氮化鋁鎵/氮化鎵高速電子遷移率場效電晶體在用於高速和高功率開關應用引起了相當大的興趣，因為氮化鎵材料有傑出的電子特性包括二維電子(2DEG)電荷密度(>〖10〗^13 〖cm〗^(-2))、高導熱係數(>2 W〖cm〗^(-1) K^(-1))和高崩潰電場(3.3 MV/cm)。這些特性使氮化鋁鎵/氮化鎵元件崩潰電壓可以到達百伏特或千伏特。然而，對高功率元件的可靠性與穩定性來說表面漏電流是一個嚴重的問題。
本論文提出兩個方法來解決由表面缺陷造成表面漏電流問題:(1) 先鈍化層製程 (2) 氮氣電漿處理在陰極跟飄移區域。這兩種方法用來保護表面，避免在做歐姆接觸時，所使用高溫退火而在表面形成氮氣空位缺陷。
首先，先鈍化層製程方法可以減少表面漏電流二個級數(從〖10〗^(-9) mA 到 〖10〗^(-11) mA)。片電阻可以降低70%。氮氣電漿處理在陰極造成導通電壓下降，對掘入12奈米深的陰極從0.68V到0.4V，對掘入30奈米深的陰極從0.52V到0.16V，我們也討論氮氣電漿處理瓦數對元件的影響，高瓦數的氮氣電漿處理在陽極，導通電壓降低，逆偏漏電流稍微減少。另外一方面，氮氣電漿處理在飄移區域可以減少逆向漏電流。

AlGaN/GaN HEMT have attracted considerable interests for high speed and high power switching application due to the outstanding electronic properties including high sheet charge density (>1013 cm-2) of the two dimensional electron gas (2DEG), high thermal conductivity of GaN (>2 Wcm-1k-1) and high breakdown field (3.3 MV/cm), which allows to fabricate devices with breakdown voltages in the order of hundreds and even up to thousands of volts. However, one of the most critical issues to be solved is the surface leakage current, which is mainly related to reliability and stability for power electronics applications.
This thesis focuses on AlGaN/GaN heterojunction Schottky barrier diodes (SBDs) on Si substrate for power electronics applications. For high power applications, the surface control process was investigated to suppress leakage current in GaN-on-Si devices by using two different approaches, including a passivation first process and a nitrogen plasma treatment process. Both two approaches are proposed to protect surface from producing N-vacancy defects during high temperature annealing for ohmic contact formation and further suppress the leakage current by recovering nitrogen-vacancy-related defects.
First, a passivation first approach is proposed to reduce the surface leakage current from ~10-9 A to ~10-11 A and reduce the sheet resistance up to 70% compared with the SBDs without passivation first. Second, the devices with the nitrogen plasma treatment show a reduced VON from 1 V to 0.7 V for 12-nm recess SBDs and a reduced VON from 0.8 V to 0.4 V for 30-nm recess SBDs, comparing with that of the devices without nitrogen plasma treatment. We also investigated the impact of the plasma power on the device characteristics. With a higher power of plasma treatment on anode region, the turn-on voltage can be reduced with slightly degradation of reverse leakage current. On the other hand, the plasma treatment on the drift region could reduce the reverse leakage current.

