下世代微發光二極體(Micro LED)顯示技術為追求更高解析度，LED晶粒需大幅縮小，然而當晶粒尺寸微縮時，亮度也隨之降低，增加注入電流維持顯示所需足夠亮度為最快解決方法。目前LED使用之氧化銦錫透明導電層熱傳導率偏低，大電流注入下易造成元件熱衰退。石墨烯具有高熱傳導率與高電子遷移率，加上單層石墨烯穿透率高達95%，適合作為電極材料。傳統以轉貼方式將銅箔上石墨烯轉貼至LED元件上，此方法製備石墨烯電極易產生貼合不良、折皺或破裂問題，本研究初期利用氮摻雜超奈米晶鑽石(N-UNCD)薄膜作為製備石墨烯所需碳源，配合金屬鎳催化層之熱處理轉換技術，成功在圖案化藍寶石基板上直接成長石墨烯。透過拉曼光譜量測，為多層石墨烯薄膜。進一步在多層石墨烯薄膜上蒸鍍金屬鎳，經變溫電流電壓(I-V-T)量測結果顯示多層石墨烯呈現正電阻溫度係數特性。
本論文進一步在LED晶圓上調整金屬鎳催化層與N-UNCD厚度分別為
200/350 nm，經過700度熱處理與自然降溫步驟後，在使用酸液去除殘餘鎳金屬步驟中，我們發現N-UNCD隨著鎳層一起從LED晶圓上剝落，猜測可能為碳在700度熱處理過程中往上溶進鎳層，鎳層往下並堆積在LED表面，成為LED表面轉換石墨烯之金屬催化層，當LED表面石墨烯形成後，因其微弱凡德瓦爾力無法拉住上面N-UNCD，導致N-UNCD與殘留鎳層一起剝落。利用此技術本研究成功在LED晶圓上製備多層石墨烯電極，電致發光光譜顯示發光譜峰為469 nm。

In order to improve the resolution of the next generation of micro-LED display technology, the reduction of chip size is well known a useful approach. However, the issue generated from decrease of chip size decreases the emitting intensity of LED significantly. Increasing injection current of LED chip can increase the emitting intensity effectively. Currently, the ITO was used in GaN based LED as transparency conductive layer. Unfortunately, the poor thermal conductivity of ITO degenerate the LED’s performance especially for a high injection current. The graphene exhibits a high electron mobility and high thermal conductivity that is a promising material for electrode application in GaN based LED. In general, the electrode on LED using transfer graphene technique will generate wrinkle and/or cracking, resulted a poor stability of electrical property. In this study, the nitrogen-doped ultrananocrystalline diamond thin-film was deposited on nanopatterned sapphire substrate (NPSS) as a solid carbon dopant source. Combined the metal Ni catalyst technique, the multi-layer graphene can be obtained on NPSS which confirmed by Raman spectrum. In addition, the IVT characteristics of multi-layer graphene exhibit a positive temperature coefficient of resistance.
In addition, the optimal thicknesses of Ni/N-UNCD (i.e. 200/350 nm) were grown on LED with 700 oC thermal process in 20 minutes. After finish the cooling process, the residual Ni layer on LED was removed by acid etching process. It is interesting that not only the residual Ni layer but also N-UNCD layer were peeled off from LED surface. The Raman spectrum indicated that a multi-layer graphene layer is generated on the LED surface. The electroluminescence spectrum shows an emitting peak at 469 nm for LED with a multi-layer graphene electrode.
 

[1]. K. Singh, A. Chauhan, M. Mathew, R. Punia, R. S. Kundu, Effects on electrical and optical properties of InGaN/GaN MQWs light-emitting diodes using Ni/ITO transparent p-contacts on p-GaN, J Opt., 48 (2019) 240.
[2]. Y. J. Liu, C. C. Huang, T. Y. Chen, C. S. Hsu, J. K. Liou, T. Y. Tsai, W. C. Liu, Implementation of an indium-tin-oxide (ITO) direct-Ohmic contact structure on a GaN-based light emitting diode, Opt. Express., 19 (2011) 14662.
[3]. H. Ahmad, H. Ali, Z. Hassan, A. Shuhaimi, Enhancement of optical transmittance and electrical resistivity of post-annealed ITO thin films RF sputtered on Si, Appl. Surf. Sci., 443 (2018) 544.
[4]. R.I.M. Asri, N.A. Hamzah, M.A. Ahmad, M.Ikram Md Taib, S.M.S. Sahil, Z. Hassan, Role of RF Magnetron Sputtering Power on Optical and Electrical Properties of ITO Films on Soda-Lime Glass Substrates , J. Phys. Conf. Ser., 1535 (2020) 012035.
[5]. Hernando, S. Q. Lud, P. Bruno, G. M. Gruen, M. Stutzmannand, J. A. Garrido, Electrochemical impedance spectroscopy of oxidized and hydrogen-terminated nitrogen-induced conductive ultrananocrystalline diamond, Electrochim. Acta., 54 (2009) 1909.
