The correlation between atomic structure and the electrical properties of thermally grown SiO2/4H-SiC(0001) interfaces was investigated by synchrotron x-ray photoelectron spectroscopy together with electrical measurements of SiC-MOS capacitors. We found that the oxide interface was dominated by Si-O bonds and that there existed no distinct C-rich layer beneath the SiC substrate despite literature. In contrast, intermediate oxide states in Si core-level spectra attributable to atomic scale roughness and imperfection just at the oxide interface increased as thermal oxidation progressed. Electrical characterization of corresponding SiC-MOS capacitors also indicated an accumulation of both negative fixed charges and interface defects, which correlates well with the structural change in the oxide interface and provides insight into the electrical degradation of thermally grown SiC-MOS devices.

Improvement in electrical properties of thermally grown GeO2/Ge metal-oxide-semiconductor (MOS) capacitors, such as significantly reduced flatband voltage (VFB) shift, small hysteresis, and minimized minority carrier response in capacitance-voltage (C-V) characteristics, has been demonstrated by in situ low temperature vacuum annealing prior to gate electrode deposition. Thermal desorption analysis has revealed that not only water but also hydrocarbons are easily infiltrated into GeO2 layers during air exposure and desorbed at around 300 °C, indicating that organic molecules within GeO2/Ge MOS structures are possible origins of electrical defects. The inversion capacitance, indicative of minority carrier generation, increases with air exposure time for Au/GeO2/Ge MOS capacitors, while maintaining an interface state density (Dit) of about a few 1011 cm−2 eV−1. Unusual increase in inversion capacitance was found to be suppressed by Al2O3 capping (Au/Al2O3/GeO2/Ge structures). This suggests that electrical defects induced outside the Au electrode by infiltrated molecules may enhance the minority carrier generation, and thus acting as a minority carrier source just like MOS field-effect transistors.

The main components of a new beamline for surface and interface crystal structure determination at SPring-8 are briefly described. Stages for the beamline monochromator are modified for making an incident X-ray intensity more stable for surface X-ray experiments. Absolute photon flux densities were measured with an incident photon energy. A new ultrahigh vacuum system is introduced with preliminary X-ray measurements from an ordered oxygen on Pt (111) surface.

Initial oxidation of gallium nitride (GaN) (0001) epilayers and subsequent growth of thermal oxides in dry oxygen ambient were investigated by means of x-ray photoelectron spectroscopy, spectroscopic ellipsometry, atomic force microscopy, and x-ray diffraction measurements. It was found that initial oxide formation tends to saturate at temperatures below 800 °C, whereas the selective growth of small oxide grains proceeds at dislocations in the epilayers, followed by noticeable grain growth, leading to a rough surface morphology at higher oxidation temperatures. This indicates that oxide growth and its morphology are crucially dependent on the defect density in the GaN epilayers. Structural characterizations also reveal that polycrystalline α- and β-phase Ga2O3 grains in an epitaxial relation with the GaN substrate are formed from the initial stage of the oxide growth. We propose a comprehensive model for GaN oxidation mediated by nitrogen removal and mass transport and discuss the model on the basis of experimental findings.

A simple and feasible method for fabricating high-quality and highly reliable GaN-based metal-oxide-semiconductor (MOS) devices was developed. The direct chemical vapor deposition of SiO 2 films on GaN substrates forming Ga-oxide interlayers was carried out to fabricate SiO 2 / GaO x /GaN stacked structures. Although well-behaved hysteresis-free GaN-MOS capacitors with extremely low interface state densities below 10 10 cm %2 eV %1 were obtained by postdeposition annealing, Ga diffusion into overlying SiO 2 layers severely degraded the dielectric breakdown characteristics. However, this problem was found to be solved by rapid thermal processing, leading to the superior performance of the GaN-MOS devices in terms of interface quality, insulating property, and gate dielectric reliability.