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Ambient-pressure X-ray photoelectron spectroscopy is used to unveil the water uptake of a thin GeO2 film on Ge(100) as well as its effect on the electronic properties of the oxide film. We also compare these results with those for a SiO2/Si(100) sample. We detect significant positive charging of the GeO2 film once it is exposed to water vapor even at a low relative humidity (RH) of approximately 10-4%. We also show that the amount of adsorbed water is much larger on GeO2 than on SiO2 at RH above 10-4%, probably due to the permeability of GeO2. Two possible mechanisms are proposed to explain such water-induced positive charging of the GeO2 film.

High-quality germanium-on-insulator (GOI) and fully relaxed silicon germanium(SiGe)-on-insulator (SGOI) structures have been demonstrated by the rapid melt growth method. We successfully fabricated single-crystalline local GOI structures, that is, Ge wires over 100 um long within microcrucibles of a few um wide by means of lateral liquid phase epitaxy (lateral LPE). GOI MOSFETs produced by lateral LPE exhibited superior carrier mobility and on/off current ratio to those of conventional SOI devices, indicating excellent electrical properties of Ge-channel and MOS interface formed by LPE. Moreover, dislocation-free fully relaxed SiGe layers on SOI substrates were demonstrated by vertical LPE, in which crystallographic defects were found to be confined within the compositionally graded SiGe interlayer between the epitaxcially grown relaxed SiGe and SOI layers. These novel methods based on the rapid metal growth will open up a new pathway to realize platform for next-generation Ge-based high-mobility transistors and photonic devices.

Silicon carbide has gained considerable attention for future power electronics. However, it's well known that SiC-based MOS devices have suffered from degraded electrical properties of thermally grown SiO2/SiC interfaces, such as low inversion carrier mobility and deteriorated gate oxide reliability. This paper overviews the fundamental aspects of SiC-MOS devices and indicates intrinsic obstacles connected with an accumulation of both negative fixed charges and interface defects and with a small conduction band offset of the SiO2/SiC interface which leading to the increased gate leakage current of MOS devices. To overcome these problems, we proposed using aluminum oxynitride (AlON) insulators stacked on thin SiO2 underlayers for SiC-MOS devices. Superior flatband voltage stability of AlON/SiO2/SiC gate stacks was achieved by optimizing the thickness of the underlayer and nitrogen concentration in the high-k dielectrics. Moreover, we demonstrated reduced gate leakage current and improved current drivability of SiC-MOSFETs with AlON/SiO2 gate stacks.

We have proposed a new approach for controlling both gate metal effective work functions and interface layer thickness at the same time based on the incorporation of hetero atoms into HfO2 gate dielectrics. We investigated C atom incorporation into HfO2 by the first principles calculations. The results indicate that additional C atoms in HfO2 can reduce an interfacial SiO2 layer, which also causes modification of a gate metal effective work function. Redesigning interface thermodynamics by incorporating hetero atoms can be a crucial recipe for controlling both gate metal work functions and thickness of interfacial SiO2 layers in high-k gate stacks

Thermal stability and the electron irradiation damage to the ordered structure in the thermal oxide on Si substrates are shown, together with the fundamentals of the quasi-amorphous structural model. The mechanism and rate enhancement of SiGe oxidation is also discussed based on the ordered structure in the oxide layer.

Instability of the effective work function (WF) of metal/Hf-based high-k gate stacks was investigated by means of the flat-band voltage (Vfb) shift in capacitance-voltage curves and interface dipole characterized by x-ray photoelectron spectroscopy. We observed a negative Vfb shift and corresponding interface dipole, which suggest formation of oxygen vacancy (Vo) in the Hf-based oxides. In contrast, we observed an opposite (positive) Vfb shift and interface dipole when Au electrodes were formed on cleaned Hf-based dielectrics. This indicates that Au-Hf bond hybridization at the Au/HfSiON interface also causes effective WF modulation, as theoretically predicted by Shiraishi et al. Moreover, the interface dipole causing positive Vfb shift was found to be stable under vacuum and dry ambient, but it was gradually released when the gate stacks were exposed to the air and wet ambient.

We demonstrate two topics of the application of synchrotron X-ray diffraction methods to thin films used in gate stack structures. One is related to the structural change in the interfacial SiO2 layer between the high-k dielectric layer and the Si substrate. It is shown that O2 molecules dissociate into O atoms during diffusion through the HfO2 layer and these O atoms destroy the ordered SiO2 in the interfacial layer. The other is the characterization of strained Si wafers using a synchrotron X-ray microbeam diffraction and topography. The nonuniformity in micro- and centimeter scales is shown for the SiGe layer of the strained Si wafers.

Back-gate Ge-on-insulator metal–oxide–semiconductor field-effect transistors were fabricated using Ge wires grown by lateral liquid phase epitaxy. They exhibited a very high peak hole mobility of 511 cm2/Vs and an on/off current ratio of 106due to the superior crystalline quality of the Ge wires. The optical properties of the Ge wires were also investigated by micro-photoluminescence spectroscopy, and a direct band gap shrinkage of 45 meV was observed due to the introduction of 0.4% tensile strain.

We propose the use of an aluminum oxynitride (AlON) gate insulator for SiC-based MOS power devices. Although direct deposition of AlON on 4H-SiC substrate causes electrical degradation, the fabricated MOS capacitor with AlON/SiO2 stacked gate dielectric shows no flatband voltage (VFB) shift and negligible capacitance-voltage (C-V) hysteresis. Owing to the high dielectric constant of AlON, as compared to single SiO2 insulator, significant gate leakage reduction was achieved even at high-temperatures, especially in high electric field condition. Moreover, in order to improve electrical properties of thermally grown SiO2/SiC interfaces, the impact of a combination treatment of nitrogen plasma exposure and forming gas annealing (FGA) was investigated. We found that channel mobility enhancement of SiC-MOSFETs was consistent with the reduction in interface state density (Dit) depending on the process conditions of the combination treatment, and obtained 50% mobility enhancement, while maintaining low gate leakage current.

We have proposed a new approach for controlling both gate metal effective work functions and interface layer thickness at the same time based on the incorporation of hetero atoms into HfO2 gate dielectrics. We investigated C atom incorporation into HfO2 by the first principles calculations. The results indicate that additional C atoms in HfO2 can reduce an interfacial SiO2 layer, which also causes modification of a gate metal effective work function. Redesigning interface thermodynamics by incorporating hetero atoms can be a crucial recipe for controlling both gate metal work functions and thickness of interfacial SiO2 layers in high-k gate stacks