| Summary: | 碩士 === 國立中央大學 === 電機工程學系 === 105 === 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.
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