本論文以雙電子槍蒸鍍系統製備p-GaN的藍光反射式歐姆電極AgPt(6 at%)、AgPt(4 at%)、AgPt(2 at%)、Pt(2 nm)/Ag(150 nm)、AgRh(2 at%)及AgRu(2 at%)等六組試片，探討不同合金成分以及爐管退火(FA)與快速退火(RTA)兩種退火方式對於藍光反射式歐姆電極光電特性與熱穩定性的影響。探討內容包含歐姆電極的藍光反射率、金屬薄膜片電阻與特徵接觸電阻，以及各性質之熱穩定性。並使用掃描式電子顯微鏡觀察試片表面樣貌，分析不同合金成分的特性差異及抑制退火後Ag薄膜凝聚(agglomeration)的效果。我們發現AgPt(2 at%)、Pt(2 nm)/Ag(150 nm)皆無法抑制Ag的凝縮，AgPt(4 at%)及AgPt(6 at%)能抑制薄膜的高溫退火凝聚。而AgRh(2 at%)與AgRu(2 at%)合金薄膜經500 ℃退火後表面未發現明顯破孔；但AgRu(2 at%)經爐管退火再於400 ℃時效1小時後有些許破孔產生，因此造成反射率下降。其他試片經爐管退火或快速退火，且經400 ℃時效退火1小時後反射率變化不大。六組試片的金屬薄膜片電阻都小於1 Ω/□，且具熱穩定性。在特徵接觸電阻上，AgPt合金於退火後的特徵接觸電阻會隨著Pt成份的增加而下降，但在Pt添加的量大於4 at%時，AgPt再經時效時Ag會產生側向擴散，引發電極漏電現象；而AgRh(2 at%)與AgRu(2 at%)的特徵接觸電阻數值皆具良好熱穩定性。整體來說，AgRu(2 at%)表現最佳，經大氣環境500 ℃快速退火1分鐘後，可以於460 nm藍光具93%的光反射率，金屬薄膜片電阻約為0.2Ω/□，特徵接觸電阻約為7.4× 10-4 Ω-cm2且具良好熱穩定性。另外也可以看出在Ag與少量貴金屬(Pt, Ru, Rh)形成合金時，貴金屬元素本身功函數的大小不是影響特徵接觸電阻值大小的主要原因。

In this study, all the samples AgPt(6 at%), AgPt(4 at%), AgPt(2 at%), Pt(2 nm)/Ag(150 nm), AgRh(2 at%) and AgRu(2 at%) were deposited on the p-GaN by dual E-gun evaporation system. The samples were annealed at 500℃ by two different annealing conditions, furnace annealing(FA) in air ambient for 10 min, and rapid thermal annealing(RTA) in air ambient for 1 min. Thermal stability test were performed by annealing at 400℃in air ambient for 60 min. Optoelectricproperties and thermal stability of p-GaN/AgPt, p-GaN/AgRu and p-GaN/AgRh reflective ohmic contacts were investigated by SEM analysis, reflectance at 460 nm, sheet resistance of metal film , and specific contact resistance.The result show annealed AgPt(6 at%), AgPt(4 at%),AgRh(2 at%) and AgRu(2 at%) could suppress the agglomeration of Ag film.In AgPt(6 at%) and AgPt(4 at%),Ag would produce lateral diffusion causing electrode leakage phenomenon when aging at 400 ℃ for one hour. Comprehensive consideration above-mentioned properties,AgRu (2 at%) alloys thin films are excellent.After anneal 1min in air at 500 ℃, the AgRu(2 at%) reflectors produce low specific contact resistance(7.4 × 10-4 Ω-cm2), high reflectivity(93% at 460nm),good sheet resistance of the metal thin film(0.2 Ω/□), and good thermal stability. Otherwise, we could also find that the work function of the magnitude of the noble metal element itself could't be the main cause of the magnitude of the specific contact resistance ,when small amount of Ag and a noble metal (Pt, Ru, Rh) alloy is formed.

1.H. Amano, N. Sawaki, I. Akasaki and Y. Toyoda, “Metalorganic vapor phase epitaxial growth of a high quality GaN film using an AlN buffer layer,” Appl. Phys. Lett. 48, 353 (1986).
