本論文中，為了解決在氮化鎵有關之異質接面電晶體中，蕭基介面以及歐米介面不能同時兩全的問題，我們利用了光激發濕式蝕刻的高選擇性，做出閘極下凹式的異質接面電晶體，發現經過閘極下凹的處理，蕭基特性中的漏電流由原本的3x10-2 mA/mm縮小至 7.49x10-3 mA/mm，電晶體特性中的漏電流也從8.06 mA/mm 縮小至 7.17 mA/mm，轉導值也從原本的 47 mS/mm 增加至 52.09 mS/mm。但是在氮化銦鎵作為通道層的結構中，電晶體特性並沒有預期中的增加，因此，在新結構中，我們在氮化鋁鎵及氮化銦鎵之間，插入一層氮化鎵作為緩衝層。為了取得更好的歐米特性，在原本的結構上，增加了重摻雜的氮化鎵層，再利用光激發濕式蝕刻來做閘極下凹的處理，其蕭基特性漏電流低至5.6x10-5 mA. 電晶體特性中，漏電流壓低至1.95 mA/mm，轉導值也為三種結構中最高的 94.82 mS/mm

　In this thesis, in order to solve the problem of trading off the ohmic-contact and schottky performance in GaN based heterojunction field effect transistor, Photo-enhanced chemical wet etching method is incorporated into the recessed gate process owing to its good etching selectivity. As the results would demonstrated, the recessed gate process did significantly improve the schottky performance of device. The leakage current decreased from 8.06 mA/mm to 7.17 mA/mm. The Gm peak value increased from 47 mS/mm to 52.09 mS/mm. However, the characteristics of the InGaN channel layer were not as good as what we had anticipated. In order to improve the quality of AlGaN/InGaN layer, the GaN buffer layer was inserted between AlGaN and InGaN layer. The entire structure was capped by an n+-GaN layer to achieve better ohmic characteristics. Using the recessed gate process has successfully brought down the leakage current and its density of Schottky contact to 5.6x10-5 mA and 1.95 mA/mm respectively, while the Gm peak value is increased to 94.82 mS/mm which is the highest among AlGaN/GaN, AlGaN/InGaN/GaN and recessed gate sturcture.

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