Oxidation by the UV & ozone process, nitridation by the nitrogen helicon-wave-excited plasma process, and the combination of these processes are applied to (100) GaAs wafers. An atomic force microscope, X-ray photoelectron spectroscopy, a transmission electron microscope, photoluminescence and electrical characteristics (current-voltage and capacitance-voltage) were used to analyze the influences of these processes on the structure and composition of the surfaces and the interfaces. Metal-insulator-semiconductor (MIS) diodes and Schottky diodes were fabricated in order to investigate the electrical influences of these processes. The oxidation slightly disorders GaAs surfaces. Nitridation of a bare surface creates about a 2nm-thick strongly disordered layer, which strongly deteriorates the electrical and photoluminescence characteristics. Nitridation of oxidated wafers (oxi-nitridation) forms firm amorphous GaON layers, which contain GaN, with very flat and sharp GaON/GaAs interfaces, where crystal disorder is hardly observed. It improves the current-voltage (I-V) and capacitance-voltage (C-V) characteristics and the photoluminescence intensity. Results of the structural and the electrical characterizations qualitatively coincide well with each other.

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We fabricated n-channel enhancementhnversion mode GaAs-MISFETs with nm-thin gate insulator, which is formed by oxidizing and nitriding GaAs surface. They have sharper pinch-off than GaAs-MOSFETs. Hysteresis is hardly observed. They showed transconductances of 50 m S / m (Vth -0 V) or 20 mSlmm (Vth 1V) depending on recess-etching time. They are 10 -100 times higher than those of previously reported devices.

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SUMMARYTest fabrication of n-channel p-channel enhancement/inversion mode GaAs-MISFET with a GaAs oxy-nitrided gate insulation film formed by nitriding after oxidation of the GaAs surface was performed. In comparison with MOSFET with only oxidation, the pinch-off and hysteresis characteristics are improved in MISFET. The confirmed values of the transconductance are 62 mS/mm (V th ~ 0 V), 41 mS/mm (V th ~ 1 V), and 14 mS/mm [V th = V flat (= 1.1 V)] for the n-channel type. These values are 10 to 100 times those reported previously in GaAs-MOSFET. The result realized for the p-channel type MISFET is about 9 mS/mm.