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硅衬底GaN基发光二极管（LED）的内置n型欧姆接触在晶圆键合时的高温过程中常常退化，严重影响LED的工作电压等器件性能.本文深入研究了内置n电极蒸镀前对n-GaN表面的等离子体处理工艺对硅衬底GaN基发光二极管n型欧姆接触特性的影响.实验结果表明，1.1 mm1.1 mm的LED芯片在350 mA电流下，n-GaN表面未做等离子体处理时，n电极为高反射率Cr/Al的芯片正向电压为3.43 V，比n电极为Cr的芯片正向电压高0.28 V.n-GaN表面经O2等离子体表面处理后，Cr/Al和Cr电极芯片的正向电压均有所降低，但Cr/Al电极芯片的正向电压仍比Cr电极芯片高0.14 V.n-GaN表面经Ar等离子体处理后，Cr/Al电极芯片正向电压降至Cr电极芯片的正向电压，均为2.92 V.利用X射线光电子能谱对Ar等离子体处理前后的n-GaN表面进行分析发现，Ar等离子体处理增加了n-GaN表面的N空位（施主）浓度，更多的N空位可以提高n型欧姆接触的热稳定性，缓解晶圆键合的高温过程对n型欧姆接触特性的破坏.同时还发现，经过Ar等离子体处理并用HCl清洗后，n-GaN表面的O原子含量略有增加，但其存在形式由以介电材料GaOx为主转变为导电材料GaOxN1-x和介电材料GaOx含量相当的状态，这会使得接触电阻进一步降低.上述两方面的变化均有利于降低LED芯片的正向电压.Unlike the finger-like n-contact that is prepared after the wafer bonding and the N-polar GaN surface roughening for GaN-based vertical structure light-emitting diodes (LEDs) grown on Si substrates, the embedded via-like n-contact is formed prior to the wafer bonding. The high temperature process of the wafer bonding often causes the electrical characteristics of the via-like embedded n-contact to degrade. In this paper, we study in detail the effect of plasma treatment of the n-GaN surface on the forward voltage of GaN-based LED grown on Si substrate. It is shown that with no plasma treatment on the n-GaN surface, the forward voltage (at 350 mA) of the 1.1 mm1.1 mm chip with a highly reflective electrode of Cr (1.1 nm)/Al is 3.43 V, which is 0.28 V higher than that of the chip with a pure Cr-based electrode. The LED forward voltages for both kinds of n-contacts can be reduced by an O2 plasma treatment on the n-GaN surface. But the LED forward voltage with a Cr/Al-based electrode is still 0.14 V higher than that of the chips with a pure Cr-based electrode. However, after an Ar plasma treatment on the n-GaN surface, the LED forward voltage with a Cr/Al-based electrode is reduced to 2.92 V, which is equal to that of the chip with a pure Cr-based electrode. The process window of the n-GaN surface after the Ar plasma treatment is broader. X-ray photoelectron spectroscopy is used to help elucidate the mechanism. It is found that Ar plasma treatment can increase the concentration of N-vacancies (VN) at the n-GaN surface. VN acts as donors, and higher VN helps improve the thermal stability of n-contact because it alleviates the degradation of the n-contact characteristics caused by the high temperature wafer bonding process. It is also found that the O content increases slightly after the Ar plasma treatment and HCl cleaning. The O atoms are mainly present in the dielectric GaOx film before the Ar plasma treatment and the HCl cleaning, and they exist almost equivalently in the conductive GaOxN1-x film and the dielectric GaOx film after Ar treatment and HCl cleaning. The conductive GaOxN1-x film and the VN donors formed during the plasma treatment can reduce the contact resistance and the LED forward voltage.
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Keywords:
- GaN /
- light-emitting diode /
- plasma surface treatment /
- n-contact
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[1] Nakamura S, Senoh M, Mukai T 1993 Jpn. J. Appl. Phys 32 L8
[2] Narukawa Y, Ichikawa M, Sanga D, Sano M, Mukai T 2010 J. Phys. D:Appl. Phys. 43 354002
[3] Haerle V, Hahn B, Kaiser S, Weimar A, Bader S, Eberhard F, Plssl A, Eisert D 2004 Phys. Status Solidi(a) 201 2736
[4] Fujii T, Gao Y, Sharma R, Hu E L, Denbaars S P, Nakamura S 2004 Appl. Phys. Lett. 84 855
[5] Chu C F, Cheng C C, Liu W H, Chu J Y, Fan F H, Cheng H C, Doan T, Tran C A 2010 P. IEEE 98 1197
[6] Jeong H H, Sang Y L, Jeong Y K, Choi K K, Song J O, Lee Y H, Seong T Y 2010 Electrochem. Solid-State Lett. 13 H237
[7] Lee S Y, Choi K K, Jeong H H, Kim E J, Son H K, Son S J, Song J O, Seong T Y 2011 Jpn. J. Appl. Phys. 50 2005
[8] Laubsch A, Sabathil M, Baur J, Peter M, Hahn B 2010 IEEE Trans. Electron Dev. 57 79
[9] Hahn B, Galler B, Engl K 2014 Jpn. J. Appl. Phys. 53 100208
[10] Han J, Le D, Jin B, Jeong H, Song J O, Seong T Y 2015 Mat. Sci. Semicon. Pro. 31 153
[11] Greco G, Iucolano F, Roccaforte F 2016 Appl. Surf. Sci. 383 324
[12] Song J O, Kwak J S, ParkY J, Seong T Y 2005 Appl. Phys. Lett. 86 062104
[13] Son J H, Song Y H, Yu H K, Lee J L 2009 Appl. Phys. Lett. 35 062108
[14] Leung B, Han J, Sun Q 2014 Phys. Status Solidi (c) 11 437
[15] Sun Q, Yan W, Feng M X, Li Z C, Feng B, Zhao H M, Yang H 2016 J. Semicond. 32 044006
[16] Sun Y, Zhou K, Sun Q, Liu J P, Feng M X, Li Z C, Zhou Y, Zhang L Q, Li D Y, Zhang S M, Ikeda M, Liu S, Yang H 2016 Nature Photon. 158 1
[17] Luther B P, Mohney S E, Jackson T N, Khan M A, Chen Q, Yang J W 1997 Appl. Phys. Lett. 70 57
[18] Kim H, Park N M, Jang J S, Park S J, Hwang H 2001 Electrochem. Solid-State Lett. 4 G104
[19] Kim H, Ryou J H, Dupuis R D, Lee S N, Park Y, Jeon J W, Seong T Y 2008 Appl. Phys. Lett. 93 192106
[20] Liu J, Feng F, Zhou Y, Zhang J, Jiang F 2011 Appl. Phys. Lett. 99 111112
[21] Kim S J, Nam T Y, Kim T G 2011 IEEE Electr. Device L. 32 149
[22] Jeong T, Kim S W, Lee S H, Ju J W, Lee S J, Baek J H, Lee J K 2011 J. Electrochem. Soc. 158 H908
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