Gallium Nitride and similar materials with wide band gaps and high critical fields are commonly used in power electronics. Integrating GaN-based materials in power electronics can improve device efficiency and lower electric power consumption. However, the lack of high-material quality gallium nitride impedes the advancement in gallium nitride high electron mobility transistors technology. The significant lattice mismatch between the AlN buffer layer leads to the formation of multiple strained layers with a high threading dislocation density as well as thermal boundary resistance affecting the device reliability. In this study, our objective is to fabricate a composite patterned graphene mask utilizing nitrogen-doped ultrananocrystalline diamond as a solid-state carbon source for graphene synthesis. The resulting composite graphene mask holds significant potential for application in epitaxial lateral overgrowth technology, leading to better crystal quality of GaN and improving the device's performance. This approach ensures high thermal stability but also mitigates threading dislocations caused due to lattice mismatch of GaN on sapphire substrate. The fabrication involved the homogeneous growth of a 250 nm nitrogen-doped ultrananocrystalline diamond on a sapphire substrate and using a nickel layer to convert it into graphene using a rapid thermal process. This graphene composite layer with low defects was converted into patterned composite graphene using a hard mask with a 30% masking rate as well as a photolithography technique with stripped and square patterned masks using 10%, 30% and 50% masking rates. The variation in the graphene patterns can be beneficial in improving the epitaxy of GaN. The Raman spectrum of the composite graphene layer reveals an ID/IG ratio of 0.3. Furthermore, scanning electron microscope validation attests to the successful attainment of a uniform graphene layer before its transformation into a patterned composite graphene mask. This composite graphene mask created with different masking rates can be used further for epitaxial lateral overgrowth technology.

References
[1] H. C. Yu et al., "Progress and prospects of GaN-based VCSEL from near UV to green emission," Progress in Quantum Electronics, Review vol. 57, pp. 1-19, 2018, doi: 10.1016/j.pquantelec.2018.02.001.
[2] Å. Haglund et al., Progress and challenges in electrically pumped GaN-based VCSELs. 2016, p. 98920Y.
[3] H.-Y. Ryu and J.-I. Shim, "Effect of current spreading on the efficiency droop of InGaN light-emitting diodes," Opt. Express, vol. 19, no. 4, pp. 2886-2894, 2011/02/14 2011, doi: 10.1364/OE.19.002886.
[4] M.-H. Kim et al., "Origin of efficiency droop in GaN-based light-emitting diodes," Applied Physics Letters, vol. 91, no. 18, 2007, doi: 10.1063/1.2800290.
[5] C. Hemmingsson, P. Paskov, G. Pozina, M. Heuken, B. Schineller, and B. Monemar, "Hydride vapor phase epitaxy growth and characterization of thick GaN using a vertical HVPE reactor," Journal of Crystal Growth, vol. 300, p. 32, 03/01 2007, doi: 10.1016/j.jcrysgro.2006.10.223.
[6] K. Motoki et al., "Growth and characterization of freestanding GaN substrates," Journal of Crystal Growth - J CRYST GROWTH, vol. 237, pp. 912-921, 04/01 2002, doi: 10.1016/S0022-0248(01)02078-4.
[7] J. X. Zhang, Y. Qu, Y. Z. Chen, A. Uddin, and S. Yuan, "Structural and optical characterization of GaN epilayers grown on Si(111) substrates by hydride vapor-phase epitaxy," Journal of Crystal Growth, vol. 282, no. 1, pp. 137-142, 2005/08/15/ 2005, doi: https://doi.org/10.1016/j.jcrysgro.2005.04.098.
[8] M. Leszczynski et al., "Comparison of Si, Sapphire, SiC, and GaN substrates for HEMT epitaxy," ECS Transactions, vol. 50, pp. 163-171, 03/20 2013, doi: 10.1149/05003.0163ecst.
[9] F. Roccaforte, Nitride Semiconductor Technology: Power Electronics and Optoelectronic Devices.
[10] L. Liu and J. H. Edgar, "Substrates for Gallium Nitride Epitaxy," Materials Science & Engineering R-reports - MAT SCI ENG R, vol. 37, pp. 61-127, 04/01 2002, doi: 10.1016/S0927-796X(02)00008-6.
