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GaN基发光二极管(LED)中的残余应力状态对器件的性能和稳定性有很大影响. 通过使用三种不同的键合衬底(Al2O3衬底, CuW衬底和Si衬底)以及改变键合温度(290 ℃, 320 ℃, 350 ℃和380 ℃), 并且使用不同的激光能量密度(875, 945和1015 mJ·cm-2) 进行激光剥离, 制备了不同应力状态的GaN基LED器件. 对不同条件下GaN LED进行弯曲度、Raman 散射谱测试. 实验结果表明, 垂直结构LED中的残余应力的状态是键合衬底和键合金属共同作用的结果, 而键合温度影响着垂直结构LED中的残余应力的大小. 激光剥离过程中, 一定能量密度下激光剥离工艺一般不会对芯片中的残余应力造成影响, 但是如果该工艺对GaN 层造成了微裂缝, 则会在一定程度上起到释放残余应力的作用. 使用Si衬底键合后, 外延蓝宝石衬底翘曲变大, 对应制备的GaN基垂直结构 LED中的残余应力为张应力, 并且随着键合温度的上升而变大; 而Al2O3和CuW衬底制备的LED中的残余应力为压应力, 但使用Al2O3衬底键合制备的LED中压应力随键合温度上升而一定程度变大, CuW 衬底制备的LED中压应力随键合温度上升而下降.Residual stress conditions in GaN-based LEDs will have a significant influence on device performance and reliability. In this paper, GaN-based vertical LEDs under different stress conditions are fabricated by bonding with three types of submounts (Al2O3 submount, CuW submount and Si submount), changing the soak temperature (290 ℃, 320 ℃, 350 ℃ and 380 ℃) and using different laser energy densities (875, 945 and 1015 mJ·cm-2). The warpage and Raman scattering spectra of those GaN-based LEDs are measured. The experimental results show that the residual stress conditions in GaN-based vertical LEDs are a consequence of the bonded submounts and bonded metal, and the soak temperature is the primary factor that determines the degree of residual stress in LED chips. In the laser lift-off process, changing laser energy density in an appropriate range has little influence on residual strain of LED chips, and the micro-cracks in GaN layer caused by LLO process will play a role in releasing the residual stress. The warpage of epitaxial sapphire substrate becomes large after boding with Si submount, the residual stress in GaN-based vertical LEDs is tensile stress and becomes larger with the soak temperature rising. When GaN epi wafer bonds with Al2O3 submount and CuW submount, the warpages becomes small and large respectively and the residual stress in chips is compressive stress. Because of the mismatch of coefficient of thermal expansion, the compressive stress in GaN-based LED chips increases for Al2O3 submount and drops for CuW submount with the soak temperature rising.
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Keywords:
- residual stress /
- vertical light emitting diodes /
- wafer bonding /
- laser lift-off
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[1] Nakamura S, Senoh M, Iwasa N 1996 Jpn. J. Appl. Phys. 35 217
[2] Nakamura S, Senoh M, Nagahama S 1998 Jpn. J. Appl. Phys. 37 1020
[3] Kang T S, Wang X T, Lo C F 2012 J. Vac. Sci. Technol. B 30 011203
[4] Zhang B, Egawa T, Ishikawa H 2003 Jpn. J. Appl. Phys. 42 L226
[5] Ng W N, Leung C H, Lai P T 2008 Nanotechnology 19 255302
[6] Yang Y, Lin Y, Xiang P 2014 Appl. Phy. Express 7 042102
[7] Wu K, Wei T B, Lan D 2014 Chin. Phys. B 23 028504
[8] Chen W C, Tang H L, Luo P 2014 Acta Phys. Sin. 63 068103 (in Chinese) [陈伟超, 唐慧丽, 罗平 2014 物理学报 63 068103]
[9] Li J Z, Tao Y B, Chen Z Z, Jiang X Z 2014 Chin. Phys. B 23 016101
[10] Barghout K, Chaudhuri J 2004 J. Mater. Sci. 39 5817
[11] Yuseong J, Won Rae K, Dong-Hyun J 2010 J. Appl. Phys. 107 113537
[12] Tan B S, Yuan S, Kang X J 2004 Appl. Phys. Lett. 84 2757
[13] Chu C F, Lai F I, Chu J T 2004 J. Appl. Phys. 95 3916
[14] Yongjian S, Tongjun Y, Chuanyu J 2010 Chin. Phys. Lett. 27 127303
[15] Chen M, Zhang J Y, L X Q, Ying L Y 2013 Chin. Phys. Lett. 30 014203
[16] Tetsuzo U, Masahiro I, Masaaki Y 2011 Jpn. J. Appl. Phys. Lett. 50 041001
[17] Hsu S C, Pong B J, Li W H 2007 Appl. Phys. Lett. 91 251114
[18] Zhao D G, Xu S J, Xie M H 2003 Appl. Phys. Lett. 83 677
[19] Xiong C B, Jiang F Y, Fang W Q 2008 Acta Phys. Sin. 57 3176 (in Chinese) [熊传兵, 江风益, 方文卿 2008 物理学报 57 3176]
[20] Kim S 2011 J. Electrochem. Soc. 158 904
[21] Huang Y P, Yun F, Ding W 2014 Acta Phys. Sin. 63 127302 (in Chinese) [黄亚平, 云峰, 丁文 2014 物理学报 63 127302]
[22] Zhang L, Shao Y L, Hao X 2011 J. Cryst. Growth 334 62
[23] Lin B W, Wu N J, Wu Y C S 2013 J. Display Technol. 9 371
[24] Jinsub P, Takenari G, Takafumi Y, Seogwoo L 2013 J. Phys. D: Appl. Phys. 46 155104
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