- 學位論文
增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體製作與電流崩潰特性分析
Fabrication and Current Collapse Characterizations of Enhancement-Mode AlGaN/GaN High Electron Mobility Transistors
摘要
氮化鋁鎵/氮化鎵高電子遷移率電晶體擁有高能帶及高電子遷移率的材料特性，使其大量應用於高電壓電子元件及高效率電源轉換系統。其異質接面所產生的大量二維電子氣提供元件大電流、低阻抗之元件特性，因而近年來越來越被重視。然而當元件在高速切換下，材料缺陷所造成的漏電流以及電流坍塌現象使得電晶體無法達到所預期之高效率電能轉換。本研究致力於增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體之研發及其動態電特性之分析。 本論文利用電漿輔助化學氣相沉積系統所沉積出的二氧化矽薄膜作為電晶體的鈍化層，藉此探討電流坍塌現象於p型氮化鎵高電子遷移率電晶體的影響與機制。實驗發現擁有二氧化矽鈍化層的電晶體有較優異的電流坍塌抗性。透過量測分析驗證鈍化層的內部缺陷提供額外的電子累積空間，避免電子累積在p型氮化鎵覆蓋層而空乏通道中二維電子氣之載子，有效減緩電流坍塌現象。 為了發展金氧半結構並達到元件特性最佳化，尤其直接影響電流坍塌現象的閘極漏電流，優良的材料介面品質為首要之條件，因此文中分別對於空乏型及增強型高電子遷移率電晶體，提出不同的介面處理包含氟離子電漿處理、氬氣及氮氣電漿轟擊以應用於將來金氧半結構介面品質之提升。 根據先前研究氮化鋁鎵/氮化鎵高電子遷移率電晶體的實驗經驗，我們發展金氧半結構並探討其電性，發現藉由原子層沉積系統所沉積出的氧化鋁能夠成功鈍化p型氮化鎵表面受到電漿轟擊所留下的缺陷，抑制長脈衝下的電流坍塌現象，進一步分析單、雙異質結構對於電性的影響及抑制電流坍塌效應之能力，發展出有效利用於p型氮化鎵金氧半高電子遷移率電晶體轉換效率提升之方法。
並列摘要
The applications of gallium nitride high electron mobility transistors (GaN HEMTs) have become more and more important in recent years. Due to the outstanding material properties including wide-band-gap and high electron mobility, GaN HEMTs are widely applied to high voltage electronics and high efficiency power conversion systems. The two dimensional electron gas (2DEG) formed in heterojunction ensures the large operating output current and low on-resistance of the device. However, the leakage current and current collapse phenomenon concerning to the material defects reduce the power conversion efficiency of the device in high speed switching. In this research, enhancement-mode (E-mode) AlGaN/GaN HEMTs are demonstrated; the electrical characteristics and dynamic characteristics are also investigated. In this thesis, dynamic output characteristics are analyzed between the conventional p-GaN HEMT and the HEMT with plasma enhanced chemical vapor deposition (PECVD) SiO2 as the passivation. The current collapse can be suppressed effectively in E-mode HEMT with SiO2 due to the extra electron-accumulating space created by passivation. Electrons that used to accumulate in p-GaN capping layer and deplete 2DEG carriers can be neutralized by electron-accumulating space formed in SiO2. In order to construct metal-insulator-semiconductor (MIS)-HEMTs with optimized performance, high quality of layer interface is the critical factor of current collapse suppression and gate leakage minimization. We propose surface treatments including fluorine plasma, argon plasma and nitrogen plasma to improve interface quality. Based on our previous experience of developing AlGaN/GaN HEMTs, we construct MIS structures with atomic layer deposition (ALD) Al2O3. The Al2O3 can passivate the surface defects formed by plasma bombardment and suppress current collapse in long pulse mode. Also, we investigate the impact of epi structures on electrical characteristics and the phenomenon of current collapse. The power conversion efficiency in p-GaN MIS-HEMTs can be effectively improved by double heterostructure.
參考文獻
延伸閱讀
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