[6]. R. Arenal, O. Stephan, P. Bruno and D. M. Gruen, Spatially resolved electron energy lossspectroscopy on n-type ultrananocrystallinediamond films, Appl. Phys.Lett., 94 (2009) 111905.
[7]. J. Birrell, J. E. Gerbi, O. Auciello, J. M. Gibson, D. M. Gruenand J. A. Carlisle,J, Bonding structure in nitrogen doped ultrananocrystalline diamond, Appl. Phys. Lett., 93 (2003) 5606.
[8]. I. Vlasov, V. G. Ralchenko, E. Goovaerts, A. V. SavelievM. V. Kanzyuba, Bulk and surface-enhanced Raman spectroscopy of nitrogen-doped ultrananocrystalline diamond films, Phys. Status Solidi A., 203 (2006) 3028.
[9]. W. Yuan, L. P. Fang, Z. Feng, Z. X. Chen, J. W. Wen, Y. Xiong, B. Wang, Highly conductive nitrogen-doped ultrananocrystalline diamond films with enhanced field emission properties: triethylamine as a new nitrogen source, J. Mater. Chem. C., 4 (2016) 4778.
[10]. Y. H. Tzeng, S. P. Yeh, W. C. Fang, Y. C. Chu, Nitrogen-incorporated ultrananocrystalline diamond and multi-layer-graphene-like hybrid carbon films, Sci. Rep., 4 (2014) 4531.
[11]. S. Bhattacharyya, O. Auciello, J. Birrell, J. A. Carlisle, L. A. Curtiss, A. N. Goyette, D. M. Gruen, A. R. Krauss, J. Schlueter, A. Sumant, P. Zapol, Synthesis and characterization of highly-conducting nitrogen-doped ultrananocrystalline diamond films, Appl. Phys. Lett., 79 (2001) 1441.
[12]. W. C. Ke, C. Y. Chiang, T. G. Kim, Y. C. Lin, C. Y. Liao, K. J. Chang, J. C. Lin, Nitrogen doped ultrananocrystalline diamond conductive layer grown on InGaN-based light-emitting diodes using nanopattern enhanced nucleation, Appl. Surf. Sci., 546 (2021) 149052.
[13]. M. R. Habib, T. Liang, X. G. Yu, X. D. Pi, Y. C. Liu , M. S. Xu, A review of theoretical study of graphene chemical vapor deposition synthesis on metals: nucleation, growth, and the role of hydrogen and oxygen, Rep. Prog. Phys., 81 (2018) 36501.
[14]. M. Losurdo, M. M. Giangregorio, P. Capezzuto, G. Bruno, Graphene CVD growth on copper and nickel: role of hydrogen in kinetics and structure, Phys. Chem. Chem. Phys., 13 (2011) 20836.
[15]. X. Li, W. Cai, L. Colombo, R. S. Ruoff, Evaloution of graphene growth on Ni and Cu by carbon isotope labelling, Nano lett., 9 (2009) 4268.
[16]. S.Y. Kwon, C.V. Ciobanu, V. Petrova, V.B. Shenoy, J. Bareno, V. Gambin, I. Petrov, S. Kodambaka, Growth of semiconducting graphene on palladium, Nano Lett., 9 (2009) 3985.
[17]. A.E. Morgan, G.A. Somorjai, Low energy electron diffraction studies of gas adsorption on the platinum (100) single crystal surface, Surface Science., 12 (1968) 405.
[18]. Mingguang Chen, Robert C. Haddon ab, Ruoxue Yan, Elena Bekyarova, Advances in transferring chemical vapour deposition graphene: a review, Mater. Horiz., 4 (2017) 1054.
[19]. A. Hussain, S. M. Mehdi, N. Abbas, M. Hussain, R. A. N. Qvi, Synthesis of Graphene from Solid Carbon Sources: A focused review, Mater. Chem. Phys., 248 (2020) 122924.
[20]. S. W. Feng, Y. H. Wang, C. Y. Tsai, T. H. Cheng, H. C. Wang, Enhancing carrier transport and carrier capture with a good current spreading characteristic via graphene transparent conductive electrodes in InGaN/GaN multiple-quantum-well light emitting diodes, Sci. Rep., 10 (2020) 10539.
[21]. Z. Peng, Z. Yan, Z. Z. Sun, J. M. Tour, Direct Growth of Bilayer Graphene on SiO2 Substrates by Carbon Diffusion through Nickel, ACS Sens., 5 (2011) 8241.
[22]. M. Zheng, K. Takei, B. Hsia, H. Fang, X. Zhang, N. Ferralis, H. Ko, Y. L. Chueh, Y. Zhang, R. Maboudian, A. Javey, Metal-catalyzed crystallization of amorphous carbon to graphene, Appl. Phys. Lett., 96 (2010) 063110.