2.H. Amano, M. Kito, K. Hiramatsu, and I. Akasaki, “P-type conduction in Mg-doped GaN treated with low-energy electron beam irradiation (LEEBI),” Jpn. J. Appl. Phys. 28 , L2112 (1989).
3.S. Nakamura, M. Senoh, and T. Mukai, “Highly p-typed Mg-doped GaN films grown with GaN buffer layers,” Jpn. J. Appl. Phys. 30 , L1708 (1991).
4.S. Nakamura, “GaN growth using GaN buffer layer,” Jpn. J. Appl. Phys. 30, L1705 (1991).
5.陳延存，國立清華大學材料與工程學系碩士學位論文, (2010)。
6.A. Y. C. Yu, “Electron tunneling and contact resistance of metal-silicon contact barriers,” Solid State Electron. 13, 239 (1970).
7.C. Y. Chang, Y. K. Fang, and S. M. Sze, “Specific contact resistance of metal-semiconductor barriers,” Solid State Electron. 14, 541 (1971).
8.S. M. Sze, Physics of Semiconductor Devices (Wiley, New York), p.245, 1981.
9.J. T. Trexler, S. J. Pearton, P. H. Holloway, M. G. Mier, K. R. Evans, and R. F. Karlicek, “Comparison of Ni/Au, Pd/Au, and Cr/Au Metallizations for Ohmic Contacts to p-GaN,” Mater. Res. Soc. Symp. Proc. 449, 1091 (1997).
10.F. A. Padovani, and R. Stratton, “Field and thermionic-field emission in Schottky barriers,” Solid State Electron. 9, 695 (1966).
11.C. R. Crowell, and V. L. Rideout, “Normalized thermionic-field (TF) emission in metal-semiconductor (Schottky) barriers,” Solid State Electron. 12, 89 (1969).
12.R. Stratton, and F. A. Padovani, “Differential resistance peaks of Schottky barrier diodes,” Solid State Electron. 10, 813 (1967).
13.G. S. Marlow, and M. B. Das, “The Effects of Contact Size and Non-Zero Metal Resistance on the Determination of Specific Contact Resistance,” Solid State Electron. 25, 91 (1982).
14.V. Y. Niskov, and G. A. Kubetskii, “Resistance of ohmic contacts between metals and semiconductor films,” Sov. Phys. Semicond. 4, 1553 (1971).
 
15.W. G. Bickley, Bessel Functions, pp. 220-225. University Press, Cambridge (1960).
16.J. J. Wierer, D. A. Steigerwald, M. R. Krames, J. J. O’Shea, M. J. Ludowise,G.Christenson, Y.C. Shen, C. Lowery, P. S. Martin, S. Subramanya, W. Götz,N. F. Gardner, R. S. Kern, and S. A. Stockmam, “High-power AlGaInN flip-chip light-emitting diodes,” Appl. Phys. Lett. 78, 3379 (2001).
17.W. S. Chen, S. C. Shei, S. J. Chang, Y. K. Su, W. C. Lai, C. H. Kuo, Y. C. Lin, C. S. Chang, T. K. Ko, Y. P. Hsu, and C. F. Shen, “Rapid thermal annealed InGaN/GaN flip-chip LEDs,” IEEE Trans. Electron Devices. 53, 32 (2006).
18.S. J. Cai, R. Li, Y. L. Chen, L. Wong, W. G. Wu, S. G. Thomas, and K. L. Wang, “High performance AlGaN/GaN HEMT with improved ohmic contacts,” Elctron. Lett. 34, 2354 (1998).
19.Z. Fan, S. N. Mohammad, W. Kim, O. Aktas, A. E. Botchkarev, and H. Morkoc, “Very low resistance multilayer Ohmic contact to n-GaN,” Appl. Phys. Lett. 68, 1672 (1996).
20.J. K. Kim, J. L. Lee, J. W. Lee, H. E. Shin, Y. J. Park, and T. Kim, “Low resistance Pd/Au ohmic contacts to p-type GaN using surface treatment,” Appl. Phys. Lett. 73, 2953 (1998).
