The adsorption of atomic hydrogen on a rutile TiO 2 (110) surface was investigated by nuclear reaction analysis (NRA), ultraviolet photoelectron spectroscopy (UPS), and conductivity measurements. The TiO 2 (110) surface was annealed in O 2 of 1 × 10 −4 Pa, which is regarded as a quasi-stoichiometric surface. After exposure to atomic hydrogen, UPS showed a localized in-gap state (IGS) at about 0.8 eV below the Fermi level and downward band bending with a decrease in the work function. Along with these changes, the conductivity was increased by 2.9 µS=□. Our results indicate that hydrogen donates electrons to the substrate. The amount of charge transfer and electric conductivity are discussed on the basis of the experimental data.

The effects of hydrogen exposure on the electronic structure of two types of SrTiO3(001) surfaces, oxygen-deficient (OD) and nearly-vacancy-free (NVF) surfaces, were investigated with ultraviolet photoemission spectroscopy and nuclear reaction analysis. Upon molecular hydrogen exposure to the OD surface which reveals in-gap states at 1.3 eV below the Fermi level, the in-gap state intensity was reduced to half the initial value at a hydrogen coverage of 0.9 ± 0.7 × 10(14) cm(-2). On the NVF surface which has no in-gap state, on the other hand, atomic-hydrogen exposure induced in-gap states, and the hydrogen saturation coverage was evaluated to be 3.1 ± 0.8 × 10(14) cm(-2). We argue that H is positively charged as H(∼0.3 +) on the NVF surface by being coordinated to the O atom, whereas H is negatively charged as H(-) on the OD surface by occupying the oxygen vacancy site. The stability of H(-) at the oxygen vacancy site is discussed.

The influence of electron irradiation and the subsequent oxygen adsorption on the electronic structure of an SrTiO3(001) surface was investigated by ultraviolet photoemission spectroscopy (UPS). Electron irradiation induced an in-gap state (IGS) as observed by UPS keeping the surface 1 × 1, which is considered to originate from oxygen vacancies on the topmost surface due to the electron-stimulated desorption (ESD) of oxygen. Electron irradiation also caused a downward shift of the valence band maximum, indicating downward band bending and the formation of a conductive layer on the surface. Adsorption of oxygen on the electron-irradiated surface, on the other hand, reduced the intensity of the IGS along with yielding upward band bending, which points to disappearance of the conductive layer. The results show that ESD and oxygen adsorption can be used to control the surface electronic structure switching between semiconducting and metallic regimes by changing the density of the oxygen vacancies.

The production of 150 mm-diameter SiC epi-wafers is the key to the spread of SiC power devices. Besides, step-bunching free surface leads to high-performance devices. We have developed the production technology of the epitaxial growth with smooth surface morphology for 4º off Si-face 4H-SiC epitaxial layers on 150 mm diameter substrates. The various area observations of the surface by optical surface analyzer, confocal microscope and atomic force microscope revealed that there was no conventional step-bunching in whole wafer surface. While creating step-bunching free surface is more difficult for thicker epilayer growth, we have achieved step-bunching free surface for 30-μm thick epilayer on a 150 mm diameter substrate. The typical values of thickness uniformity of the 30μm-thick epilayer are 0.5% (σ/mean) and 1.7% (range/mean). A few interfacial dislocations (IDs) were detected for the 150 mm-diameter epi-wafer by reflection X-ray topography. We have succeeded in removal of IDs by the optimized growth condition.

We have developed a single-wafer vertical epitaxial reactor which realizes high-throughput production of 4H-SiC epitaxial layer (epilayer) with a high growth rate [1,2]. In this paper, in order to evaluate the crystalline defects which can affect the characteristics of devices, we investigated the formation of variety of in-grown stacking faults (SFs) in detail. Synchrotron X-ray topography, photoluminescence (PL) and transmission electron microscopy are employed to analyze the SFs and the origins of the SF formation are discussed. The result in reducing in-grown SFs in fast epitaxial growth is also shown.