本論文應用液相沉積法沉積高介電氧化層薄膜於氮化鎵材料上並研製為氮化鋁鎵/氮化鎵金氧半高電子移動率電晶體。液相沉積法是一便宜簡單的沉積方式，不需要外加額外的能量或電壓，且可於低溫下進行，減少熱應力造成的缺陷。數種不同的高介電氧化層包括二氧化鈦、鈦酸鍶及二氧化鋯皆以液相沉積法沉積於氮化鎵上並利用X射線光電子能譜、電子力顯微鏡等各項儀器進行化、物性分析。
使用高介電常數材料為閘極介電層可有效克服轉導下降及介電層過薄導致的穿遂電流問題。二氧化鈦、鈦酸鍶兩者均有相當高之介電常數(>60)，使用此兩種材料研製金氧半高電子移動率電晶體，與傳統高電子移動率電晶體相比，金氧半高電子移動率電晶體具有較小之漏電流，較高之崩潰電壓，且轉導與臨界電壓並為無大幅改變，此外亦能有效改善表面態位，降低界面散射。然而，此兩種材料具有能隙較低的缺點，為補足此缺陷，因此也以液相沉積法沉積二氧化鋯做為介電層，二氧化鋯具有不錯的介電常數(>20)以及高能矽(>6eV)，適合做為介電層使用。結果顯示使用約2奈米二氧化鋯為介電層之金氧半高電子移動率電晶體即可有效改善元件漏電流與崩潰特性。
具有高電流與高電壓的氮化鋁鎵/氮化鎵高電子移動率電晶體非常適合於於功率應用，然而散熱是一大問題，藉由使用高導熱的碳化矽基板，可以改善此問題，在本論文最後，將針對使用碳化矽基板的氮化鋁鎵/氮化鎵高電子移動率電晶體進行分析，並與使用矽基板的元件相比較，結果顯示使用碳化矽基板的元件具有較佳之特性，於1.2mm元件中，PAE可達38.4%而功率輸出為981mW。

The high-k materials were deposited on GaN and AlGaN/GaN MOSHEMTs were fabricated with high-k gate dielectrics. Liquid-phase-deposition (LPD) is a simple, low-cost method. It works without complicated equipments or any assisting energy source, and can be used at low temperature. The relatively low deposition temperature effectively avoids thermal strain and defects. Several different high-k materials, including TiO2, STO, and ZrO2, were deposited on GaN and analyzed by XPS, SEM, etc.
By using a high-k material as a gate dielectric, the decrease of transconductance and the tunneling current can be overcome by maintaining high gate-to-source capacitance and oxide thickness. TiO2 and STO both have quite high dielectric constant (>60). The MOSHEMTs using these 2 kinds of oxides show lower leakage current and larger breakdown voltage, compared with the counterpart HEMTs. There is no obviously change of transconductance and threshold voltage in the MOSHEMTs. The LPD oxides also improve surface states, and reduce influences from interface scattering. However, the bandgap of these two oxides is low, and this leads to the larger leakage current. To overcome this problem, ZrO2 was also deposited, due to its high dielectric constant (>20) and high bandgap (>6eV). It's demonstrated that the gate leakage current and breakdown characteristics can be improved in the AlGaN/GaN MOSJEMTs with 2 nm-thick ZrO2 show
The high current and high voltage for high power applications of AlGaN/GaN HEMT usually cause strong self-heating effects related to power dissipation problems. This problem can be overcome by using SiC substrate. In the final chapter, the HEMTs using SiC substrate and Si substrate were compared, and the HEMTs using SiC substrate show the better performance. In the HEMT with gate width of 1.2 mm, the maximum PAE is 38.4% and output power is 981 mW.

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