ABSTRACT ii
中文摘要 iv
ACKNOWLEDGEMENT v
CONTENTS vi
LIST OF FIGURE ix
LIST OF TABLE xii
Chapter1 1
Introduction 1
1.1 Research Background 1
1.2 Thesis Organization 3
Chapter 2 4
Basic of Concepts of GaN Material and Measurements 4
2.1 Basic of GaN Material 4
2.1.1 Wide bandgap materials 5
2.1.2 Saturation electron velocity 6
2.1.3 Breakdown voltage versus on-resistance 7
2.1.4 Two-Dimensional Electron Gas (2DEG) 9
2.2 Measurements 11
2.2.1 Transfer Length Method (TLM) 11
2.2.2 Surface leakage current measurements 14
2.3 Summary 15
Chapter 3 16
AlGaN/GaN Schottky Barrier Diodes with Passivation First Process 16
3.1 AlGaN /GaN SBDs 16
3.2 Device design 16
3.3 Process flows 17
3.3.1 Mesa isolation 18
3.3.2 SiN passivation 19
3.3.3 Ohmic contact 20
3.3.4 Schottky contact 23
3.3.5 Removal of SiN film passivation 24
3.4 Results and Discussions 26
3.4.1 Transfer Length Method (TLM) 27
3.4.2 Surface leakage 33
3.4.3 Forward current 36
3.4.4 Reverse leakage current 41
3.5 Summary 42
Chapter 4 43
AlGaN/GaN Schottky Barrier Diode with Nitrogen Plasma Treatments 43
4.1 AlGaN/GaN SBDs with nitrogen plasma treatment 43
4.2 Device Design 44
4.3 Process flows 44
4.3.1 Mesa isolation 45
4.3.2 Ohmic contact 46
4.3.3 Anode recess and Nitrogen plasma treatment under anode 46
4.3.4 Schottky contact 48
4.3.5 Nitrogen plasma treatment in drift region. 49
4.3.6 SiN/SiO2/SiN passivation 49
4.3.7 Via 51
4.4 Results and Discussions 51
4.4.1 Forward characteristics 52
4.4.2 Reverse leakage current 58
4.4.3 Sheet resistance 64
4.5 Summary 65
Chapter 5 66
Conclusions and Future Works 66
Chapter 6 68
References 68

[1] T. Hashizume et al., “Leakage mechanism in GaN and AlGaN Schottky interfaces,” Appl. Phys. Lett., vol. 84, no. 24, pp.4884-4886, Jun. 2004.
[2] E. Miller et al., “Analysis of reverse-bias leakage current mechanisms in GaN grown by molecular-beam epitaxy,” Appl. Phys. Lett., vol. 84, no. 4, pp.535-537, Jan. 2004.
[3] C. YongHe et al., “Study of surface leakage current of AlGaN/GaN high electron mobility transistors,” Appl. Phys. Lett., vol. 104, no. 15, pp. 153509-153509-4, Apr. 2014.
[4] T. Hashizume et al., “Large reduction of leakage currents in AlGaN Schottky diodes by a surface control process and its mechanism,” Journal of Vacuum Science & Technology B, vol. 24, no. 4, pp. 2418-2155, Jul. 2006.
[5] A. Edwards et al., “Improved reliability of AlGaN-GaN HEMTs using an NH3 plasma treatment prior to SiN passivation,’’ Electron Device Letters, IEEE., vol. 26, issue 4, pp. 225-227, Apr. 2005.
[6] J. Chung et al., “Effect of gate leakage in the subthreshold characteristics of AlGaN/GaN HEMTs,’’ Electron Device Letters, IEEE., vol. 29, issue 11, pp. 1196-1198, Nov. 2008.
[7] C. Rongming et al., “Plasma treatment for leakage reduction in AlGaN/GaN and GaN Schottky contacts,’’ Electron Device Letters, IEEE., vol. 29, issue 4, pp. 297-299, Apr. 2008.
[8] G. Vanko et al., “Impact of SF6 plasma on dc and microwave performance of AlGaN /GaN HEMT structures,’’ Advanced Semiconductor Devices and Microsystems (ASDAM), pp. 335-338, Oct. 2008.
[9] L. Shih-Chien et al., “GaN MIS-HEMTs with nitrogen passivation for power device applications,’’ Electron Device Letters, IEEE, vol. 35, issue. 10, pp. 1001-1003, Oct. 2014.
[10] L. Yu-Syuan et al., “Improved trap-related characteristics on SiNx/AlGaN/GaN MISHEMTs with surface treatment,’’ Power Semiconductor Devices & IC's (ISPSD), pp.293-296, Jun. 2014.
