The impact of in situ low-power N 2 plasma pretreatment, prior to silicon-nitride (SiN) deposition, was investigated in AlGaN/GaN high-electron mobility transistors (HEMTs). These studies reveal that the use of N 2 plasma in HEMT passivation reduces current-collapse and gate-lag effects. Such treatment is also beneficial to improve gate leakage, and from RF measurements, no degradation of f max was observed. These beneficial effects of the N 2 plasma pretreatment seem to be due to a significant reduction in interface charge density, as shown in this letter using GaN MIS devices, where a decrease of 60% was observed.

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A voltage tunable surface acoustic wave (SAW) phase shifter on a two-dimensional electron gas (2DEG) AlGaN/GaN heterostructure has been developed. The acoustoelectric interaction is field-effect modulated by means of an insulated gate placed in the acoustic path of a SAW delay line. The phase velocity under the gate is tuned by modifying the conductance of the 2DEG with a dc bias, while the insulating layer prevents the screening of the SAW piezoelectric fields by the gate. The device is compatible with the nitride transistor technology for signal processing and frequency control applications.

High electron mobility transistors (HEMTs) based on the AlGaN/GaN heterostructure were fabricated with treatments of either CF4 plasma or 19F+ implantation prior to gate deposition. The post‐treatment threshold voltage VT was shifted positively from ‐4.06 V to 0.25 V and ‐0.34 V, respectively. Subsequent 400 °C, up to 10 min furnace annealing increased the transconductance gm in both samples, leading to a two order of magnitude increase in drain current density. The implanted sample improved its VT to ‐0.16 V, whereas the VT of the CF4 plasma‐treated one reverted to ‐1.95 V. Annealing a commercial power HEMT (EPC1012, Efficient Power Conversion Corp.) under identical conditions resulted in stable VT within 1.4% (VT,Rated = 1.4 V). As the ambient temperature was increased to 150 °C, VT of our samples remained within 10% of the room‐temperature values. Reliability stress measurements were performed by applying a VSTRESS of ±1 V or ±2 V for up to 10 minutes. VT of EPC HEMTs increased with temperature and stress polarity, but remained close to specification up to the maximum rated temperature (125 °C) (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)