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GaN材料以其宽禁带、高击穿电场、高热导率、直接带隙等优势被广泛应用于光电子器件、大功率器件以及高频微波器件等方面. 由于GaN材料异质外延带来的大晶格失配和热失配问题, GaN在生长过程中会产生大量位错, 降低了GaN材料晶体质量, 导致器件性能难以进一步提升. 为此, 研究人员提出使用斜切衬底来降低位错密度, 但是关于斜切衬底上外延层的位错湮灭机制的研究还不充分. 所以, 本文采用金属有机化合物化学气相淀积技术在不同角度的斜切蓝宝石衬底上生长了GaN薄膜, 采用原子力显微镜、高分辨X射线衍射仪、光致发光测试、透射电子显微镜详细地分析了斜切衬底对GaN材料的影响. 斜切衬底可以显著降低GaN材料的位错密度, 但会导致其表面形貌发生退化. 并且衬底斜切角度越大, 样品的位错密度越低. 通过透射电子显微镜观察到了斜切衬底上特殊的位错终止现象, 这是斜切衬底降低位错密度的主要原因之一. 基于上述现象, 提出了斜切衬底上GaN生长模型, 解释了斜切衬底提高GaN晶体质量的原因.
GaN materials are widely used in optoelectronic devices, high-power devices and high-frequency microwave devices because of their excellent characteristics, such as wide frequency band, high breakdown electric field, high thermal conductivity, and direct band gap. Owing to the large lattice mismatch and thermal mismatch brought by the heterogeneous epitaxy of GaN material, the GaN epitaxial layer will produce a great many dislocations in the growth process, resulting in the poor crystal quality of GaN material and the difficulty in further improving the device performance. Therefore, researchers have proposed the use of vicinal substrate to reduce the dislocation density of GaN material, but the dislocation annihilation mechanism in GaN film on vicinal substrate has not been sufficiently studied. Therefore, in this paper, GaN thin films are grown on vicinal sapphire substrates at different angles by using metal organic chemical vapor deposition technique. Atomic force microscope, high resolution X-ray diffractometer, photoluminescence testing, and transmission electron microscopy are used to analyze in detail the effects of vicinal substrates on GaN materials. The use of vicinal substrates can significantly reduce the dislocation density of GaN materials, but lead to degradation of their surface morphology morphologies. And the larger the substrate vicinal angle, the lower the dislocation density of the sample is. The dislocation density of the sample with a 5º bevel cut on the substrate is reduced by about one-third compared to that of the sample with a flat substrate. The special dislocation termination on the mitered substrate is observed by transmission electron microscopy, which is one of the main reasons for the reducing the dislocation density on the mitered substrate. The step merging on the vicinal sapphire substrate surface leads to both transverse growth and longitudinal growth of GaN in the growth process. The transverse growth region blocks the dislocations, resulting in an abrupt interruption of the dislocations during propagation, which in turn reduces the dislocation density. Based on the above phenomena, a model of GaN growth on vicinal substrate is proposed to explain the reason why the quality of GaN crystal can be improved by vicinal substrate. -
Keywords:
- vicinal sapphire substrates /
- GaN /
- dislocation termination /
- transmission electron microscope
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图 1 四个样品的AFM测试图 (a) 样品A, RMS = 0.371 nm; (b) 样品B, RMS = 18.3 nm; (c) 样品C, RMS = 54.1 nm; (d) 样品D, RMS = 56.9 nm
Fig. 1. AFM images of four samples: (a) Sample A, RMS = 0.371 nm; (b) sample B, RMS = 18.3 nm; (c) sample C, RMS = 54.1 nm; (d) sample D, RMS = 56.9 nm.
图 2 样品A, B, C, D的(002)面(a)和(102)面(b)的XRD摇摆曲线图
Fig. 2. XRD rocking curves of (002) (a) and (102) (b) of samples A, B, C and D.
图 3 四个样品的室温下PL图(a)和局部放大图(b)
Fig. 3. PL images (a) and local enlarged images (b) of four samples at room temperature.
图 4 样品D的TEM测试图 (a) g = [0002]; (b)
$ g = $ $ [ {11\bar 2 0} ] $ Fig. 4. TEM images of sample D: (a) g = [0002]; (b)
$ g= $ $ [ {11\bar 2 0} ] $ .
图 5 斜切衬底上GaN的生长过程及位错传播过程
Fig. 5. Growth process and dislocation spread of GaN on vicinal substrates.
图 6 平面衬底上GaN的生长过程及位错传播过程
Fig. 6. Growth process and dislocation spread of GaN on planar substrates.
表 1 样品A, B, C, D的RC曲线FWHM值和位错密度
Table 1. FWHM values and dislocation density of RC curves of samples A, B, C and D.