[11] O. Ambacher et al., “Growth and applications of group III-nitrides,” Journal of
Physics D (Applied Physics), vol. 31, pp. 2653-2710, 1998.
[12] B. J. Baliga, “Power Semiconductors Devices,” Boston: PWS, pp. 28-29, 1996.
[13] M. Willander et al., “Silicon carbide and diamond for high temperature devices
applications,” Journal of materials science: materials in electronics, pp. 1-25,
2006.
[14] B. Gelmont et al., “Monte Carlo simulation of electron transport in gallium
nitride,” J. Appl. Phys., vol. 74, no. 3, pp. 1818-1821, 1993.
[15] O. Ambacher, “Growth and applications of Group III-nitrides,” J. Phys. D: Appl. Phys. 31 (1998) 2653–2710.
[16] B.J. Baliga, “Semiconductors for high voltage vertical channel field effect transistors, ” J.Appl Phys , vol 53, pp 1759-1764, 1982.
[17] Jerry L. Hudgins et al., “An assessment of wide bandgap semiconductors for power devices, ” IEEE Transactions on power electronics, Vol. 18, No. 3, May. 2003.
[18] O. Ambacher et al., “Two-dimensional electron gases induced by spontaneous and piezoelectric polarization charges in N- and Ga-face AlGaN/GaN heterostructures,’’ Journal of Applied Physics, vol. 85, num. 6, Mar. 1999.
[19] W. Tan et al., “Surface leakage currents in SiNx passivated AlGaN/GaN HFETs,’’ Electron Device Letters, IEEE, vol. 27, issue 1, pp1-3, Jan.2006.
[20] T. Hashizume et al., ‘‘Effects of nitrogen deficiency on electronic properties of AlGaN surfaces subjected to thermal and plasma processes,’’ Applied Surface Science, vol.234, pp. 387-394, 2004.
[21] B. Boudart et al., “Raman characterization of Mg+ ion-implanted GaN,” J. Phys. Condens Matter, vol. 16, no. 2, pp. s49-s55, Jan. 2004.
[22] T. Oishi et al., “Highly resistive GaN layers formed by ion implantation of Zn along the c-axis,” J. Appl. Phys., vol. 94, no. 3, pp. 1662-1666, Aug. 2003.
[23] J. Y. Shiu et al., “Oxygen ion implantation isolation planar process for AlGaN/GaN HEMTs,” IEEE Electron Device Letter, vol. 28, no. 6, pp. 476-478, Jun. 2007.
[24] G. Koleyet et al., “Slow transients observed in AlGaN/GaN HFETs: effects of SiNx passivation and UV illumination,” IEEE Trans. Electron Devices, vol. 50, no. 4, pp. 886-893, Apr. 2003.
[25] S. Huang et al., “Effective passivation of AlGaN/GaN HEMTs by ALD-grown AlN think film,” IEEE Electron Device Lett., vol. 33, no. 4, pp. 516–518, Apr. 2012.
[26] R. C. Fitc et al., “Comparison of passivation layers for AlGaN/GaN high electron mobility transistors,” J. Vac. Sci. Technol., B, vol. 29, no. 6, pp. 061204, Oct. 2011.
[27] Y. Lin et al., “Schottky barrier height and nitrogen-vacancy-related defects in Ti alloy,” J. Appl. Phys., vol. 95, Jun. 2004.
[28] M. Hiroki et al., “Al/Ti/Al Ohmic contact to AlGaN/GaN heterostructure,” IEICE Technical Report ED, vol. 108, no. 34, pp. 51-56, May. 2008.
[29] R. Gong et al., “Analysis on the new mechanisms of low resistance stacked Ti/Al Ohmic contact structure on AlGaN/GaN HEMTs,”J.Phys. D: Appl. Phys., vol. 43, no. 39, pp. 1562-1564, Oct. 2010.
