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Low-temperature MOS-gated Hall measurements and gated diode capacitance-voltage (C-V) measurements are used for characterizing both trap density and Hall mobility on 4H-silicon carbide MOSFETs with gate oxides grown by sodium enhanced oxidation (SEO) and thermally grown in [N.sub.2]O. The temperature-dependent Hall mobility measurements have revealed that inversion layer mobility in both the SEO and baseline samples are limited by Coulomb scattering from interface trapped charge and surface roughness.

The main scattering mechanisms limiting mobility in SiC MOSFETs were examined with the help of Hall-effect mechanisms of n-channel MOS devices. Findings reveal that surface-roughness scattering and Coulomb scattering were the main scattering mechanisms limiting electron mobility found in SiC MOSFETs at room temperature.

Research involving high-field effects in GaN MODFETs is described.

Research involving s low transients observed in AlGaN/GaN HFETs that are subjected to high bias stress is described and discussed.

The fabrication of high electron mobility transistors using undoped AlGaN/GaN structures and the induction of a two-dimensional electron gas are described.

Very slow drain current and surface potential transients have been observed in AlGaN/GaN heterostructure field effect transistors that are subjected to high bias stress. Simultaneous measurements of drain current and surface potential indicate that large change in surface potential after stress is responsible for the reduction in drain current in these devices. Measurements of surface potential profile from the gate edge toward the drain as a function of time indicate that surface potential changes occur mostly near the gate. It is proposed that the surface potential changes are caused by electrons which tunnel from the gate under high bias stress and get trapped at the surface states near the gate. Passivation of the surface with SiN[sub ℵ] reduces the transient magnitudes to a large extent. This correlates with a large improvement in microwave power performance in these devices after passivation. UV illumination of these devices totally eliminates the drain current and surface potential transients. [ABSTRACT FROM AUTHOR]