Yukako Kato

1 Ω On-Resistance Diamond Vertical-Schottky Barrier Diode Operated at 250 °C

Vertical-structured diamond Schottky barrier diodes with a thick field plate have been developed. The diamond VSBD with a 30 µm square (8.8×10-6 cm2) Schottky electrode shows specific on-resistance and blocking voltage, such as 29.3 mΩ cm2 (3.3 kΩ) and 842 V at room temperature, respectively, however, the lower specific on-resistance with a constant blocking voltage such as 9.4 mΩ cm2 (1 kΩ) and 840 V, respectively, have been realized at 250 °C. As a result, Baligas figure of merit (BVBD2/RonS) is improved from 24.1 to 75.3 MW/cm2. This value is the best in diamond diodes at present. The diamond VSBD with a 1,000 µm square (9.7×10-3 cm2) Schottky electrode shows high forward current and low on-resistance, such as more than 5 A and 10.2 mΩ cm2 (1.04 Ω), respectively, at 250 °C. The estimated parasitic resistance of the SBD is less than 0.04 Ω.

A 2-in. mosaic wafer made of a single-crystal diamond

We synthesized a mosaic diamond wafer 2 in. in size (40 × 60 mm2), which consisted of 24 single-crystal diamond (SCD) plates 10 × 10 mm2 in area, by using microwave plasma chemical vapor deposition. Even by using a cloning technique, cracking frequently occurred and the non-uniformity was remarkable for wafers that were larger than 1 in. in size. This has not been observed in smaller samples before. Appropriate crystallographic directions could avoid the cracking and is one of the predominant factors in fabricating large area SCD wafers. Comparison with numerical simulations highlighted the importance of uniformity of the substrate temperature distribution on the uniformity of the growth.

Significant increase in conduction band discontinuity due to solid phase epitaxy of Al2O3 gate insulator films on GaN semiconductor

We have investigated band discontinuities and chemical structures of Al2O3 gate insulator films on n-type GaN semiconductor by photoemission and x-ray absorption spectroscopy. It is found that the solid phase epitaxy at the GaN crystal during annealing procedures at 800 °C leads to phase transformation of Al2O3 films from amorphous to crystalline. Changes in crystallographic structures closely correlate with the significant increase in conduction band discontinuity at the Al2O3/GaN interface, which suggests that epitaxial Al2O3 films on GaN semiconductor, free from grain boundaries of Al2O3 polycrystalline, hold the potential for high insulation performance.

Site-Specific Orbital Angular Momentum Analysis of Graphite Valence Electron Using Photoelectron Forward Focusing Peaks

Two-dimensional photoelectron intensity angular distributions of the graphite valence band were measured using circularly polarized soft X-ray with a photon energy of 500 eV. Photoelectron intensit...

Effect of an Ultraflat Substrate on the Epitaxial Growth of Chemical-Vapor-Deposited Diamond

The performance of diamond power devices depends on the crystalline quality of the drift layer and conduction layer. Because the layers of diamond power device are usually grown by chemical vapor deposition, critical factors determining crystalline quality during this process should be discussed. An important related issue is the reduction of the density of dislocations in the epitaxial layer: the density of dislocations increases during chemical vapor deposition. We show that by using an ultraflat substrate, while existing dislocations in the epitaxial layer remained, no new dislocations were formed.

Electron correlation in the FeSe superconductor studied by bulk-sensitive photoemission spectroscopy

We have investigated the electronic structures of recently discovered superconductor FeSe by soft-x-ray and hard-x-ray photoemission spectroscopy with high bulk sensitivity. The large Fe 3d spectral weight is located in the vicinity of the Fermi level (EF), which is demonstrated to be a coherent quasi-particle peak. Compared with the results of the band structure calculation with local-density approximation, Fe 3d band narrowing and the energy shift of the band toward EF are found, suggesting an importance of the electron correlation effect in FeSe. The self energy correction provides the larger mass enhancement value (Z^-1=3.6) than in Fe-As superconductors and enables us to separate a incoherent part from the spectrum. These features are quite consistent with the results of recent dynamical mean-field calculations, in which the incoherent part is attributed to the lower Hubbard band.

A nitrogen doped low-dislocation density free-standing single crystal diamond plate fabricated by a lift-off process

A nitrogen-doped single crystal diamond plate with a low dislocation density is fabricated by chemical vapor deposition (CVD) from a high pressure high temperature synthetic type IIa seed substrate by ion implantation and lift-off processes. To avoid sub-surface damage, the seed surface was subjected to deep ion beam etching. In addition, we introduced a nitrogen flow during the CVD step to grow low-strain diamond at a relatively high growth rate. This resulted in a plate with low birefringence and a dislocation density as low as 400 cm−2, which is the lowest reported value for a lift-off plate. Reproducing this lift-off process may allow mass-production of single crystal CVD diamond plates with low dislocation density and consistent quality.

Evolution of magnetism in Yb(Rh1-xCox)2Si2

We present a study of the evolution of magnetism from the quantum critical system YbRh

X-ray Topography Used to Observe Dislocations in Epitaxially Grown Diamond Film

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Negative Photoelectron Diffraction Replica in Secondary Electron Angular Distribution

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