[11] S. Nakamura, T. Mukai, and M. Senoh, "Candela‐class high‐brightness InGaN/AlGaN double‐heterostructure blue‐light‐emitting diodes," Applied Physics Letters, vol. 64, no. 13, pp. 1687-1689, 1994, doi: 10.1063/1.111832.
[12] Y. Zhao et al., "Optical properties evolution of GaN film grown via lateral epitaxial overgrowth," Applied Surface Science, vol. 513, p. 145816, 02/01 2020, doi: 10.1016/j.apsusc.2020.145816.
[13] Y. Kim et al., "Plasma-Enhanced Atomic Layer Deposition of SiN–AlN Composites for Ultra Low Wet Etch Rates in Hydrofluoric Acid," ACS Applied Materials & Interfaces, vol. 8, no. 27, pp. 17599-17605, 2016/07/13 2016, doi: 10.1021/acsami.6b03194.
[14] Y. Feng et al., "High quality GaN-on-SiC with low thermal boundary resistance by employing an ultrathin AlGaN buffer layer," Applied Physics Letters, vol. 118, no. 5, 2021, doi: 10.1063/5.0037796.
[15] K. W. Jang, I. T. Hwang, H. J. Kim, S. H. Lee, J. W. Lim, and H. S. Kim, "Thermal Analysis and Operational Characteristics of an AlGaN/GaN High Electron Mobility Transistor with Copper-Filled Structures: A Simulation Study," (in eng), Micromachines (Basel), vol. 11, no. 1, Dec 31 2019, doi: 10.3390/mi11010053.
[16] N. R. Jankowski, "GaN HEMT Junction Temperature Dependence on Diamond Substrate Anisotropy and Thermal Boundary Resistance."
[17] J.-T. Chen et al., "Low thermal resistance of a GaN-on-SiC transistor structure with improved structural properties at the interface," Journal of Crystal Growth, vol. 428, pp. 54-58, 2015/10/15/ 2015, doi: https://doi.org/10.1016/j.jcrysgro.2015.07.021.
[18] Y. Intelligence, " Market and Technology Trends Power GaN 2023." [Online]. Available: https://www.yolegroup.com/product/report/power-gan-2023/
[19] "Market analysis report." GVR-2-68038-848-0 (accessed.
[20] F. Roccaforte, G. Greco, P. Fiorenza, and F. Iucolano, "An Overview of Normally-Off GaN-Based High Electron Mobility Transistors," Materials, vol. 12, no. 10, p. 1599, 2019. [Online]. Available: https://www.mdpi.com/1996-1944/12/10/1599.
[21] Y. N. Picard et al., "Threading dislocation behavior in AlN nucleation layers for GaN growth on 4H-SiC," Applied Physics Letters, vol. 91, no. 1, 2007, doi: 10.1063/1.2754638.
[22] R. W. McClelland, C. O. Bozler, and J. C. C. Fan, "A technique for producing epitaxial films on reuseable substrates," Applied Physics Letters, vol. 37, pp. 560-562, 1980.
[23] F. Olsson, M. Xie, S. Lourdudoss, I. Prieto, and P. Postigo, "Epitaxial lateral overgrowth of InP on Si from nano-openings: Theoretical and experimental indication for defect filtering throughout the grown layer," Journal of Applied Physics, vol. 104, pp. 093112-093112, 12/01 2008, doi: 10.1063/1.2977754.
[24] S. Nakamura et al., "InGaN/GaN/AlGaN-Based Laser Diodes with Modulation-Doped Strained-Layer Superlattices," Japanese Journal of Applied Physics, vol. 36, p. L1568, 1997.
[25] M. Craven, S. Lim, F. Wu, J. Speck, and S. Denbaars, "Threading dislocation reduction via laterally overgrown nonpolar (110) a-plane GaN," Applied Physics Letters, vol. 81, pp. 1201-1203, 08/12 2002, doi: 10.1063/1.1498010.
[26] C. Johnston, M. Kappers, M. A. Moram, J. Hollander, and C. Humphreys, "Assessment of defect reduction methods for nonpolar a-plane GaN grown on r-plane sapphire," Journal of Crystal Growth, vol. 311, pp. 3295-3299, 06/01 2009, doi: 10.1016/j.jcrysgro.2009.03.044.
[27] C. Chen et al., "Lateral Epitaxial Overgrowth of Fully Coalesced A-Plane GaN on R-Plane Sapphire," Japanese Journal of Applied Physics, vol. 42, 06/15 2003, doi: 10.1143/JJAP.42.L640.
