在本論文中，我們提出混合式閘極掘入研製氮化鋁鎵/氮化鎵材料為基礎之增強型高電子移動率電晶體。由於氮化鋁鎵/氮化鎵結構具有濃厚的二維電子氣使元件保持在常開的狀況，我們利用閘極掘入方式減少閘極金屬與二維電子氣之距離，使臨界電壓達到正偏移，並將二氧化鉿作為介電層進而提高元件之特性。此外，利用無電鍍沉積法、預植晶種技術以及過氧化氫表面處理技術，完整探討其對元件之影響，包含直流及熱穩定度。實驗結果顯示，所研製的元件展現出良好的特性以及高溫操作能力。
首先，以混合式閘極掘入研製出具增強型操作之氮化鎵/氮化鋁鎵異質結構場效應電晶體。混合式閘極掘入技術包含乾式蝕刻及濕式蝕刻，此技術縮短閘極金屬與通道之間的有效距離使得臨界電壓產生正偏移。接著，利用蒸鍍的方式鍍上不同種類之閘極金屬研製氮化鎵/氮化鋁鎵異質結構場效應電晶體並作比較。此外，我們利用射頻磁控濺鍍沉積二氧化鉿，在鈀/氮化鎵間形成良好的介電層。由於二氧化鉿高介電係數之特性，所形成的介電層可以降低表面能態及抑制電流崩塌。從實驗結果可發現，處理後之電晶體可調變成具增強型操作之增強型操作元件。最後，將所研製電晶體針對不同溫度做相關特性的分析。
其次，以低溫無電鍍鈀沉積法結合混合式閘極掘入研製出具增強型操作之氮化鎵/氮化鋁鎵異質結構場效應電晶體。藉由無電鍍低溫與低能量的沉積特性，能減少蕭特基接面之熱破壞及表面態位密度。從實驗的結果得知，相較於蒸鍍閘極元件，無電鍍閘極元件顯示具有較佳的蕭特基接面特性與優異的直流特性。另外，我們探討不同溫度無電鍍閘極元件的各種相關特性表現。
最後，利用過氧化氫表面處理增強型氮化鎵/氮化鋁鎵異質結構場效應電晶體。藉由將元件浸泡至過氧化氫溶液，在表面產生一薄膜氧化鋁層，然後，以射頻磁控濺鍍的方式沉積二氧化鉿，形成二氧化鉿/氧化鋁之堆疊式的介電層之結構，此結構不但能降低表面耐態也能使閘極漏電流大幅下降。

In this dissertation, we report hybrid gate recess technique to fabricate Enhancement-Mode AlGaN/GaN High Electron Mobility Transistors (HEMTs). Owing to the dence Two Dimensional Electron Gas (2DEG) of AlGaN/GaN structures, the device was normally-on at zero gate-source voltage. We used gate recess technique to reduce the distance between the gate and 2DEG layer, which can effectively shift the threshold voltage to positive. The Hf¬O2 are served as a gate dielectric layer, which can improve the performance of devices. By electroless plating (EP) deposition approach, pre-seeding metal seeds approach and hydrogen peroxide surface treatment, the device characteristic of the DC performance and temperature stability are investigated. Experimentally, the studied devices show good device characteristics and high temperature operation capability.

First, an E-mode AlGaN/GaN heterostructure field-effect transistor (HFET), using hybrid gate recess technology, is fabricated and investigated. Hybrid gate recess technique incorporating dry etching technique and wet etching technique can effectively reduce the distance between metal gate and 2DEG layer. A distance reduction between the gate and channel layer resulted in a positive shift in threshold voltage (Vth). Then, different metal was fabricated as gate of AlGaN/GaN HEMTs to make comprehension. In addition, a HfO2 dielectric was prepared by R.F sputtering is implemented. Due to the high dielectric constant of HfO2,the formed dielectric could decrease the surface state and suppress the current collapse. Experimentally, the treated HEMT is converted to an enhancement mode (E-mode) operation. Therefore, the improvement of device performance of DC and thermal stability could be expected.
Second, the enhancement mode AlGaN/GaN high electron mobility transistors (HEMTs), with hybrid gate recess, sensitization, activation, and electroless plating (EP) of palladium (Pd) deposition, are fabricated and studied. The employed sensitization and activation processes could reduce the deposition time of EP and form the uniform metal film. Hence, the improvement of device performance in terms of DC performance and thermal stability. Moreover, the lower temperature variation rate and thermal stability of device over range (300~500K) are obtained.
Finally, the enhancement mode AlGaN/GaN high electron mobility transistors (HEMTs), with hydrogen peroxide surface treatment, are fabricated and studied. The device was immersed in H2O2 to form a thin AlxOy. Then, the HfO2 was sputtered as a dielectric. Therefore, a stack dielectric structure of AlxOy/HfO2 is achieved in this work. The stack dielectric layer could reduce the gate leakage and decrease the surface state, which can improve the performance of device.

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