H. Itoh

Bio: H. Itoh is an academic researcher from University of Erlangen-Nuremberg. The author has contributed to research in topics: Medicine & Vacancy defect. The author has an hindex of 2, co-authored 3 publications receiving 267 citations.

Doping of SiC by Implantation of Boron and Aluminum

Abstract: Experimental studies on aluminum (Al) and boron (B) implantation in 4H/6H SiC are reported; the implantation is conducted at room temperature or elevated temperatures (500 to 700 C). Both Al and B act as ``shallow`` acceptors in SiC. The ionization energy of these acceptors, the hole mobility and the compensation in the implanted layers are obtained from Hall effect investigations. The degree of electrical activity of implanted Al/B atoms is determined as a function of the annealing temperature. Energetically deep centers introduced by the Al{sup +}/B{sup +} implantation are investigated. The redistribution of implanted Al/B atoms subsequent to anneals and extended lattice defects are monitored. The generation of the B-related D-center is studied by coimplantation of Si/B and C/B, respectively. (orig.) 60 refs.

Vacancy Defects Detected by Positron Annihilation

Abstract: Point defects in SiC is important in connection with the technological concerns such as ion implantation, crystal growth and radiation tolerance. Among different types of point defects, vacancy defects have been frequently argued in the past studies on irradiated SiC using deep level transient spectroscopy (DLTS), electron spin resonance (ESR), photoluminescence (PL), etc. Although these conventional approaches have a capability to discriminate different defect species, even indirect for the determination of the type of defects. Consequently, the origins of important energy levels in SiC have not yet been fully understood.

In Situ PD-L1 Expression in Oral Squamous Cell Carcinoma Is Induced by Heterogeneous Mechanisms among Patients

Abstract: The expression of programmed death ligand-1 (PD-L1) is controlled by complex mechanisms. The elucidation of the molecular mechanisms of PD-L1 expression is important for the exploration of new insights into PD-1 blockade therapy. Detailed mechanisms of the in situ expression of PD-L1 in tissues of oral squamous cell carcinomas (OSCCs) have not yet been clarified. We examined the mechanisms of PD-L1 expression focusing on the phosphorylation of downstream molecules of epidermal growth factor (EGF) and interferon gamma (IFN-γ) signaling in vitro and in vivo by immunoblotting and multi-fluorescence immunohistochemistry (MF-IHC), respectively. The in vitro experiments demonstrated that PD-L1 expression in OSCC cell lines is upregulated by EGF via the EGF receptor (EGFR)/PI3K/AKT pathway, the EGFR/STAT1 pathway, and the EGFR/MEK/ERK pathway, and by IFN-γ via the JAK2/STAT1 pathway. MF-IHC demonstrated that STAT1 and EGFR phosphorylation was frequently shown in PD-L1-positive cases and STAT1 phosphorylation was correlated with lymphocyte infiltration and EGFR phosphorylation. Moreover, the phosphorylation pattern of the related molecules in PD-L1-positive cells differed among the cases investigated. These findings indicate that PD-L1 expression mechanisms differ depending on the tissue environment and suggest that the examination of the tissue environment and molecular alterations of cancer cells affecting PD-L1 expression make it necessary for each patient to choose the appropriate combination drugs for PD-1 blockade cancer treatment.

Establishment of Mucoepidermoid Carcinoma Cell Lines from Surgical and Recurrence Biopsy Specimens

Abstract: Patients with advanced/recurrent mucoepidermoid carcinoma (MEC) have a poor prognosis. This study aimed to establish and characterize human mucoepidermoid carcinoma cell lines from the initial surgical specimen and biopsy specimen upon recurrence from the same patient to provide a resource for MEC research. MEC specimens from the initial surgical procedure and biopsy upon recurrence were used to establish cell lines. The established cell lines were cytogenetically characterized using multi-color fluorescence in situ hybridization and detection, and the sequence of the CRTC1-MAML2 chimeric gene was determined. Furthermore, the susceptibility of head and neck mucoepidermoid carcinoma to standard treatment drugs such as cisplatin, 5-fluorouracil, and cetuximab was investigated. We successfully established unique MEC cell lines, AMU-MEC1, from an initial surgical specimen and AMU-MEC1-R1 and AMU-MEC1-R2 from the recurrent biopsy specimen in the same patient. These cell lines exhibited epithelial morphology and developed in vitro-like cobblestones. They shared eight chromosomal abnormalities, including der(19)ins(19;11)(p13;?), which resulted in a chimeric CRTC1-MAML2 gene, indicating the same origin of the cell lines. The susceptibility of all cell lines to cisplatin and 5-fluorouracil was low. Interestingly, EGFR dependency for cell growth decreased in AMU-MEC-R1 and AMU-MEC-R2 but was retained in AMU-MEC1. These cytogenetic and biochemical findings suggest that the established cell lines can be used to investigate the disease progression mechanisms and develop novel therapeutics for MEC.

