Direct growth of high-quality GaN on single-crystal AlN substrate and related thermal characterization

Yinghao Chen; Hongcai Li; Genhao Liang; Zhengguang Fang; Jun Zhang; Kai Wang; Jiayu Dai; Xiaoxiang Yu; Lishan Zhao

doi:10.1088/1674-4926/25120047

J. Semicond. > Just Accepted

ARTICLES

Direct growth of high-quality GaN on single-crystal AlN substrate and related thermal characterization

Yinghao Chen^{1, §}, Hongcai Li^{2, §}, Genhao Liang^{1, §}, Zhengguang Fang¹, Jun Zhang¹, Kai Wang³, Jiayu Dai², Xiaoxiang Yu^2, and Lishan Zhao^1,

+ Author Affiliations

1. College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China
2. College of Science, National University of Defense Technology, Changsha 410073, China
3. Hunan Institute of Advanced Technology, Changsha 410205, China
^§Yinghao Chen, Hongcai Li and Genhao Liang contributed equally to this work and should be considered as co-first authors.

Author Bio:

Yinghao Chen is pursuing a Ph.D. degree with the College of Advanced Interdisciplinary Studies, National University of Defense Technology. His research focuses on wide-bandgap semiconductor and device electro-thermal co-simulation.

Hongcai Li got his BS from Hunan Normal University. Now he is an MS student at the National University of Defense Technology under the supervision of Assoc. Prof. Xiaoxiang Yu. His research focuses on micro-and nanoscale heat transfer and experimental thermal measurement.

Genhao Liang received the Ph.D. degree from University of Science and Technology of China in 2024. He now is post-doctora of National University of Defense Technology. His research interests include wide-bandgap and ultra-wide-bandgap semiconductor materials and devices.

Xiaoxiang Yu got his BS degree in 2012 and PhD degree in 2020 from Huazhong University of Science and Technology. Then he joined the National University of Defense Technology as an associate professor. His research interests include micro- and nanoscale heat transfer and thermal management.

Lishan Zhao received his B.Sc.degree in Opto-electric Engineering from the National University of Defense Technology, Changsha, China, in 2009, and the Ph.D.degree in Condensed Matter Physics from the University of St Andrews, St Andrews, U.K., in 2016. He has been working at the National University of Defense Technology since 2016, where he is now an Associate Scientist at the College of Advanced Interdisciplinary Studies. His main research interest lies in wide and ultra-wide band-gap semiconductors, microwaves, power electronics and condensed matter physics.

Corresponding author: Xiaoxiang Yu, xxyu@nudt.edu.cn; Lishan Zhao, lishanzhao@nudt.edu.cn

DOI: 10.1088/1674-4926/25120047CSTR: 32376.14.1674-4926.25120047

Abstract: Bulk single-crystal aluminum nitride (BSC AlN) substrates are known to be ideal platforms for constructing high-power and DUV optoelectronic nitride devices. However, high-quality epitaxial growth of nitride films on BSC AlN and related characterization is still far from being well studied. The challenges and uncertainties in doing accurate thermal characterization on such heterostructures are not fully recognized. In this study, we successfully fabricated a buffer-free thin GaN/AlN heterostructure on a BSC AlN substrate via metal-organic chemical vapor deposition (MOCVD) technology. This heterostructure consists of a 140 nm-thick AlN homoepitaxial layer and a 480 nm-thick GaN epitaxial layer. Characterization results indicate that the prepared heterojunction has excellent crystal quality and smooth surface morphology. To accurately obtain the thermophysical parameters of the heterostructure, this study employed broadband frequency domain thermoreflectance (BB-FDTR) technology, and careful measurements with detailed data analysis were demonstrated. In addition to showing the feasibility of epitaxial growth of high-quality thin film GaN directly on BSC AlN substrates, this study also provides key experimental data for evaluating the heat dissipation advantages of GaN/AlN heterostructures.

Key words: single-crystal AlN substrate, GaN/AlN heterostructure, broadband frequency domain thermoreflectance, thermal properties

References

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Fig. 1. (Color online) (a) TEM schematic diagram of the cross-section of GaN/AlN heterostructure. The Al and Pt in the figure are required for thermal testing and slicing. (b) STEM image at the GaN/AlN interface. (c) STEM image at the AlN/AlN interface. (d) Atomic resolution image of the GaN region marked in (b). (e) Atomic resolution image of the AlN region marked in (b).

