Threshold Voltage Instability in Al2O3/GaN/AlGaN/GaN Metal–Insulator–Semiconductor High-Electron Mobility Transistors

Abstract

The threshold voltage (Vth) instability in GaN-based metal–insulator–semiconductor high-electron mobility transistors (MIS-HEMTs) with 15-nm atomic-layer-deposited (ALD) Al2O3 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. Both Al2O3/GaN/AlGaN/GaN MIS diode and GaN/AlGaN/GaN Schottky diode only exhibit tiny threshold-voltage hysteresis (ΔVth) (<10 mV) in double-mode (up and down sweep) HFCV characteristics as the maximum forward bias (VFmax) during the sweep is set to 0 V, while an apparent ΔVth (as large as 0.9 V) emerges as VFmax is increased to +5 V for the MIS diode. The stability of Vth in the corresponding MIS-HEMTs is thus studied by increasing the maximum VGS (VGSmax) in the measurement of transfer characteristics. Significant positive Vth shift occurred once the VGSmax exceeds +1 V, while such Vth-instability is still absent in Schottky-gate 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. As the filling and emission processes of these interface states are slow, they are successfully captured by low-frequency QSCV techniques.