We have studied the oxidation of layered compound GaSe with no dangling bonds on the cleaved surface using XPS and AES techniques. At room temperature, the cleaved surface is not oxidized in an oxygen atmosphere. When subjected to Ar ion sputtering, the surface starts to exhibit the behavior of metallic Ga owing to dissipation of the first sublayer of Se in the primitive layer, Se–Ga–Ga–Se. The thin layer of metallic Ga thus exposed is easily oxidized. In the thermal oxidation of cleaved GaSe in air, the oxygen diffuses into the primitive layer and combines with Ga, severing the intralayer bonding between the Se and Ga atoms. At temperature higher than 450°C, the oxygen is also intercalated between the primitive layers from the sides perpendicular to the layers. No Se oxides are observed under any of the oxidation conditions.

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4H‐SiC bipolar junction transistors (BJTs) are one of the promising candidates for next‐generation power devices. 4H‐SiC BJTs have the advantages of low on‐resistance and high temperature capability. On the other hand, high common emitter current gain is required from a practical use point of view because BJTs are current‐controlled devices. In order to improve the current gain of 4H‐SiC BJTs, we have concentrated on suppressing surface recombination on the SiC surface, which is a critical limiting factor of the current gain and can be suppressed by reducing carrier density and/or trap density. We have proposed novel 4H‐SiC bipolar junction transistors with suppressed surface‐recombination structure: SSR‐BJTs that have the SiC surface with low carrier density, characterized by a lightly doped n‐type layer (LDN layer) and a highly resistive p‐type region (HRP region). In addition, surface passivation suitable for reducing surface traps has been investigated by applying a new characterization method of surface‐recombination current in which the sp · Ls value, a product of a surface‐recombination velocity (sp) and a surface‐diffusion length (Ls), is derived from an analysis of forward I–V characteristics of SiC pn diodes. We have experimentally demonstrated that the sp · Ls value is a practical indicator to evaluate surface passivation. By using the characterization, an effective passivation method with the combination of a pyrogenic oxidation, a post‐oxidation anneal in H2 ambient, and an anneal in NH3 ambient has been developed. SSR‐BJTs with a variety of device structures and process conditions have been fabricated to investigate their characteristics. A fabricated SSR‐BJT showed a recorded maximum current gain of 134 at room temperature with a specific on‐resistance of 3.2 mΩ cm2 and a blocking voltage VCEO of 950 V. The SSR‐BJT kept a current gain of 60 °C at 250 °C with a specific on‐resistance of 8 mΩ cm2. These results have demonstrated the outstanding current‐gain capability of the SSR‐BJTs compared to conventional BJTs. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Titanium was deposited on a single-silicon wafer and made to form TiS2 by thermal annealing in vacuum. Samples were then oxidized at temperatures from 100 to 1000°C for 60 min in air. When the oxidized TiS2 was studied by X-ray photoelectron spectroscopy (XPS) in conjunction with argon-ion sputtering, SiO2 was found to be dominant in the oxide products at various oxidation temperatures. Full-width at half maximum (FWHM) and Si/Ti atomic ratio analyses led to the conclusion that various Ti oxides exist in oxidized TiSi2, but that the intermediate Ti-silicides (TiSi and Ti5Si3) do not. The growth of a Ti-free layer of SiO2 at 1000°C was also observed. SEM micrographs showed that no surface morphologies varied before or after oxidation in air at temperatures from 100 to 800°C. Above 1000°C, however, the TiSi2 film was thermally grooved at its grain boundaries, and the grain sizes were increased. Analytic electron-microscope photographs showed that the crystalline grains consisted of TiSi2, but that the grain boundaries lay within the Ti-free zone.