[23]. L. C. Guo, Z. Y. Zhang, H. Y. Sun, D. Dai, J. F. Cui, M. Z. Lia, Y. Xu, M. S. Xu, Y. F. Du, N. Jiang, F. Huang, C.T. Lin, Direct formation of wafer-scale single-layer graphene films on the rough surface substrate by PECVD, Carbon., 129 (2018) 456.
[24]. H. Murata, K. Toko, N. Saitoh, N. Yoshizawa, T. Suemasu, Direct synthesis of multilayer graphene on an insulator by Ni-induced layer exchange growth of amorphous carbon, Appl. Phys. Lett., 110 (2017) 033108.
[25]. Z. Wang, L. Gu, L. P. H. Jeurgens, F. Phillipp, E. J. Mittemeijer, Real-Time Visualization of Convective Transportation of Solid Materials at Nanoscale, Nano.Lett., 12 (2012) 6126.
[26]. H. Murata, K. Toko, and T. Suemasu, High-quality multilayer graphene on an insulator formed by diffusion controlled Ni-induced layer exchange, Appl. Phys. Lett., 111 (2017) 243104.
[27]. Y. Kanai, Y. Ishibashi, T. Ono, K. Inoue, Y. Ohno, K. Maehashi, K. Matsumoto, Dynamical thermodiffusion model of graphene synthesis on polymer films by laser irradiation and application to strain sensors, Jpn. J. Appl. Phys., 56 (2017) 075102.
[28]. .Murata, K. Nozawa, N. Saitoh, N. Yoshizawa, T. Suemasu, K. Toko, 350 °C synthesis of high-quality multilayer graphene on an insulator using Ni-induced layer exchange, Appl. Phys. Lett., 13 (2020) 055502.
[29]. T. Tamura, K. Ueno, Low-temperature synthesis of multilayer graphene directly on SiO2 by current-enhanced solid-phase deposition using Ni catalyst, Jpn. J. Appl. Phys., 59 (2020) 066501.
[30]. Y. Bleu, F. Bourquard, A. S. Loir, V. Barnier, F. Garrelie, C. Donnet, Raman study of the substrate influence on graphene synthesis using a solid carbon source via rapid thermal annealing, J Raman Spectrosc., 2019.50: p. 1630–1641.
[31]. W. Xiong, Y. S. Zhou, L. J. Jiang, A. Sarkar, M. M. Samani, Z. Q. Xie, Y. Gao, N. J. Ianno, L. Jiang, Y. F. Lu, Single-Step Formation of Graphene on Dielectric Surfaces, Adv. Mater., 25 (2013) 630.
[32]. J. Torres, Y. Liu, S. So, H. Yi, S. Park, J. K. Lee, S. C. Lim, M. Yun, Effects of Surface Modifications to Single and Multilayer Graphene Temperature Coefficient of Resistance, ACS Appl. Mater. Interfaces., 12 (2020) 48890.
[33]. X. Y. Fanga, X. X. Yu, H. M. Zheng, H. B. Jin, L. Wang, M. S. Cao, Temperature- and thickness-dependent electrical conductivity of few-layer graphene and graphene nanosheets, Phys. Lett. A., 2015.379: p. 22452-251.
[34]. D. Chen, S. Chen, S. Yue, B. Lu, X. Pan, H. He, Z. Ye, N-ZnO nanorod arrays/p-GaN light-emitting diodes with graphene transparent electrode, J. Lumin., 216 (2019) 116719.
[35]. G. Jo, M. Choe, C. Y. Cho, J. H. Kim, W. Park, S. Lee, W. K. Hong, T. W. Kim, S. J. Park1, B. H. Hong, Y. H. Kahng, T. Lee, Large-scale patterned multi-layer graphene films as transparent conducting electrodes for GaN light-emitting diodes, Nanotechnology., 21 (2010) 175201.
[36]. Kun. Xu, C. Xu, J. Deng, Y. Zhu, W. Guo, M. Mao, L. Zheng, J. Sun, Graphene transparent electrodes grown by rapid chemical vapor deposition with ultrathin indium tin oxide contact layers for GaN light emitting diodes, Appl. Phys. Lett., 102 (2013) 162102.
[37]. M. A. Mastroa, O. M. Kryliouk, T. J. Anderson, A. Davydov, A. Shapiro, Influence of polarity on GaN thermal stability, J. Cryst. Growth., 274 (2005) 38.
[38]. J. Sun, M. T. Cole, S. A. Ahmad, O. Backe, T. Ive, M. Loffler, N. Lindvall, E. Olsson, K. B. K. Teo, J. Liu, A. Larsson, A. Yurgens, A. Haglund, Direct Chemical Vapor Deposition of Large-Area Carbon Thin Films on Gallium Nitride for Transparent Electrodes: A First Attempt, IEEE Trans. Semicond. Manuf., 25 (2012) 494.
[39]. J. Mischke, J. Pennings, E. Weisenseel, P. Kerger, M. Rohwerder, W. Mertin, G. Bacher, Direct growth of graphene on GaN via plasma-enhanced chemical vapor deposition under N2 atmosphere, 2D Mater., 7 (2020) 035019.