| 摘要: | 氮化鎵 (GaN) 基高電子遷移率電晶體 (HEMT) 的開發徹底改變了電力電子領域，與傳統矽基元件相比，在效率、開關速度和熱性能方面具有顯著優勢。這博士論文對先進 GaN HEMT 結構進行了全面研究，特別關注增強常關（E 模式）元件的性能，這對於功率開關應用至關重要。
在這項工作中，我們研究了幾種新穎的元件架構和製造技術，旨在克服與 GaN HEMT 相關的固有p-GaN閘極挑戰。以下研究概述了本研究的主要貢獻：
具有薄 AlGaN 障礙層 HEMT 的擴展 p-GaN 閘極：本研究研究了具有擴展 p-GaN 的常斷 p-GaN/AlGaN/GaN HEMT。 p-GaN 擴展區域下方的 AlGaN 障礙層中的最佳化凹陷深度提供了改進的元件特性。模擬研究了AlGaN障礙層凹陷深度和p-GaN延伸區的延伸長度對閥值電壓(VTH)、最大漏極電流(ID,MAX)和崩潰電壓(BV)的影響。與沒有p-GaN 擴展的元件相比，所提出的具有1 μm p-GaN 擴展和AlGaN 障礙層中2 nm 凹槽深度的電晶體在VTH 和ID,MAX 方面有所改進，而不會降低崩潰電壓。
常關 p-GaN 閘極 AlGaN/GaN HEMT，具有新的蕭特基第二柵極。本研究提出了一種常斷雙閘極 AlGaN/GaN HEMT。第二閘極位於p-GaN閘極和汲極之間並連接到源極。 p-GaN 旁的第二個閘極下方的 AlGaN 層的最佳化厚度和長度顯著影響 ID,MAX和關閉擊穿條件。由於在第二閘極和汲極之間建立了反向電流的續流路徑，以防止元件負偏壓時出現過大的壓降和導通損耗，因此反向導通特性也得到改善。與傳統的HEMT相比，所提出的方法顯示了一種可行的方法來實現具有優異正向和反向傳導性能的常斷GaN基HEMT。
具有 p-GaN 延伸閘極的 AlGaN/GaN HEMT，可改善電流分散和擊穿特性：本研究介紹了一種獨特的 p 型 GaN 閘極 AlGaN/GaN HEMT 配置。在這個設計中，p-GaN 區域向具有原始柵電極的汲極延伸。這項創新顯著增強了 HEMT 的性能，與傳統 p-GaN 閘極 HEMT 相比，崩潰電壓 (BV) 提高了 45.2%，VTH 提高了 17%。延伸閘極設計重新分佈電場，充當場板以提高崩潰電壓。此外，所提出的元件透過在不增加 RON 的情況下減少 17.4% 的飽和電流，可能提供改進的短路能力。
p-GaN AlGaN/GaN HEMT 磊晶層中的障礙層肖特基二極體：這項工作研究了將AlGaN/GaN 肖特基二極體與p- 並聯放置而創建的障礙層肖特基（偽JBS）二極體。這種偽JBS二極體利用二維電子氣來增加工作電流，從而降低RON。所製造的陽極至陰極長度(LAC) 為10 μm 的偽JBS 二極體顯示出1.05 V 的開啟電壓、2.53 mΩ-cm2 的最小
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比RON (RON,MIN) 和1112 V 的崩潰電壓，從而產生了優異的性能。這項研究為肖特基障礙層二極體提供了一種有前景的替代品，無需額外的 p-GaN 層設計。
結合MIS 和p-GaN 閘極結構的新閘極設計，可實現常關和高導通電流操作：本研究提出了一種新的閘極架構，整合了p-GaN 閘極和金屬-絕緣體-半導體(MIS) 結構，可實現常關和高導通操作。 Silvaco TCAD 模擬軟體用於評估所提議設計的性能。對元件的傳輸、輸出和崩潰特性進行了全面分析，並與傳統的 p-GaN 閘極 AlGaN/GaN HEMT 進行了比較。研究結果表明，將 MIS 與 p-GaN 閘極結合可以增加通態電流密度並降低 RON。所提出的 HEMT 表現出優越的屬性，與傳統的 p-GaN 閘極 HEMT 相比，漏極電流增加了 80%，但仍與 VTH 和 BV 相似。因此，與傳統的 p-GaN 閘極 HEMT 相比，所提出的 HEMT 表現出更高的電流密度並增強了對通道的閘極控制，而無需修改 VTH.
在整個論文中，我們結合了實驗技術、先進的製造流程和全面的模擬來驗證所提出的新設計。對 VTH 穩定性、RON、電流崩潰和 BV 等關鍵性能指標進行系統分析和最佳化。這項研究的結果有助於推動基於 GaN 的功率元件的進步，為元件設計和製造提供新的見解。所提出的結構展示了增強 GaN HEMT 性能和可靠性的巨大潛力，為其在高功率和高頻應用中的提供可能性方案。本文最後討論了未來的工作，並強調了進一步改進和探索的潛在領域。其中包括先進材料的整合、元件尺寸的縮放以及開發新的表面製程技術，以充分利用 GaN HEMT 在下一代電力電子元件中的功能。;The development of Gallium Nitride (GaN)-based High Electron Mobility Transistors (HEMTs) has revolutionized the field of power electronics, offering significant advantages in terms of efficiency, switching speed, and thermal performance over traditional silicon-based devices. This Ph.D. thesis presents a comprehensive study of advanced GaN HEMT structures, with a particular focus on enhancing the performance of normally-off (E-mode) devices, which are crucial for power switching applications.