[28] X. Ni, U. Özgür, H. Morkoç, Z. Liliental-Weber, and H. Everitt, "Epitaxial lateral overgrowth of a-plane GaN by metalorganic chemical vapor deposition," Journal of Applied Physics, vol. 102, pp. 053506-053506, 09/06 2007, doi: 10.1063/1.2773692.
[29] T. Zheleva, O.-H. Nam, W. Ashmawi, J. Griffin, and R. Davis, "Lateral epitaxy and dislocation density reduction in selectively grown GaN structures," Journal of Crystal Growth, vol. 222, pp. 706-718, 02/01 2001, doi: 10.1016/S0022-0248(00)00832-0.
[30] S. Nakamura et al., "InGaN/GaN/AlGaN-based laser diodes with modulation-doped strained-layer superlattices grown on an epitaxially laterally overgrown GaN substrate," Applied Physics Letters, vol. 72, no. 2, pp. 211-213, 1998, doi: 10.1063/1.120688.
[31] J. B. Pushpendra Singh, Kaushik Pal, One-Step One Chemical Synthesis Process of Graphene from Rice Husk for Energy Storage Applications.
[32] Y. Zhao et al., "Optical properties evolution of GaN film grown via lateral epitaxial overgrowth," Applied Surface Science, vol. 513, p. 145816, 2020/05/30/ 2020, doi: https://doi.org/10.1016/j.apsusc.2020.145816.
[33] A. Kovács et al., "Graphoepitaxy of High-Quality GaN Layers on Graphene/6H–SiC," Advanced Materials Interfaces, vol. 2, no. 2, p. 1400230, 2015, doi: https://doi.org/10.1002/admi.201400230.
[34] J. J. Li et al., "Study on Nucleation and Growth Mode of GaN on Patterned Graphene by Epitaxial Lateral Overgrowth," (in English), Crystal Growth & Design, vol. 23, no. 8, pp. 5541-5547, Jun 28 2023, doi: 10.1021/acs.cgd.3c00171.
[35] Z. Y. Al Balushi et al., "The impact of graphene properties on GaN and AlN nucleation," Surface Science, vol. 634, pp. 81-88, 2015/04/01/ 2015, doi: https://doi.org/10.1016/j.susc.2014.11.020.
[36] J.-Y. Lee et al., "Multiple epitaxial lateral overgrowth of GaN thin films using a patterned graphene mask by metal organic chemical vapor deposition," Journal of Applied Crystallography, vol. 53, no. 6, pp. 1502-1508, 2020, doi: doi:10.1107/S1600576720012856.
[37] G. F. Yang et al., "InGaN/GaN multiple quantum wells on selectively grown GaN microfacets and the applications for phosphor-free white light-emitting diodes," Reviews in Physics, vol. 1, pp. 101-119, 2016/11/01/ 2016, doi: https://doi.org/10.1016/j.revip.2016.06.001.
[38] T. Zhang, Z. Xue, Y. Xie, G. Huang, and G. Peng, "Fabrication of a boron-doped nanocrystalline diamond grown on an WC-Co electrode for degradation of phenol," (in eng), RSC Adv, vol. 12, no. 41, pp. 26580-26587, Sep 16 2022, doi: 10.1039/d2ra04449h.
[39] S.-W. Kim, R. Takaya, S. Hirano, and M. Kasu, "Two-inch high-quality (001) diamond heteroepitaxial growth on sapphire (112̄0) misoriented substrate by step-flow mode," Applied Physics Express, vol. 14, no. 11, p. 115501, 2021/10/05 2021, doi: 10.35848/1882-0786/ac28e7.
[40] S. Handschuh-Wang, T. Wang, and Y. Tang, "Ultrathin Diamond Nanofilms—Development, Challenges, and Applications," Small, vol. 17, no. 30, p. 2007529, 2021, doi: https://doi.org/10.1002/smll.202007529.
[41] O. A. Williams, "Nanocrystalline diamond," Diamond and Related Materials, vol. 20, no. 5-6, pp. 621-640, 2011.
[42] P. W. May, N. L. Allan, M. N. R. Ashfold, J. C. Richley, and Y. A. Mankelevich, "Simplified Monte Carlo simulations of chemical vapour deposition diamond growth," Journal of Physics: Condensed Matter, vol. 21, no. 36, p. 364203, 2009/08/19 2009, doi: 10.1088/0953-8984/21/36/364203.