21.J. Sun, K. A. Rickert, J. M. Redwing, A. B. Ellis, F. J. Himpsel, and T. F. Kuech, “p-GaN surface treatments for metal contacts,” Appl. Phys. Lett. 76, 415 (2000).
22.H. Ishikawa, S. Kobayashi, Y. Koide, S. Yamasaki, S. Nagai, J. Umezaki, M. Koike, and M. Murakami, “Effects of surface treatments and metal work functions on electrical properties at p-GaN/metal interfaces,” J. Appl. Phys. 81, 1315 (1997).
23.S. Nakamura, N. Iwasa, M. Senoh, and T. Mukai, “Hole Compensation Mechanism of P-Type GaN Films,” Jpn. J. Appl. Phys. 31, 1258 (1992).
24.Y. Ohba, and A. Hatano, “H-atom incorporation in Mg-doped GaN grown by metalorganic chemical vapor deposition,” Jpn. J. Appl. Phys. 33, L1367 (1994)
25.Y. J. Lin, “H-atom incorporation in Mg-doped GaN grown by metalorganic chemical vapor deposition,” Appl. Phys. Lett. 84,2760 (2004)
26.I. Wakia, H. Fujioka, M. Oshima, H. Miki, M. Okuyama, “Low-temperature activation of Mg-doped GaN with thin Co and Pt films,” Appl. Surf. Sci. 190, 339 (2002).
27.T. Wei, J. Wang, N. Liu, H. Lu, Y. Zeng, G. Wang, and J. Li, “Catalytic Activation of Mg-Doped GaN by Hydrogen Desorption Using Different Metal Thin Layers,” Jpn. J. Appl. Phys. 49, 100201 (2010).
28.李正中，薄膜光學與鍍膜技術，藝軒圖書出版社，2002年，P.144
29.J. O. Song, J. S. Kwak, Y. Park, and T. Y. Seong, “Ohmic and degradation mechanisms of Ag contacts on p-type GaN,” Appl. Phys. Lett. 86, 062104 (2005).
30.J. Y. Kim, S. I. Na, G. Y. Ha, M. K. Kwon, I. K. Park, J. H. Lim, and S. J. Park, “Thermally stable and highly reflective AgAl alloy for enhancing light extraction efficiency in GaN light-emitting diodes,” Appl. Phys. Lett. 88, 043507 (2006).
31.S. K. Sharma, and J. Spitz, “Hillock formation hole growth and agglomeration in thin silver films,” J. Appl. Phys. 86, 4491 (1999).
32.D. S. Zhao, S. M. Zhang, L. H. Duan, Y. T. Wang, D. S. Jiang, W. B. Liu, B. S. Zhang, and H. Yang, “Effects of Ag on Electrical Properties of Ag/Ni/p-GaN Ohmic Contact,” Phys. Lett. 24, 1741 (2007).
33.H. W. Jang, and J. L. Lee, “Mechanism for ohmic contact formation of Ni/Ag contacts on p-type GaN,” Appl. Phys. Lett. 85, 5920 (2004).
34.D. S. Leem, J. O. Song, H. G. Hong, J. S. Kwak, Y. Park, and T. Y. Seong, “High-Quality Cu-Ni Solid Solution/Ag Ohmic Contacts for Flip-Chip Light-Emitting Diodes,” Phys. Stat. Sol. (a). 201, 2823 (2004)
35.J. O. Song, D. S. Leem, J. S. Kwak, O. H. Nam, Y. Park, and T. Y. Seong, “Low-resistance and highly-reflective Zn–Ni solid solution/Ag ohmic contacts for flipchip light-emitting diodes,” Appl. Phys. Lett. 83, 4990 (2003)
36.K. Y. Ban, H. G. Hong, D. Y. Noh, J. I. Sohn, D. J. Kang, and T. Y. Seong, “Ir/Ag reflector for high-performance GaN-based near UV light emitting diodes,” Mater. Sci. Eng. B. 133, 26 (2006)
37.J. Cho, H. Kim, Y. Park, and E. Yoon, “Effects of p-electrode reflectivity on extraction efficiency of nitride-based light-emitting diodes,” Appl. Phys. Expr. 1, 052001 (2008).
