yaqin Li, Jianping Liu, Aiqin Tian, Masao Ikeda, Wei Zhou, Hui Yang. Research on the critical thickness of Al0.2Ga0.8N template grown on AlN/sapphire substrate[J]. Journal of Semiconductors, 2026, In Press. doi: 10.1088/1674-4926/26030007 ****Y Q Li, J P Liu, A Q Tian, M Ikeda, W Zhou, and H Yang, Research on the critical thickness of Al0.2Ga0.8N template grown on AlN/sapphire substrate[J]. J. Semicond., 2026, accepted doi: 10.1088/1674-4926/26030007

Citation:

Yaqin Li, Jianping Liu, Aiqin Tian, Masao Ikeda, Wei Zhou, Hui Yang. Research on the critical thickness of Al_0.2Ga_0.8N template grown on AlN/sapphire substrate[J]. Journal of Semiconductors, 2026, In Press. doi: 10.1088/1674-4926/26030007 ****

Y Q Li, J P Liu, A Q Tian, M Ikeda, W Zhou, and H Yang, Research on the critical thickness of Al_0.2Ga_0.8N template grown on AlN/sapphire substrate[J]. J. Semicond., 2026, accepted doi: 10.1088/1674-4926/26030007

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Research on the critical thickness of Al_0.2Ga_0.8N template grown on AlN/sapphire substrate

DOI: 10.1088/1674-4926/26030007

CSTR: 32376.14.1674-4926.26030007

Yaqin Li^{1, 2, 3},
Jianping Liu^{1, 2, 3,},
Aiqin Tian^{2, 3,},
Masao Ikeda^{2, 3},
Wei Zhou^{2, 3},
Hui Yang^{1, 2, 3}

1.
School of Nano-Tech and Nano-Bionics, University of Science and Technology of China, Hefei 230026, China
2.
Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China
3.
Key Laboratory of Semiconductor Display Materials and Chips, Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China

More Information

Yaqin Li got her bachelor’s degree in 2016 from Hebei University of Technology. Now she is a doctoral student at University of Science and Technology of China under the supervision of Prof. Jianping Liu. Her research focuses on MOCVD growth and GaN-Based Laser Diodes
Jianping Liu got his doctoral degree in 2004 from Institute of Semiconductors, Chinese Academy of Sciences. He is currently a Professor with the Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences. His current research interests include GaN-based materials and devices, and MOCVD technology
Aiqin Tian got her doctoral degree in 2017 from University of Chinese Academy of Sciences. She is currently a Professor with the Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences. Her research focuses on GaN-based optoelectronic materials and devices
Corresponding author: jpliu2010@sinano.ac.cn; aqtian2012@sinano.ac.cn
Received Date: 2026-04-27
Revised Date: 2026-05-03

Available Online: 2026-06-03

Abstract

Abstract

AlGaN-based ultraviolet (UV) laser diodes (LDs), with emission wavelength in the 280–365 nm range, are promising for applications in medical diagnostics and biological sensing, making them a prominent research focus in both academia and industry in recent years. A key challenge in their development is the large stress induced during the epitaxial growth of LD structures, which arises from the lack of lattice-matched substrates, and severely degrades the quantum efficiency and overall LD performance. This study presents an in-depth investigation into the growth mode and stress evolution of thick Al_0.2Ga_0.8N template. Firstly, we used the compressive stress between the Al_0.2Ga_0.8N layer and AlN/Sapphire substrate to form spontaneously three-dimensional growth to annihilate dislocations. Secondly, based on the Nakajima's theory of elasticity, we refined the conventional theoretical models for AlGaN strain relaxation of the S-K growth mode and critical thickness by considering the crucial role of threading dislocations (TDs) in releasing compressive stress. The experimentally measured critical thickness for three-dimensional growth was consistent with the calculated results. Furthermore, a crack-free high-quality 5 μm-thick Al_0.2Ga_0.8N template was successfully grown on an AlN/sapphire substrate.
- ultraviolet lasers,
- strain relaxation,
- critical thickness

Supplementary materials to this article can be found online at https://doi.org/10.1088/1674-4926/******.

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