氮化鎵的寬能隙、低導通電阻、高電流密度以及高崩潰電壓的材料特性使之在功率元件的應用上相較於矽材料有相當大的優勢，而在近幾年來，建立於矽基板上之氮化鋁鎵/氮化鎵高電子遷移率電晶體(AlGaN/GaN HEMT)已被廣泛研究與討論，其中，因緩衝層的品質好壞而造成的漏電流更為此領域的重要議題之一。對於功率元件的應用而言，過大之漏電流容易造成能源的浪費且將會嚴重降低系統運轉的效率。這之間已有研究指出元件的歐姆接觸製程為造成緩衝層漏電流的原因之一，故近年來，有研究提出使用蕭特基汲極技術可以使氮化鋁鎵/氮化鎵高電子遷移率電晶體擁有較低漏電流且較高崩潰電壓的特性。然而，蕭特基汲極特有之蕭特基導通電壓卻會造成元件導通電阻的增加，這一樣會造成系統運轉的效率變差。在本研究中，我們製作了建立於矽基板上之蕭特基-歐姆混合汲極結構之AlGaN/GaN HEMTs，其能同時改善典型HEMT元件在開啟和關閉狀態時的直流特性。在不增加任何光罩或改變製程步驟的條件下就可以達到降低漏電流、導通電阻以及提高崩潰電壓之目的。由量測結果顯示使用該結構能有效消除蕭特基汲極之導通電壓，且較原典型結構之元件與蕭特基汲極元件增加10%的飽和電流。對於元件在關閉時的特性，使用該結構更有效降低原典型元件兩個數量級之漏電流，且同時擁有較高的崩潰電壓。

[1] S. M. Sze, Physics of Semiconductor Devices, 2nd ed., Wiley, New York, 1981.
[2] B. Gelmont, K. Kim, and M. Shur, “Monte Carlo Simulation of Electron Transport in Gallium Nitride,” J. Appl. Phys., 74(3), pp. 1818-1821, 1993.
[3] O. Ambacher, “Growth and applications of group III-nitrides,” Journal of Physics D (Applied Physics), vol. 31, pp.2653-2710, 1998.
[4] B. J. Baliga, “Power Semiconductors Devices,” Boston:PWS pp. 28-29, 1996
[5] 張育榮, “場效電板氮化鋁鎵/氮化鎵高電子移導率電晶體之製作與應用,” 2006 中央大學電機所碩士班論文.
[6] J. L. Hudgins, G. S. Simin, E.Santi and M.A. Khan, “An Assessment of Wide Bandgap Semiconductors for Power Devices,” IEEE trans. On power electronics, 18(3), pp. 907-914, 2003.
[7] O. Ambacher et al., “Two-dimension electron gases induced byspontaneous and piezoelectric polarization charges in N- and Ga-face AlGaN/GaN heterostructures,” Journal of Applied Physics, vol 85, Num 6, (3222), 1999.
[8] B. J. Baliga, “Semiconductors for high-voltage vertical channel FETs,” J. Appl. Phys., vol. 53, pp. 1759-64, 1982.
[9] J. P. Ibbetson, P. T. Fini, K. D. Ness, S. P. DenBars, J. S. Speck, and U. K. Mishra, “Polarization effects, surface states, and the source of electronics in AlGaN/GaN heterostructure field effect transistors,” Applied Physics Letters, vol. 77, pp. 250-2, 2000.
[10] C. L. Chen, “Breakdown of Overlapping-Gate GaAs MESFETs,” IEEE Transactions on Electron Devices, 43(4), pp. 535-542, 1996.
[11] S. Karmalkar and U. K. Mishra, “Enhancement of Breakdown Voltage in AlGaN/GaN High Electron Mobility Transistors Using a Field Plate,” IEEE Transactions on Electron Devices, 48(8), pp. 1515-1521, 2001.
[12] S. Arulkumaran et al., “Enhancement of breakdown voltage by AlN buffer layer thickness in AlGaN/GaN high-electron-mobility transistors on 4 in. diameter silicon,” Appl. Phys. Lett., 85(2005) 123503-1.
[13] Y. C. Choi et al., “The Effect of an Fe-doped GaN Buffer on OFF-State Breakdown Characteristics in AlGaN/GaN HEMTs on Si Substrate,” IEEE Trans. Electron Devices, 53(2006) 2926.
[14] B. Lu et al., “Schottky-Drain Technology for AlGaN/GaN High-Electron Mobility Transistors,” IEEE Electron Device Lett., 31(2010) 302.
[15] Y. Dora, A. Chakraborty, S. Heikman, L. McCarthy, S. Keller, S. P. DenBaars, U. K. Mishra, “Effect of Ohmic Contacts on Buffer Leakage of GaN Transistors,” IEEE Electron Device Lett., 27(2006) 529.
[16] C. Zhou et al., ”Schottky-Ohmic Drain AlGaN/GaN Normally Off HEMT With Reverse Drain Blocking Capability,” IEEE Electron Device Lett., 31(2010) 668.
[17] C. Zhou et al., “Self-Protected GaN Power Devices with Revese Drain Blocking and Forward Current Limiting Capabilities,” in Proc. ISPSD, 2010.
[18] S. Yoshida et al., “AlGaN/GaN Field Effect Schottky Barrier Diode for a Low Loss Switching Device,” Mater, Res. Soc. Symp. Proc., vol. 831, 2005.
[19] Y. Lin et al., ”Square-gate AlGaN/GaN HEMTs with improved trap-related characteristics,” IEEE Trans. Electron Devices, vol. 56, no. 12, pp. 3207-3211,2009.
[20] Y. Lin et al., “Schottky barrier height and nitrogen-vacancy-related defects in Ti alloyed,” J. Appl. Phys., vol. 95, 2004.
[21] D. Qiao et al., “Dependence of Ni/AlGaN Schottky barrier height on Al mole fraction,” J. Appl. Phys., vol. 87, 2000.
[22] N. Tsurumi et al., “AlN Passivation Over AlGaN/GaN HFETs for Surface Heat Spreading,” IEEE Trans. Electron Devices, vol. 57, no. 5, 2010.
[23] T. Hashizume et al., “Leakage mechanism in GaN and AlGaN Schottky interfaces,” Appl. Phys. Lett., vol 84, JUNE, 2004.