Optimization stability of gate dielectrics on gallium nitride

The application of gallium nitride (GaN)-based devices requires the use of a gate dielectric to reduce gate leakage, passivate surface traps, and provide isolation between devices. It is critical for the insulator to remain chemically and thermally stable at high temperatures (i.e., 1000°C) during device fabrication and operation. More importantly, it must possess good electrical characteristics such as a high breakdown field, low flatband voltage shift, and low interface trapped charge (Dit). A new dielectric material, known as scandium gallium oxide ((Sc2O3)x(Ga 2O3)1-x), was investigated. Growth conditions of MgxScyOz and MgO were also optimized to enhance their environmental stability and improve their electrical results.; All dielectric films were deposited by molecular beam epitaxy (MBE), which uses independent sources to precisely control the film thickness and stoichiometry. Initial films on GaN were characterized by using a wide variety of techniques to determine the crystal structure, surface roughness, chemical composition, and film thickness. Electrical diodes were then fabricated for electrical testing such as current-voltage and capacitance-voltage measurements.; Continuous and digital growth techniques for (Sc2O3) x(Ga2O3)1-x revealed segregation of Ga at the surface. The segregation was eliminated by utilizing a growth technique in which the Ga shutter was closed for a set amount of time towards the end of the growth while the O and Sc shutters remained open. A poor breakdown field of 0.15 MV/cm was obtained due to the presence of free Ga metal in the film.; Growth of MgxScyOz at low oxygen pressures showed breakdown fields as high as 4 MV/cm and Dit values in the low 1011 ev-1cm-2 range, but flatband voltage shift values ranging from 3.83-5.30 V were also obtained. The large flatband voltage shifts were attributed to defects generated from the mixed Sc (+3) and Mg (+2) valences.; Optimization of MgO growth parameters at low oxygen pressures and low growth rates showed improved environmental stability and good electrical results on both u-GaN and p-GaN. The use of a new processing scheme in which the ohmic metal is deposited prior to MgO showed good feasibility as it displayed comparable electrical results to the old scheme involving MgO deposition prior to ohmic metallization.