This study investigates a strong negative threshold voltage (V TH) shift observed in short-channel RF GaN MIS-HEMTs caused by hole generation under high drain bias in the OFF-state. The VTH instability problem results in an abnormally large drain induced barrier lowering (DIBL) effect in DC measurement. We quantitatively distinguish two groups of holes that cause a negative VTH shift of RF GaN MIS-HEMT under high drain: we demonstrate that holes can not only get trapped by MIS-HEMT gate defects but also accumulate as free holes near the MIS-HEMT gate region under the large VDG stress. The results reveal that, beyond DIBL and hole trapping, accumulated free holes in the gate region also contribute significantly to the negative VTH shift under high drain bias.