[30] Jui-Ming Yang, M. D. 2012. Design and Fabrication of High Power GaN-Based HEMTs and Schottky Barrier Diodes on Silicon Substrates, National Tsing Hua University, Institute of Electronics Engineering.
[31] L. Wang et al., “Direct contact mechanism of ohmic metallization to AlGaN/GaN heterostructures via ohmic area recess etching,” Applied Physics Letters., vol. 95, pp. 172107-172107-3, Jun. 2009.
[32] K. Shiojima et al., “Systematic study of thermal stability of AlGaN/GaN two dimensional electron gas structure with SiN surface passivation,’’ IEICE Electronics Express., vol. 1, pp. 160-164, Jun. 2004.
[33] Z. T. Chen et al., “Pd/InAlN Schottky diode with low reverse current by sulfide treatment,’’ Appl. Phys. Lett., vol. 99, issue 18, Mar. 2011.
[34] M. Romero et al., “Impact of N2 plasma power discharge on AlGaN/ GaN HEMT Performance,’’ Electron Devices, IEEE Transactions., vol. 59, issue 2, pp.374-379, Feb. 2012.
[35] A. Edwards et al., “Improved reliability of AlGaN-GaN HEMTs using an NH3 plasma treatment prior to SiN passivation,’’ Electron Device Letters, IEEE., vol. 26, issue 4, pp. 225-227, April. 2005.
[36] J. Chung et al., “Effect of gate leakage in the subthreshold characteristics of AlGaN/GaN HEMTs,’’ Electron Device Letters, IEEE., vol. 29, issue 11, pp. 1196-1198, Nov. 2008.
[37] C. Rongming et al., “Plasma treatment for leakage reduction in AlGaN/GaN and GaN schottky contacts,’’ Electron Device Letters, IEEE., vol. 29, issue 4, pp. 297-299, Arpil. 2008.
[38] G. Vanko et al., “Impact of SF6 plasma on DC and microwave performance of AIGaN/GaN HEMT structures,’’ Advanced Semiconductor Devices and Microsystems (ASDAM), pp. 335-338, Oct. 2008.
[39] K. Kim et al., “Effects of TMAH treatment on device performance of normally off Al2O3/GaN MOSFET,’’ Electron Device Letters, IEEE, vol. 32, issue 10, pp. 1376-1378, Oct. 2011.
[40] J. Ibbetson et al., “Polarization effect, surface states, and the source of electrons in AlGaN/GaN heterojunction field effect transistors,” Applied physics letters, vol. 77, no. 2, Jun. 2000.
[41] G. Koleyet et al., “Slow transients observed in AlGaN/GaN HFETs: Effects of SiNx passivation and UV illumination,” IEEE Trans. Electron Devices, vol. 50, no. 4, pp. 886-893, Apr. 2003.
[42] S. Huang et al., “Effective passivation of AlGaN/GaN HEMTs by ALD-grown AlN think film,” IEEE Electron Device Lett., vol. 33, no. 4, pp. 516–518, Apr. 2012.
[43] R. Fitch et al., “Comparison of passivation layers for AlGaN/GaN high electron mobility transistors,” J. Vac. Sci. Technol., B, vol. 29, no. 6, pp. 061204, Oct. 2011.
[44] S. Linkohr et al., “Influence of plasma treatments on the properties of GaN/AlGaN/GaN HEMT structures,’’ Solid State Physics, vol. 9, issue 3-4, pp. 1096-1098, Mar. 2012.
[45] L. Yu-Syuan et al., ‘’Improved trap-related characteristics on SiNx/AlGaN/GaN MISHEMTs with surface treatment,’’ Power Semiconductor Devices & IC's (ISPSD), pp.293-296, June. 2014.
[46] Y. Yao et al., “Current transport mechanism of AlGaN/GaN Schottky barrier diode with fully recessed schottky anode,” Japanese Journal of Applied Physics, vol. 54, Jan. 2015.