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Fig. 2. (Color online) RSM characterization across the asymmetric (−105) plane of the GaN/AlN heterostructure.

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Fig. 3. (Color online) Two types of AFM images of GaN/AlN heterostructure: (a) the optical detection mode and (b) tapping mode.

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Fig. 4. (Color online) XRD rocking curve image of the GaN/AlN heterostructure.

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Fig. 5. (Color online) The FWHM of the XRD (002) plane as a function of GaN channel thickness from this work (star) and previous reports from Ref. [12, 22−29]. Among them, Ref. [12] is an AlN substrate, and Ref. [22−29] is a SiC substrate.

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Fig. 6. (Color online) Schematic diagram of (a) the overall thermal measurement state, (b) back measurement of AlN thermal conductivity, and (c) front measurement of thermal properties of GaN/AlN heterojunction.

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Fig. 7. (Color online) (a) Phase fitting curve of Al/AlN structure. The blue and green dashed lines represent the ±25% deviation curves of the thermal conductivity of AlN. (b) Sensitivity curve of the Al/AlN structure. The curve reveals that the sensitivity for both thermal conductivity and volumetric heat capacity remains high over the entire employed frequency range.

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Fig. 8. (Color online) (a) Phase fitting curve of the Al/GaN/AlN trilayer structure. Owing to the use of the high-frequency range for independently fitting the thermal conductivity of GaN, the corresponding ±25% curves are not plotted. (b) Sensitivity curves for the Al/GaN/AlN trilayer structure. Both the thermal conductivity and the volumetric heat capacity of GaN and AlN exhibit consistently high sensitivity across the entire frequency range used.