In this work, we investigate several novel device architectures and fabrication techniques aimed at overcoming the inherent challenges associated with GaN HEMTs. The primary contributions of this research are outlined in the following studies:
Extended p-GaN gate with thin AlGaN barrier HEMTs: This study investigated a normally-off p-GaN/AlGaN/GaN HEMT with the extended p-GaN. The optimized recess depth in the AlGaN barrier under the extended region of p-GaN provides improved device characteristics. The influences of recess depth in the AlGaN barrier and the extended length of the p-GaN extension on the threshold voltage (VTH), the maximum drain current (ID,MAX), and breakdown voltage (BV) were simulated and studied. The proposed transistor with a 1-μm p-GaN extension and 2-nm recess depth in AlGaN barrier shows improvement on VTH and ID,MAX without degrading the breakdown voltage compared with the device without p-GaN extension.
Normally
O ff p GaN g ate AlGaN/GaN HEMT with a n ew s chottky s econd g ate This study presents a normally-off dual-gate AlGaN/GaN HEMT. The second gate is located between the p-GaN gate and the drain and is connected to the source. The optimized thickness and length of the AlGaN layer under the second gate next to the p-GaN significantly impact the I D,MAX and the off-state breakdown conditions. The reverse conduction characteristic is also improved because the freewheeling path of the reverse current is established between the second gate and the drain to prevent excessive voltage drop and conduction losses when the device is negatively biased. Compared with conventional HEMT, the proposed method shows a promising way to achieve normally-off GaN-based HEMTs with excellent forward and reverse conduction performance.
An AlGaN/GaN HEMT with p
GaN e xtended g ate for i mprovements on c urrent d ispersion and
b reakdown c haracteristics: This study introduces an unique p-type GaN gate AlGaN/GaN
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HEMT configuration. In this design, the p-GaN region extends toward the drain with an original gate electrode. This innovation significantly enhances the HEMT’s performance, with a 45.2% increase in breakdown voltage (BV) and a 17% higher VTH compared to conventional p-GaN gate HEMTs. The extended gate design redistributes the electric field, acting as a field plate to elevate the breakdown voltage. Furthermore, the proposed device, by reducing 17.4% of the saturation current without increasing the RRONON, possibly offers improved short-circuit capability.
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A ppseudoseudo--jjunction unction bbarrier Schottky arrier Schottky ddiode in piode in p--GaN AlGaN/GaN GaN AlGaN/GaN HEMT eHEMT epitaxial pitaxial llayers:ayers: This work investigates a pseudo-junction barrier Schottky (pseudo-JBS) diode that is created by placing an AlGaN/GaN Schottky diode in parallel with a p-GaN junction on the same epitaxial p-GaN gate AlGaN/GaN HEMT wafer. This pseudo-JBS diode employs the two-dimensional electron gas to increase the operation current, thus reducing the RRONON with high blocking voltage. The fabricated pseudo-JBS diode with anode-to cathode lengths (LAC) of 10μm shows a turn-on voltage of 1.05 V, a minimum specific RRONON (RON,MIN) of 2.53mΩ cm2, and blocking voltage of 1112 V yielding an excellent Baliga’s figure of merit of 488.7MWcm-2 on the same epitaxial p-GaN/AlGaN/GaN HEMT wafer. This study provides a promising substitute for Schottky barrier diodes without requiring extra p-GaN layer design.
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A nnew ew ggate ate ddesign esign ccombining MIS and pombining MIS and p--GaN GaN ggate ate sstructures for tructures for nnormallyormally--ooff and ff and hhigh igh oonn--ccurrent urrent ooperation: peration: This study proposes a new gate architecture that integrates both a p-GaN gate and a metal–insulator–semiconductor (MIS) structure for a normally-off AlGaN/GaN HEMT. Silvaco TCAD simulation software is used to assess the performance of the proposed design. A comprehensive analysis of the device’s transfer, output, and breakdown characteristics is carried out and compared with the conventional p-GaN gate AlGaN/GaN HEMT. The findings indicate that incorporating MIS in conjunction with the p-GaN gate leads to an augmentation in the on-state current density and a reduction in RRONON. The proposed HEMT exhibits superior attributes, with an 80% increase in drain current compared to the conventional p-GaN gate HEMT, but remains similar to VTH and BV. Consequently, the proposed HEMT demonstrates elevated current density and enhances gate control over the channel without modifying the VTH compared to the conventional p-GaN gate HEMT
Throughout this thesis, we employ a combination of experimental techniques, advanced fabrication processes, and comprehensive simulations to validate the proposed designs. Key performance metrics such as VTH stability, RON, current collapse, and BV are systematically analyzed and optimized. The findings of this research contribute to the advancement of GaN-based power devices, providing new insights into device design and fabrication. The proposed
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structures demonstrate significant potential for enhancing the performance and reliability of GaN HEMTs, paving the way for their broader adoption in high-power and high-frequency applications. This thesis concludes with a discussion of future work, highlighting potential areas for further improvement and exploration. These include the integration of advanced materials, scaling of device dimensions, and the development of new characterization techniques to fully exploit the capabilities of GaN HEMTs in next-generation power electronics. |