[43] N. Yang et al., "Conductive diamond: synthesis, properties, and electrochemical applications," Chemical Society Reviews, 10.1039/C7CS00757D vol. 48, no. 1, pp. 157-204, 2019, doi: 10.1039/C7CS00757D.
[44] T. Hara et al., "Ultrananocrystalline diamond prepared by pulsed laser deposition," Diamond and Related Materials, vol. 15, no. 4, pp. 649-653, 2006/04/01/ 2006, doi: https://doi.org/10.1016/j.diamond.2005.12.015.
[45] D. Pradhan and I. N. Lin, "Effect of titanium powder assisted surface pretreatment process on the nucleation enhancement and surface roughness of ultrananocrystalline diamond thin films," Applied Surface Science, vol. 255, no. 15, pp. 6907-6913, 2009/05/15/ 2009, doi: https://doi.org/10.1016/j.apsusc.2009.03.013.
[46] S. Yugo, N. Ishigaki, K. Hirahara, J. Sano, T. Sone, and T. Kimura, "Effects of bias voltage on microwave plasma used for diamond growth," Diamond and Related Materials, vol. 8, no. 8, pp. 1406-1409, 1999/08/01/ 1999, doi: https://doi.org/10.1016/S0925-9635(99)00021-7.
[47] A. Saravanan, B.-R. Huang, K. J. Sankaran, N.-H. Tai, and I. N. Lin, "Highly Conductive Diamond–Graphite Nanohybrid Films with Enhanced Electron Field Emission and Microplasma Illumination Properties," ACS Applied Materials & Interfaces, vol. 7, no. 25, pp. 14035-14042, 2015/07/01 2015, doi: 10.1021/acsami.5b03166.
[48] A. Saravanan, B. R. Huang, K. J. Sankaran, C. L. Dong, N. H. Tai, and I. N. Lin, "Fast growth of ultrananocrystalline diamond films by bias-enhanced nucleation and growth process in CH4/Ar plasma," Applied Physics Letters, vol. 104, no. 18, 2014, doi: 10.1063/1.4875808.
[49] W. Yuan et al., "Highly conductive nitrogen-doped ultrananocrystalline diamond films with enhanced field emission properties: triethylamine as a new nitrogen source," Journal of Materials Chemistry C, 10.1039/C6TC00087H vol. 4, no. 21, pp. 4778-4785, 2016, doi: 10.1039/C6TC00087H.
[50] J. Shalini et al., "Ultra-nanocrystalline diamond nanowires with enhanced electrochemical properties," Electrochimica Acta, vol. 92, pp. 9-19, 2013/03/01/ 2013, doi: https://doi.org/10.1016/j.electacta.2012.12.078.
[51] M. Yi and Z. Shen, "A review on mechanical exfoliation for the scalable production of graphene," Journal of Materials Chemistry A, vol. 3, no. 22, pp. 11700-11715, 2015.
[52] Z. Yan et al., "Growth of Bilayer Graphene on Insulating Substrates," ACS Nano, vol. 5, no. 10, pp. 8187-8192, 2011/10/25 2011, doi: 10.1021/nn202829y.
[53] L. I. U. P.-P. S. U. N. L.-L. K. E. P.-L. C. U. I. P. W. A.-Y. Li Han-Chao, "Recent Development of the Transformation from Amorphous Carbon to Graphene Method <i>via</i> Metal Catalyst," Journal of Inorganic Materials, vol. 33, no. 6, pp. 587-595, 2018. [Online]. Available: {https://www.jim.org.cn/EN/10.15541/jim20170527}.
[54] C. Chen et al., "Low-Defect Nanodiamonds and Graphene Nanoribbons Enhanced Electron Field Emission Properties in Ultrananocrystalline Diamond Films," ACS Applied Electronic Materials, vol. 3, no. 4, pp. 1648-1655, 2021/04/27 2021, doi: 10.1021/acsaelm.0c01111.
[55] C. Chih, "Preparation of Graphene/Nitrogen-Doped Ultrananocrystalline Diamond Hybrid Electrode for Gallium Nitride High Electron Mobility Transistors," Masters, Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei, M11004215, 2023.