DownLoad: Full-Size Img PowerPoint

[1]	Pinto R M R, Gund V, Dias R A, et al. CMOS-integrated aluminum nitride MEMS: A review. J Microelectromech Syst, 2022, 31(4): 500 doi: 10.1109/JMEMS.2022.3172766
[2]	Kogut I, Hartmann C, Gamov I, et al. Electromechanical losses in carbon- and oxygen-containing bulk AlN single crystals. Solid State Ion, 2019, 343: 115072 doi: 10.1016/j.ssi.2019.115072
[3]	Kobayashi H, Sato K, Okuaki Y, et al. Enhanced wall-plug efficiency over 2.4% and wavelength dependence of electrical properties at far UV-C light-emitting diodes on single-crystal AlN substrate. Phys Status Solidi RRL, 2024, 18(11): 2400002
[4]	Kobayashi H, Sato K, Okuaki Y, et al. Milliwatt-power sub-230-nm AlGaN LEDs with >1500 h lifetime on a single-crystal AlN substrate with many quantum wells for effective carrier injection. Appl Phys Lett, 2023, 122(10): 101103 doi: 10.1063/5.0139970
[5]	Majkić A, Franke A, Kirste R, et al. Optical nonlinear and electro-optical coefficients in bulk aluminium nitride single crystals. Phys Status Solidi B:, 2017, 254(9): 1700077 doi: 10.1002/pssb.201700077
[6]	Senichev A, Martin Z O, Wang Y Q, et al. Quantum emitters in aluminum nitride induced by heavy ion irradiation. APL Quantum, 2024, 1(3): 036103 doi: 10.1063/5.0199647
[7]	Ozaki S, Yaita J, Yamada A, et al. First demonstration of X-band AlGaN/GaN high electron mobility transistors using free-standing AlN substrate over 15 W mm^–1 output power density. Appl Phys Express, 2021, 14(4): 041004 doi: 10.35848/1882-0786/abec90
[8]	Kotani J, Yaita J, Homma K, et al. 24.4 W/mm X-band GaN HEMTs on AlN substrates with the LPCVD-grown high-breakdown-field SiN_x layer. IEEE J Electron Devices Soc, 2023, 11: 101 doi: 10.1109/JEDS.2023.3234235
[9]	Wolf M, Brunner F, Last C, et al. 1.17 GW/cm² AlN-based GaN-channel HEMTs on mono-crystalline AlN substrate. IEEE Electron Device Lett, 2024, 45(6): 1048 doi: 10.1109/LED.2024.3391397
[10]	Elwaradi R, Mehta J, Ngo T H, et al. Effects of GaN channel downscaling in AlGaN–GaN high electron mobility transistor structures grown on AlN bulk substrate. J Appl Phys, 2023, 133(14): 145705 doi: 10.1063/5.0147048
[11]	Kim E, Chen Y H, Pieczulewski N, et al. XHEMTs on ultrawide bandgap single-crystal AlN substrates. Adv Electron Mater, 2026, 12(3): e00393 doi: 10.1002/aelm.202500393
[12]	Kim M, Papamichail A, Tran D Q, et al. Thin-channel AlGaN/GaN/AlN double heterostructure HEMTs on AlN substrates via hot-wall MOCVD. Appl Phys Lett, 2025, 127(3): 032104 doi: 10.1063/5.0282836
[13]	Mitterhuber L, Hammer R, Dengg T, et al. Thermal characterization and modelling of AlGaN-GaN multilayer structures for HEMT applications. Energies, 2020, 13(9): 2363 doi: 10.3390/en13092363
[14]	Norman L R, Abdallah Z, Pomeroy J W, et al. Impact of AlGaN back barrier on the thermal resistance of RF HEMTs. IEEE Electron Device Lett, 2025, 46(7): 1047 doi: 10.1109/LED.2025.3572287
[15]	Yang T, Hao H F, Yin Y C, et al. Dislocation evolution along the growth direction of 2-inch GaN crystal grown by Na-flux LPE. Mater Sci Semicond Process, 2021, 126: 105684 doi: 10.1016/j.mssp.2021.105684
[16]	Ma X, Wang K, Chen J X, et al. Optimal thermal resistance model of GaN HEMTs considering thickness-dependent thermal conductivity. IEEE Trans Electron Devices, 2024, 71(12): 7326 doi: 10.1109/TED.2024.3474610
[17]	Regner K T, Sellan D P, Su Z H, et al. Broadband phonon mean free path contributions to thermal conductivity measured using frequency domain thermoreflectance. Nat Commun, 2013, 4: 1640 doi: 10.1038/ncomms2630
[18]	Ziade E. Wide bandwidth frequency-domain thermoreflectance: Volumetric heat capacity, anisotropic thermal conductivity, and thickness measurements. Rev Sci Instrum, 2020, 91(12): 124901 doi: 10.1063/5.0021917
[19]	Li H C, Zhang E R, Duan S J, et al. Experimental evidence of impurity-induced selective short-mean-free-path phonon scatterings in β-Ga₂O₃. Appl Phys Lett, 2025, 127(13): 132202 doi: 10.1063/5.0293469
[20]	Wang J B, Li X D, Cheng Z B, et al. Suppressing the leakage of GaN HEMTs on single-crystalline AlN templates by buffer optimization. IEEE Trans Electron Devices, 2024, 71(11): 6609 doi: 10.1109/TED.2024.3466841
[21]	Yao Y X, Huang S, Cao R Y, et al. Dislocation-assisted electron and hole transport in GaN epitaxial layers. Nat Commun, 2025, 16: 6448 doi: 10.1038/s41467-025-61510-w
[22]	Im K S, Kim M, Nam O. Device and noise performances of AlGaN/GaN high electron mobility transistors with various GaN channel layers grown on AlN buffer layer. Phys Status Solidi A, 2024, 221(21): 2400014 doi: 10.1002/pssa.202400014
