本論文係針對一增強型(E-mode)高功率氮化鎵異質場效電晶體，探討其動態特性與電荷陷捕行為之關係。過去之文獻報導，氮化鎵異質場效電晶體之動態電阻會隨著截止狀態(off-state)之汲極偏壓增加而增加，反映出越嚴重的陷捕效應。但是隨著更多元之磊晶結構與製程的出現，有些氮化鎵元件卻有大為不同的特性，也就是元件經歷高汲極偏壓後，其動態電阻反而會小於截止前之電阻，亦即動態電阻比值小於1。 為此，本研究針對此類元件之動態電容(∆Cds)進行測量分析，以了解其與動態電阻之關聯。此元件之動態電容顯示，元件在低截止偏壓(200 V)時，電子被陷捕(trapping)的情形明顯，而在高截止偏壓(600 V)時，則以脫阱(detrapping)行為為主。此脫阱行為發生後，會對元件產生長時間的影響，亦即約12小時才能夠恢復至初始狀態。根據變溫量測所得之活化能得知，與陷捕有關之陷阱(TP1)屬於初始不帶電子的陷阱(initially empty traps)，推估其陷阱能階在導電帶下方0.54 eV。而主要造成脫阱效應之陷阱(DP1, DP2)為初始狀態時就帶有電子的陷阱(initially occupied traps)，推估其陷阱能階分別為導電帶下方0.44 eV以及0.59 eV。造成脫阱效應之後，元件之導通電流隨即上升，然而隨著電子逐漸回填，導通電流也逐漸下降恢復平衡值。 ;In this work, the dynamic characteristics of an enhancement-mode (E-mode) high power GaN heterostructure field-effect transistor (HFET) are investigated to correlate with charge trapping in the device. It has been reported that the dynamic on-resistance of GaN-based FETs increases with the off-state drain voltage due to severe charge trapping in the devices. However, we have recently observed contrary behavior on devices fabricated in a commercial foundry. That is the dynamic on-resistance is actually smaller than the initial value after a higher off-state drain voltage stress. In his work, capacitance- voltage characteristics of the device after off-state stress are measured to obtain ∆Cds and correlated with its dynamic on-resistance. Based on these results, a model is proposed in which charge-trapping process occurs under low off-state stress whereas charge-detrapping effect becomes significant with increasing off-state stress. The detrapping process have a prolonged influence on the device; that is, it will not recover to the initial state within 12 hours. According to the activation energy obtained by the temperature-dependent drain current transient measurements, this study reveals that a trap dsigated as TP1, which is initially empty trap with an apparent trap energy level of 0.54 eV below the conduction band, is related to trapping effect. Others traps, i.e. DP1 and DP2, are initially occupied traps with an apparent trap energy level of 0.44 eV and 0.59 eV below the conduction band, respectively. Both of them are related to the detrapping effect. Due to the detrapping process, the on-current of the device is higher than that before off-state stress. As the electrons gradually refill the traps, the on current gradually decreases to restore the equilibrium value.
