Characterization of VT-instability in enhancement-mode Al2O3-AlGaN/GaN MIS-HEMTs

The threshold voltage (V-T) instability of metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) is investigated. In the enhancement-mode AlGaN/GaN MIS-HEMT fabricated by fluorine plasma implantation technique featuring Al2O3 gate dielectric, a hysteresis of 0.6 V in transfer characteristics is observed by quasi-static I-V (current-voltage) measurement, in which the gate bias is swept at a low rate (0.7 V/s). Pulsed transfer characteristics measurement, however, unveils much larger hysteresis under the same gate voltage swing. The V-T-instability is attributed to the traps located at the dielectric/III-nitride interface as well as in the bulk of gate dielectric. It is proposed that pulsed measurement can count for the effect of fast traps (shallow traps) while the quasi-static measurement can only reflect slow traps (deep traps), and is more accurate for V-T-instability evaluation. In addition, the existence of bulk traps is implied by a slow time-dependent shift of V-T under large gate bias. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim