在本篇論文中，利用成長在矽基板上的氮化鋁鎵/氮化鎵製作鰭狀高電子遷移率電晶體，期望達成增強式元件。鰭狀高電子遷移率電晶體不僅能使元件的臨界電壓往正的方向移動，還能使元件的電流密度與特徵電阻隨著鰭狀閘極的寬度微縮而有所提升。
在設計的原件中，具蕭特基閘極且寬度為兩微米元件的臨界電壓為-2.1伏但其臨界電壓並為隨著閘極寬度的微縮而上升。儘管如此，元件的電流密度與特徵電阻由平面式閘極的757 mA/mm與4.61 Ω-mm提升到1339 mA/mm與2.11 Ω-mm。而金氧半閘極的元件具有同樣的臨界電壓趨勢與更佳順偏特性，其電流密度與特徵電阻分別為1791 mA/mm與 2.1 Ω-mm。除此之外，鰭狀閘極的順偏特性不易受閘極與源極的距離所影響，其原因為鰭狀閘極有較高的接觸電阻。
除了提升順偏特性以外，鰭狀閘極並未裂化元件的逆偏特性包含閘極、源極漏電流與崩潰電壓儘管部分的閘極區域被蝕刻。蕭特基閘極元件的源極與閘極漏電流密度數量級分別為10-4 和101 mA/mm在閘極偏壓分別為-10伏與3伏下。而金氧半閘極原件能抑制閘級漏電流密度至10-4 mA/mm的數量級在相同閘極偏壓下。蕭特基閘極元件的崩潰電壓為845伏，其已達到許多功率應用的標準；而金氧半元件的崩潰電壓受到閘極絕緣層與鈍化層的薄膜品質引響，僅有470伏。與順偏特性相反，鰭式閘極的崩潰電壓仍隨著閘極與源極的距離增加而上升。

In this study, we to fabricate AlGaN/GaN Fin-HEMT devices to achieve enhancement mode operation. Besides the possibility to positive shift the threshold voltage, the device on-state performance including current density and specific on resistance can also be improved by scaling down the fin width.
Above our design, Schottky gate device with fin width = 2 μm has threshold voltage of -2.1 V but it does not positive shift compare to device without fin gate (planer device). Unlike threshold voltage, the current density and specific on resistance are greatly improve by the scaling down of the fin width which is 1339 mA/mm and 2.11 Ω-mm respectively compare to planer device 757 mA/mm, 4.61Ω-mm. MIS gate device has the same trend as Schottky gate device and even better on-state performance where the current density and specific on resistance are 1791 mA/mm and 2.1 Ω-mm. Furthermore, unlike planer HEMT device, weak LGD dependence to on-state performance is observed due to the increase of access resistance at gate region.
Beside the improved on-state characteristic, off-state performance includes gate, drain leakage and breakdown voltage are not degraded by fin gate process even though partial gate region of Fin-HEMT device are etched. The drain and gate leakage density are at the order of 10-4 and 101 mA/mm at gate voltage = -10 V and 3 V for Schottky gate device respectively, the MIS gate devices can improve the gate leakage which is 10-4 mA/mm under same bias condition. The breakdown voltages of Schottky gate is 845 V which meets the requirement in most of the power application. MIS gate Fin-HEMT suffer from the film quality of interface between gate insulator and passivation layer so its breakdown voltage is only 470 V. Unlike on-state characteristic, Breakdown voltage still increase with longer LGD.