[23]	Zhang H F, Chen J T, Papamichail A, et al. Effect of substrate misorientation angle on the structural properties of N-polar GaN grown by hot-wall MOCVD on 4H-SiC(0001̄). J Cryst Growth, 2025, 651: 127971 doi: 10.1016/j.jcrysgro.2024.127971
[24]	Li C H, Li Z H, Peng D Q, et al. Growth of thin AlN nucleation layer and its impact on GaN-on-SiC heteroepitaxy. J Alloys Compd, 2020, 838: 155557 doi: 10.1016/j.jallcom.2020.155557
[25]	Zhang D G, Li Z H, Yang Q K, et al. Research on epitaxial of 250 nm high quality GaN HEMT based on AlN surface leveling technology. Appl Surf Sci, 2020, 509: 145339 doi: 10.1016/j.apsusc.2020.145339
[26]	Pandey A, Singh V K, Dalal S, et al. Effect of two step GaN buffer on the structural and electrical characteristics in AlGaN/GaN heterostructure. Vacuum, 2020, 178: 109442 doi: 10.1016/j.vacuum.2020.109442
[27]	Yang Y, Ni X F, Fan Q, et al. Study of low-temperature (Al)GaN on N-polar GaN films grown by MOCVD on vicinal SiC substrates. Materials, 2025, 18(3): 638 doi: 10.3390/ma18030638
[28]	Chen D Y, Wen K H, Thorsell M, et al. Impact of the channel thickness on electron confinement in MOCVD-grown high breakdown buffer-free AlGaN/GaN heterostructures. Phys Status Solidi A, 2023, 220(16): 2200496 doi: 10.1002/pssa.202200496
[29]	Chang K P, Lin P J, Horng R H, et al. Growth characteristics of Fe-doped GaN epilayers on SiC (001) substrates and their effects on high breakdown voltage devices. Mater Sci Semicond Process, 2020, 119: 105228 doi: 10.1016/j.mssp.2020.105228
[30]	Slack G A, Tanzilli R A, Pohl R O, et al. The intrinsic thermal conductivity of AIN. J Phys Chem Solids, 1987, 48(7): 641 doi: 10.1016/0022-3697(87)90153-3
[31]	Levinshtein M E, Rumyantsev S L, Shur M S. Properties of advanced semiconductor materials: GaN, AlN, InN, BN, SiC, SiGe. New York: Wiley, 2001
[32]	Zhang Y Y, Su Q, Zhu J, et al. Thickness-dependent thermal conductivity of mechanically exfoliated β-Ga₂O₃ thin films. Appl Phys Lett, 2020, 116(20): 202101 doi: 10.1063/5.0004984
[33]	Walwil H, Song Y W, Shoemaker D C, et al. Thermophysical property measurement of GaN/SiC, GaN/AlN, and AlN/SiC epitaxial wafers using multi-frequency/spot-size time-domain thermoreflectance. J Appl Phys, 2025, 137(9): 095105 doi: 10.1063/5.0245381
[34]	Li G W, Song B, Ganguly S, et al. Two-dimensional electron gases in strained quantum wells for AlN/GaN/AlN double heterostructure field-effect transistors on AlN. Appl Phys Lett, 2014, 104(19): 193506 doi: 10.1063/1.4875916
[35]	Chen S T, Chen Q S, Ye F, et al. Epitaxial growth of a high-quality GaN/AlN heterostructure for the development of an AlN-back barrier high-electron-mobility-transistor. CrystEngComm, 2025, 27(23): 4011 doi: 10.1039/D5CE00205B
[36]	Cheng J P, Yang X L, Sang L, et al. High mobility AlGaN/GaN heterostructures grown on Si substrates using a large lattice-mismatch induced stress control technology. Appl Phys Lett, 2015, 106(14): 142106 doi: 10.1063/1.4917504
[37]	Hartmann C, Dittmar A, Wollweber J, et al. Bulk AlN growth by physical vapour transport. Semicond Sci Technol, 2014, 29(8): 084002 doi: 10.1088/0268-1242/29/8/084002
[38]	Cahill D G. Thermal conductivity measurement from 30 to 750 K: The 3ω method. Rev Sci Instrum, 1990, 61(2): 802 doi: 10.1063/1.1141498
[39]	Wang Z L, Tang D W, Zheng X H. Simultaneous determination of thermal conductivities of thin film and substrate by extending 3ω-method to wide-frequency range. Appl Surf Sci, 2007, 253(22): 9024 doi: 10.1016/j.apsusc.2007.05.020
[40]	Chernodubov D A, Bondareva Y V, Shibalov M V, et al. Measurement of the thermal conductivity of carbon nanowalls by the 3ω method. Jetp Lett, 2023, 117(6): 449 doi: 10.1134/S0021364023600313
[41]	Tanisawa D, Shionozaki Y, Takizawa T, et al. Ultralow thermal conductivity of amorphous silicon–germanium thin films for alloy and disorder scattering determined by 3ω method and nanoindentation. Appl Phys Express, 2024, 17(1): 011005 doi: 10.35848/1882-0786/ad14f1
[42]	Wilson R B, Cahill D G. Anisotropic failure of Fourier theory in time-domain thermoreflectance experiments. Nat Commun, 2014, 5: 5075 doi: 10.1038/ncomms6075
[43]	Hu Y J, Zeng L P, Minnich A J, et al. Spectral mapping of thermal conductivity through nanoscale ballistic transport. Nat Nanotechnol, 2015, 10(8): 701 doi: 10.1038/nnano.2015.109
[44]	Kang J S, Li M, Wu H, et al. Experimental observation of high thermal conductivity in boron arsenide. Science, 2018, 361(6402): 575 doi: 10.1126/science.aat5522
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Received: 26 December 2025 Revised: 23 February 2026 Online: Accepted Manuscript: 12 March 2026