样品 (002)面
FWHM值/('')(102)面
FWHM值/('')螺位错
密度/(107 cm–2)刃位错
密度/(108 cm–2)总位错
密度/(108 cm–2)Sample A 235 282 11.0 4.20 5.30 Sample B 221 274 9.76 3.97 4.94 Sample C 196 251 7.69 3.33 4.11 Sample D 165 240 5.47 3.07 3.62 
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[1] Morkoc H, Strite S, Gao G B, Lin M E, Sverdlov B, Burns M 1994 J. Appl. Phys. 76 1363
Google Scholar
[2] Kneissl M, Seong T Y, Han J, Amano H 2019 Nat. Photonics 13 233
Google Scholar
[3] 郭海君, 段宝兴, 袁嵩, 谢慎隆, 杨银堂 2017 66 167301
Google Scholar
Guo H J, Duan B X, Yuan S, Xie S L, Yang Y T 2017 Acta Phys. Sin. 66 167301
Google Scholar
[4] 武鹏, 张涛, 张进成, 郝跃 2022 71 158503
Google Scholar
Wu P, Zhang T, Zhang J C, Hao Y 2022 Acta Phys. Sin. 71 158503
Google Scholar
[5] Li G Q, Wang W L, Yang W J, Lin Y H, Wang H Y, Lin Z T, Zhou S Z 2016 Rep. Prog. Phys. 79 056501
Google Scholar
[6] Jena D, Mishra U K 2002 Appl. Phys. Lett. 80 64
Google Scholar
[7] 刘成, 李明, 文章, 顾钊源, 杨明超, 刘卫华, 韩传余, 张勇, 耿莉, 郝跃 2022 71 057301
Google Scholar
Liu C, Li M, Wen Z, Gu Z Y, Yang M C, Liu W H, Han C Y, Zhang Y, Geng L, Hao Y 2022 Acta Phys. Sin. 71 057301
Google Scholar
[8] Zhou S J, Zhao X Y, Du P, Zhang Z Q, Liu X, Liu S, Guo A 2022 Nanoscale 14 4887
Google Scholar
[9] Kung P, Walker D, Hamilton N, Diaz J, Razeghi M 1999 Appl. Phys. Lett. 74 570
Google Scholar
[10] Zhao Y, Xu S R, Feng L S, Peng R S, Fan X M, Du J J, Su H K, Zhang J C, Hao Y 2022 Mater. Sci. Semicond. Process. 143 106535
Google Scholar
[11] Ni Y Q, He Z Y, Zhou D Q, Yao Y, Yang F, Zhou G L, Shen Z, Zhong J, Zhen Y, Zhang B J, Liu Y 2015 Superlattices Microstruct. 83 811
Google Scholar
[12] Fatemi M, Wickenden A E, Koleske D D, Twigg M E, Freitas J A, Henry R L, Gorman R J 1998 Appl. Phys. Lett. 73 608
Google Scholar
[13] Shen X Q, Shimizu M, Okumura H 2003 Jpn. J. Appl. Phys. 42 L1293
Google Scholar
[14] Chang P C, Yu C L 2008 J. Electrochem. Soc. 155 H369
Google Scholar
[15] Zhang H C, Sun Y, Song K, et al. 2022 Appl. Phys. Lett. 119 072104
Google Scholar
[16] Fan X M, Bai J C, Xu S R, Zhang J C, Li P X, Peng R S, Zhao Y, Du J J, Shi X F, Hao Y 2018 Thin Solid Films 663 44
Google Scholar
[17] Shen X Q, Matsuhata H, Okumura H 2005 Appl. Phys. Lett. 86 021912
Google Scholar
[18] 林志宇, 张进成, 许晟瑞, 吕玲, 刘子扬, 马俊彩, 薛晓咏, 薛军帅, 郝跃 2012 61 186103
Google Scholar
Lin Z Y, Zhang J C, Xu S R, Lü L, Liu Z Y, Ma J C, Xue X Y, Xue J S, Hao Y 2012 Acta Phys. Sin. 61 186103
Google Scholar
[19] Chuang R W, Yu C L, Chang S J, Chang P C, Lin J C, Kuan T M 2007 J. Cryst. Growth 308 252
Google Scholar
[20] Xu Z H, Zhang J C, Zhang Z F, Zhu Q W, Duan H T, Hao Y 2009 Chin. Phys. B 18 5457
Google Scholar
[21] Sun H D, Mitra S, Subedi R C, et al. 2019 Adv. Funct. Mater. 29 1905445
Google Scholar
[22] Zhang H C, Sun Y, Song K, Xing C, Yang L, Wang D H, Yu H B, Xiang X Q, Gao N, Xu G W, Sun H D, Long S B 2021 Appl. Phys. Lett. 119 072104
Google Scholar
[23] Shen X Q, Furuta K, Nakamura N, Matsuhata H, Shimizu M, Okumura H 2007 J. Cryst. Growth 301 404
Google Scholar
[24] Chierchia R, Bottcher T, Heinke H, Einfeldt S, Figge S, Hommel D 2003 J. Appl. Phys. 93 8918
Google Scholar
[25] 郝跃, 张金风, 张进成 2013 氮化物宽禁带半导体材料与电子器件(北京: 科学出版社) 第25页
Hao Y, Zhang J F, Zhang J C 2013 Nitride Wide Bandgap Semiconductor Materials and Electronic Devices (Beijing: Science Press) p25
[26] Xu S R, Hao Y, Zhang J C, Jiang T, Yang L A, Lu X L, Lin Z Y 2013 Nano Lett. 13 3654
Google Scholar
[27] Yu H B, Chen H, Li D S, Wang J, Xing Z G, Zheng X H, Huang Q, Zhou J M 2004 J. Cryst. Growth 266 455
Google Scholar
[28] Lee J H, Lee D Y, Oh B W, Lee J H 2010 IEEE Trans. Electron Devices 57 157
Google Scholar
[29] Kong B H, Sun Q, Han J, Lee I H, Cho H K 2012 Appl. Surf. Sci. 258 2522
Google Scholar
[30] Pakula K, Baranowski J M, Borysiuk J 2007 Cryst. Res. Technol. 42 1176
Google Scholar
[31] Tao H C, Xu S R, Zhang J C, Su H K, Gao Y, Zhang Y C, Zhou H, Hao Y 2023 Opt. Express 31 20850
Google Scholar
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