利用氮化鎵取代傳統矽材料製作功率元件，可以大幅降低元件切換時的能量損耗，而製作增強型氮化鎵場效電晶體，是目前氮化鎵功率場效電晶體的趨勢。在此研究中我們設計一新穎的常關型氮化鎵金絕半場效電晶體，利用氮化鋁銦(AlInN)及氮化鋁鎵(AlGaN)形成雙通道結構，搭配閘極掘入蝕刻與原子層沉積(Atomic Layer Deposition, ALD)之氧化鋁(Al2O3)，實現常關型、低導通電阻、高導通電流之特性。我們利用一維Poisson 能帶模擬軟體來設計增強型場效電晶體結構，並使用有機金屬磊晶法成長此結構，在LSD為28 um，Lg為3 um的元件上實現之常開型AlInN 蕭基閘極電晶體，其臨界電壓為-5.2 V、操作電流達260 mA/mm，崩潰電壓高達1,030 V，且漏電流為0.4 mA；而常關型AlInN金絕半電晶體在同樣的元件尺寸下，其臨界電壓可高達3 V、操作電流達到175 mA/mm、閘極偏壓10 V時漏電流在10-6 A/mm等級，同時20 nm 厚的Al2O3閘極可承受電壓達正負13 V。研究結果顯示此常關型功率元件具有相當高的應用潛力。GaN-based power devices are under intensive investigations to replace their silicon counterparts for low switching loss. Currently, the development of normally-off GaN field-effect transistors (FETs) is the mainstream of this research area. In this study, we successfully demonstrate normally-off, low on-resistance and high drain current characteristics by using a novel AlInN/AlGaN double channel structure with recessed gate and atomic layer deposition (ALD) Al2O3 process technology.1D Poisson simulation on band diagram is used to design the novel FET structure. Metal organic chemical vapor deposition (MOCVD) is used to grow the AlInN/GaN/AlGaN/GaN double channel structure on sapphire substrate with an AlN-based buffer layer. For normally-on Schottky gate AlInN FETs with LDS/LG/WG of 28/ 3/ 200 um, Vth of -5.2 V, drain current density of 260 mA/mm, and record-high breakdown voltage up to 1,030 V with leakage current of 0.4 mA are achieved. In contrast, the normally-off MISFETs exhibit threshold voltage as high as 3 V with drain current density of 175 mA/mm at gate bias of 10 V. With a 20 nm-thick Al2O3 gate, the gate leakage current density is reduced to 10-6 A/mm under bias up to 12 V. The results of this work show that these normally-on and normally-off FETs have high potential for future power electronics.