38.K. Y. Ban, H. G. Hong, D. Y. Noh, T. Y. Seong, J. O. Song, and D. Kim, “Use of an indium zinc oxide interlayer for forming Ag-based Ohmic contacts to p-type GaN for UV-light-emitting diodes,” Semicond. Sci. Technol. 20, 921 (2005).
39.J. O. Song, J. S. Kwak, and T. Y. Seong, “Cu-doped indium oxide/Ag ohmic contacts for high-power flip-chip light-emitting diodes,” Appl. Phys. Lett. 86, 062103 (2005).
40.H. G. Hong, K. Y. Ban, J. O. Song, J. Cho, Y. Park, J. S. Kwak, I. T. Ferguon, and T. Y. Seong, “High quality tin zinc oxide/Ag ohmic contacts for UV flip-chip light-emitting diodes,” Phys. Stat. Sol. (c)3, 2133 (2006).
41.J. O. Song, D. S. Leem, J. S. Kwak, O. H. Nam, Y. Park, and T. Y. Seong. Low resistance and reflective, “Mg-doped indium oxide-Ag ohmic contacts for flip-chip light-emitting diodes,” IEEE Phot. Tech. Lett. 16, 1450 (2004)
42.H. G. Hong, J. O. Song, T. Lee, I. T. Ferguson, J. S. Kwak, and T. Y. Seong, “Improvement of the reverse leakage behavior of Ag-based ohmic contacts for GaN-based light-emitting diodes using MgZnO interlayer,” Mater. Sci. Eng. B. 129, 176 (2006).
43.H. W. Jang, and J. L. Lee, “Low-resistance and high-reflectance Ni Ag Ru Ni Au ohmic contact on p -type GaN,” Appl. Phys. Lett. 85, 4421 (2004).
44.J. H. Son, G. H. Jung, and J. L. Lee, “Enhancement of light reflectance and thermal stability in Ag–Cu alloy contacts on p -type GaN,” Appl. Phys. Lett. 93, 012102 (2008).
45.H. Kim, K. H. Baik, J. Cho, J. W. Lee, S. Yoon, H Kim, S. N Lee, C. Sone, Y. Park, and T. Y. Seong, “High-reflectance and thermally stable AgCu alloy p-type reflectors for GaN-based light-emitting diodes,” IEEE Phot. Tech. Lett. 19, 336 (2007).
46.J. H. Son, G. H. Jung, and J. L. Lee, “Highly reflective Ag–Cu alloy-based ohmic contact on p-type GaN using Ru overlayer,” Opt. Lett. 33, 2907 (2008).
47.R. Kawai, T. Mori, W. Ochiai, A. Suzuki, M Iwaya, H. Amano, S. Kamiyama, and I. Akasaki, “High-reflectivity Ag-based p-type ohmic contacts for blue light-emitting diodes,” Phys. Status Solidi C. 6, S830 (2009).
48.G. H. Jung, J. H. Son, Y. H. Song, and J. L. Lee, “Strain induced suppression of silver agglomeration of indium-containing silver contact,” Appl. Phys. Lett. 96, 201904 (2010).
49.Y. H. Song, J. H. Son, G. H. Jung, and J. L. Lee, “Effects of Mg Additive on Inhibition of Ag Agglomeration in Ag-Based Ohmic Contacts on p-GaN,” Electrochm. Solid-State Lett. 13, H173 (2010)
50.B. Y. Cheng, I. C. Chen, C. H. Kuo, and L. C. Chang, “High Reflectance Contacts to P-type GaN Using Ag-La Alloys,” ECS Transactions. 44, 1285 (2012).
51.J. Y. Kim, S. I. Na, G. Y. Ha, M. K. Kwon, I. K. Park, J. H. Lim, and S. J. Park, “Thermally stable and highly reflective AgAl alloy for enhancing light extraction efficiency in GaN light-emitting diodes,” Appl. Phys. Lett. 88, 043507 (2006).
52.S. M. Sze, Semiconductor devices, physics and technology (Wiley ; Bell Telephone Lab, New York), p.37, 1985.