現今商用增強型(E-mode)高功率氮化鎵異質場效電晶體中，p型氮化鎵閘極是常用的閘極結構之一，此閘極對元件開關時的動態特性影響以及與可靠度的關聯性是必須要了解的重要研究課題。 本論文之研究內容是針對p型氮化鎵閘極高電子遷移率電晶體，測量元件在施加閘極應力過程與之後的特性，並分析其動態特性與電荷陷捕行為之關聯。 過去的文獻報導，氮化鎵高電子遷移率電晶體之閘極經過導通偏壓(on state)後，因載子陷捕效應，會造成元件發生臨界電壓偏移或是動態電阻上升等問題。本研究經由分析臨界電壓偏移在受閘極應力後隨著時間回復的行為，判斷這是由兩種載子遷移機制所導致。第一種為電子陷捕機制，其恢復時間常數較短；而另一種為電洞陷捕機制，其恢復時間常數較長。除了臨限電壓偏移的觀察以外，元件在高閘極偏壓(7V)後切換至關閉狀態時，汲極關閉電流會隨著閘極應力的時間而增加，這可能是有陷補電洞而誘導出更多通道電子所導致。根據電流暫態變化所萃取之活化能以及能帶模擬的結果推估，陷捕電子的陷補能階位置約莫在氮化鋁鎵位障層導電帶下方0.45 eV的位置，而陷捕電洞的陷捕能階約在p型氮化鎵或者氮化鋁鎵位障層價電帶上方0.54 eV的位置。 ;Normally off p-GaN gate AlGaN/GaN HEMTs have gained increasing popularity in power switching applications since their commercial availability. However, device reliability and stability reflected in dynamic characteristics are still of great concern. This work is aimed at analyzing the dynamic characteristics and charge trapping behavior of this p-GaN gate AlGaN/GaN HEMTs under the gate stress. The effects of on-state stresses on the dynamic behaviours of devices have been explored to correlate the device characteristics and the trapping behavior in the device. A significant change in Vth due to different on-state gate stresses is observed. ∆Vth transient analysis reveals two different mechanisms responsible for the change of Vth. On-state stress below 7V causes positive ∆Vth, indicating electron trapping with a shorter recovery time constant and hole trapping mechanism with a longer recovery time constant as observed by the negative shift in Vth after a 7V on-state stress. In addition to the change in Vth, the off-state Id increases with the on-state stress time at 7V. This is attributed to the presence of trapped holes, which induce excess electrons in the channel to maintain charge neutrality and hence the off state drain current. According to the activation energy obtained by the drain current transient measurements, an apparent electron trap energy level of 0.45 eV below the AlGaN barrier conduction band and a hole trap energy level of about 0.54 eV above the p-GaN or AlGaN valence band are estimated.
