Characterization of Vth-instability in Al2O3/GaN/AlGaN/GaN MIS-HEMTs by quasi-static C-V measurement



The threshold-voltage (Vth) instability in AlGaN/GaN MIS-HEMTs with ALD-Al2O3 (15 nm) as gate dielectrics is systematically investigated by dc current-voltage (I-V), high-frequency capacitance-voltage (C-V) (HFCV), and quasi-static C-V (QSCV) characterizations. For Al2O3/GaN/AlGaN/GaN MIS diodes, tiny Vth hysteresis (ΔVth) appears in double-mode (up and down sweep) HFCV measurements if the maximum forward bias (VF,max) is only set to 0 V, while an apparent clockwise ΔVth (as large as 0.9 V) emerges as VF,max is increased to +5 V. The stability of Vth in the corresponding MIS-HEMTs is thus studied by increasing the maximum VGS (VGS,max) in the measurement of double-mode transfer characteristics. Significant clockwise ΔVth also occurred once the VGS,max exceeds +1.1 V, and it increased to ∼1 V at VGS,max= +3 V. Such Vth-instability is absent in AlGaN/GaN HEMTs. It is suggested that the acceptor-like deep states at Al2O3/GaN interface account for the Vth-instability in Al2O3/GaN/AlGaN/GaN MIS-HEMTs, and their filling and emission processes are successfully captured by QSCV measurements. The interface state density detected is about 4.6×1012 cm-2 using 1 Hz QSCV. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)