Article Navigation > Journal of Semiconductors > 2026 > Accepted Manuscript

Yinghao Chen, Hongcai Li, Genhao Liang, Zhengguang Fang, Jun Zhang, Kai Wang, Jiayu Dai, Xiaoxiang Yu, Lishan Zhao. Direct growth of high-quality GaN on single-crystal AlN substrate and related thermal characterization[J]. Journal of Semiconductors, 2026, In Press. doi: 10.1088/1674-4926/25120047 ****Y H Chen, H C Li, G H Liang, Z G Fang, J Zhang, K Wang, J Y Dai, X X Yu, and L S Zhao, Direct growth of high-quality GaN on single-crystal AlN substrate and related thermal characterization[J]. J. Semicond., 2026, accepted doi: 10.1088/1674-4926/25120047

Citation:

Y H Chen, H C Li, G H Liang, Z G Fang, J Zhang, K Wang, J Y Dai, X X Yu, and L S Zhao, Direct growth of high-quality GaN on single-crystal AlN substrate and related thermal characterization[J]. J. Semicond., 2026, accepted doi: 10.1088/1674-4926/25120047

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Direct growth of high-quality GaN on single-crystal AlN substrate and related thermal characterization

DOI: 10.1088/1674-4926/25120047

CSTR: 32376.14.1674-4926.25120047

1.
College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China
2.
College of Science, National University of Defense Technology, Changsha 410073, China
3.
Hunan Institute of Advanced Technology, Changsha 410205, China

More Information

Yinghao Chen is pursuing a Ph.D. degree with the College of Advanced Interdisciplinary Studies, National University of Defense Technology. His research focuses on wide-bandgap semiconductor and device electro-thermal co-simulation
Hongcai Li got his BS from Hunan Normal University. Now he is an MS student at the National University of Defense Technology under the supervision of Assoc. Prof. Xiaoxiang Yu. His research focuses on micro-and nanoscale heat transfer and experimental thermal measurement
Genhao Liang received the Ph.D. degree from University of Science and Technology of China in 2024. He now is post-doctora of National University of Defense Technology. His research interests include wide-bandgap and ultra-wide-bandgap semiconductor materials and devices
Xiaoxiang Yu got his BS degree in 2012 and PhD degree in 2020 from Huazhong University of Science and Technology. Then he joined the National University of Defense Technology as an associate professor. His research interests include micro- and nanoscale heat transfer and thermal management
Lishan Zhao received his B.Sc.degree in Opto-electric Engineering from the National University of Defense Technology, Changsha, China, in 2009, and the Ph.D.degree in Condensed Matter Physics from the University of St Andrews, St Andrews, U.K., in 2016. He has been working at the National University of Defense Technology since 2016, where he is now an Associate Scientist at the College of Advanced Interdisciplinary Studies. His main research interest lies in wide and ultra-wide band-gap semiconductors, microwaves, power electronics and condensed matter physics
Corresponding author: xxyu@nudt.edu.cn; lishanzhao@nudt.edu.cn
Received Date: 2025-12-26
Revised Date: 2026-02-23

Available Online: 2026-03-12

Abstract

Abstract

Bulk single-crystal aluminum nitride (BSC AlN) substrates are known to be ideal platforms for constructing high-power and DUV optoelectronic nitride devices. However, high-quality epitaxial growth of nitride films on BSC AlN and related characterization is still far from being well studied. The challenges and uncertainties in doing accurate thermal characterization on such heterostructures are not fully recognized. In this study, we successfully fabricated a buffer-free thin GaN/AlN heterostructure on a BSC AlN substrate via metal-organic chemical vapor deposition (MOCVD) technology. This heterostructure consists of a 140 nm-thick AlN homoepitaxial layer and a 480 nm-thick GaN epitaxial layer. Characterization results indicate that the prepared heterojunction has excellent crystal quality and smooth surface morphology. To accurately obtain the thermophysical parameters of the heterostructure, this study employed broadband frequency domain thermoreflectance (BB-FDTR) technology, and careful measurements with detailed data analysis were demonstrated. In addition to showing the feasibility of epitaxial growth of high-quality thin film GaN directly on BSC AlN substrates, this study also provides key experimental data for evaluating the heat dissipation advantages of GaN/AlN heterostructures.
- single-crystal AlN substrate,
- GaN/AlN heterostructure,
- broadband frequency domain thermoreflectance,
- thermal properties

^§Yinghao Chen, Hongcai Li and Genhao Liang contributed equally to this work and should be considered as co-first authors.

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