摘要 I
ABSTRACT II
致謝 IV
TABLE OF CONTENTS V
LIST OF FIGURES VII
LIST OF TABLES X
CHAPTER 1 INTRODUCTION 1
1.1 Research background 1
1.2 Formation of Two-Dimensional Electron Gas 4
1.3 Motivation 6
CHAPTER 2 GaN-BASED HIGH ELECTRON MOBILITY TRANSISTORS 7
2.1 Structure of high mobility transistors 7
2.1.1 Choose of the substrate 7
2.1.2 Epitaxy structure 8
2.2 Operation Principle of HEMT 12
2.3 Concept of Fin-HEMT 13
CHAPTER 3 DESIGN AND FABRICAITON OF AlGaN/GaN FIN-HEMTs 15
3.1 Epitaxial structure 15
3.2 Device layout design 16
3.2.1 Schottky gate Fin-HEMT 16
3.2.2 MIS gate Fin-HEMT 18
3.3 Process flow for MIS gate Fin-HEMT 18
CHAPTER 4 RESULT AND DISCUSSION 26
4.1 Electrical Performance of AlGaN/GaN Epistructure 26
4.1.1 Hall Measurement 26
4.1.2 Transmission Line Model (TLM) Measurement 27
4.2 Schottky Gate AlGaN/GaN Fin-HEMT 31
4.2.1 Current Voltage characteristics 31
4.2.2 Off-state characteristics 36
4.3 Metal-Insulator-Semiconductor AlGaN/GaN Fin-HEMT 40
4.3.1 Current Voltage characteristics 40
4.3.2 Off-state characteristics 44
CHAPTER 5 CONCLUSION AND FUTURE WORK 47
5.1 Conclusions 47
5.2 Future work 48
Reference 49

[1] A. Nakagaw, Y. Kawaguchi, and K. Nakamura, “Silicon Limit Electrical Characteristics of Power Devices and ICs,” Ieice Trans. Electron. E Ser. C, vol. 84, pp. 1462–1469, 2001.
[2] B. J. Baliga, “Power Semiconductor Device Figure of Merit for High-Frequency Applications,” IEEE Electron Device Lett., vol. 10, no. 10, pp. 455–457, 1989.
[3] A. Bykhovski, B. Gelmont, and M. Shur, “The influence of the strain-induced electric field on the charge distribution in GaN-AlN-GaN structure,” J. Appl. Phys., vol. 74, no. 11, pp. 6734–6739, 1993.
[4] F. Sacconi, A. Di Carlo, P. Lugli, and H. Morkoç, “Spontaneous and piezoelectric polarization effects on the output characteristics of AlGaN/GaN heterojunction modulation doped FETs,” IEEE Trans. Electron Devices, vol. 48, no. 3, pp. 450–457, 2001.
[5] O. Ambacher et al., “Two-dimensional electron gases induced by spontaneous and piezoelectric polarization charges in N- And Ga-face AIGaN/GaN heterostructures,” J. Appl. Phys., vol. 85, no. 6, pp. 3222–3233, 1999.
[6] B. Leung, J. Han, and Q. Sun, “Strain relaxation and dislocation reduction in AlGaN step-graded buffer for crack-free GaN on Si (111),” Phys. Status Solidi Curr. Top. Solid State Phys., vol. 11, no. 3–4, pp. 437–441, 2014.
[7] T. Ide et al., “Improvement of DC characteristics in AlGaN/GaN heterojunction field-effect transistors employing AlN spacer layer,” Japanese J. Appl. Physics, Part 1 Regul. Pap. Short Notes Rev. Pap., vol. 41, no. 9, pp. 5563–5564, 2002.
[8] W. Saito et al., “Switching controllability of high voltage GaN-HEMTs and the cascode connection,” in Proceedings of the International Symposium on Power Semiconductor Devices and ICs, 2012.
[9] K. Ohi, J. T. Asubar, K. Nishiguchi, and T. Hashizume, “Current stability in multi-mesa-channel AlGaN/GaN hemts,” IEEE Trans. Electron Devices, vol. 60, no. 10, pp. 2997–3004, 2013.
[10] D. S. Lee et al., “Nanowire Channel InAlN/GaN HEMTs With High Linearity of gm and fT,” IEEE Electron Device Lett., vol. 34, no. 8, pp. 969–971, Aug. 2013.
[11] H. Zhou, X. Lou, S. B. Kim, K. D. Chabak, R. G. Gordon, and P. D. Ye, “Enhancement-Mode AlGaN/GaN Fin-MOSHEMTs on Si Substrate With Atomic Layer Epitaxy MgCaO,” IEEE Electron Device Lett., vol. 38, no. 9, pp. 1294–1297, Sep. 2017.
[12] K. Ren, Y. C. Liang, and C. F. Huang, “Compact Physical Models for AlGaN/GaN MIS-FinFET on Threshold Voltage and Saturation Current,” IEEE Trans. Electron Devices, vol. 65, no. 4, pp. 1348–1354, 2018.