Rapid Research Note Positron Annihilation Due to Silicon Vacancies in 3C and 6H SiC Epitaxial Layers Induced by 1 MeV Electron Irradiation

Abstract: (a)Martin-LutherUniversita¨t,Friedemann-Bach-Platz6,D-06108,Halle,Germany(b)JapanAtomicEnergyResearchInstitute,TakasakiEstablishment,Watanuki,1233,Takasaki,Gunma,370-1292,Japan(Received November 5, 2000; in revised form December 1, 2000;accepted December 8, 2000)Subject classification:61.72.Ji; 78.70.Bj; S6Positron annihilation spectroscopy is extensively used to study vacancy-type defects in semiconduc-tors [1]. To characterize defects in SiC by this technique, it is necessary to know annihilation param-eters for various kinds of vacancies, e.g., silicon and carbon vacancies, divacancies and so on. Thelifetime of positrons trapped at isolated silicon vacancies in 3C SiC was determined to be 190 pspreviously [2] from the direct comparison of annealing behavior of positron lifetime and electronspin resonance (ESR) T1 signal, which is related to isolated silicon vacancies [3, 4]. Although theDoppler broadening Sparameter is also reported for silicon vacancies in the previous studies [5,6], this should be further confirmed. In addition, Wparameter is important when identifying va-cancies by the Doppler broadening measurements [1]. We note that silicon vacancies are annealedin two stages at approximately 200 and 700

Material science and device physics in SiC technology for high-voltage power devices

Abstract: Power semiconductor devices are key components in power conversion systems. Silicon carbide (SiC) has received increasing attention as a wide-bandgap semiconductor suitable for high-voltage and low-loss power devices. Through recent progress in the crystal growth and process technology of SiC, the production of medium-voltage (600?1700 V) SiC Schottky barrier diodes (SBDs) and power metal?oxide?semiconductor field-effect transistors (MOSFETs) has started. However, basic understanding of the material properties, defect electronics, and the reliability of SiC devices is still poor. In this review paper, the features and present status of SiC power devices are briefly described. Then, several important aspects of the material science and device physics of SiC, such as impurity doping, extended and point defects, and the impact of such defects on device performance and reliability, are reviewed. Fundamental issues regarding SiC SBDs and power MOSFETs are also discussed.

A review on single photon sources in silicon carbide.

Abstract: This paper summarizes key findings in single-photon generation from deep level defects in silicon carbide (SiC) and highlights the significance of these individually addressable centers for emerging quantum applications. Single photon emission from various defect centers in both bulk and nanostructured SiC are discussed as well as their formation and possible integration into optical and electrical devices. The related measurement protocols, the building blocks of quantum communication and computation network architectures in solid state systems, are also summarized. This includes experimental methodologies developed for spin control of different paramagnetic defects, including the measurement of spin coherence times. Well established doping, and micro- and nanofabrication procedures for SiC may allow the quantum properties of paramagnetic defects to be electrically and mechanically controlled efficiently. The integration of single defects into SiC devices is crucial for applications in quantum technologies and we will review progress in this direction.

Technological Breakthroughs in Growth Control of Silicon Carbide for High Power Electronic Devices

Abstract: Technological breakthroughs in growth control of SiC are reviewed. Step-controlled epitaxy by using off-axis SiC {0001} substrates to grow high-quality epitaxial layer is explained in detail. The introduction of substrate off-angles brings step-flow growth, which easily makes polytype replication of SiC at rather low temperatures. Off-angle dependence, rate-determining processes, and temperature dependence of growth rate are discussed. Prediction, whether step-flow growth or two-dimensional nucleation does occur, is given as a function of off-angle, growth temperature, and growth rate. Optical and electrical properties of undoped epitaxial layers are characterized. Impurity doping during the growth is explained. Recent progresses in peripheral technologies for realization of power electronic devices, such as bulk growth, epitaxial growth, ion implantation, MOS interface, ohmic contacts, are introduced. Finally application to high-power electronic devices is briefly described.

Effects of wet oxidation/anneal on interface properties of thermally oxidized SiO/sub 2//SiC MOS system and MOSFET's

Abstract: Effects of wet atmosphere during oxidation and anneal on thermally oxidized p-type and n-type MOS interface properties were systematically investigated for both 4H- and 6H-SiC. Deep interface states and fixed oxide charges were mainly discussed. The wet atmosphere was effective to reduce a negative flatband shift caused by deep donor-type interface states in p-type SiC MOS capacitors. Negative fixed charges, however, appeared near the interface during wet reoxidation anneal. In n-type SIC MOS capacitors, the flatband shift indicated a positive value when using wet atmosphere. The relation between interface properties and characteristics of n-channel planar 6H-SiC metal-oxide-semiconductor field effect transistors (MOSFETs) was also investigated. There was little relation between the interface properties of p-type MOS capacitors and the channel mobility of MOSFETs. The threshold voltage of MOSFETs processed by wet reoxidation anneal was higher than that of without reoxidation anneal. A clear relation between the threshold voltage and the channel mobility was observed in MOSFETs fabricated on the same substrate.

Surface roughening in ion implanted 4H-silicon carbide

Abstract: Silicon carbide (SiC) devices have the potential to yield new components with functional capabilities that far exceed components based on silicon devices. Selective doping of SiC by ion implantation is an important fabrication technology that must be completely understood if SiC devices are to achieve their potential. One major problem with ion implantation into SiC is the surface roughening that results from annealing SiC at the high temperatures which are needed to activate implanted acceptor ions, boron or aluminum. This paper examines the causes and possible solutions to surface roughening of implanted and annealed 4H-SiC. Samples consisting of n-type epilayers (5 × 1015 cm−3, 4 µm thick) on 4H-SiC substrates were implanted with B or Al to a total dose of 4 × 1014 cm−2 or 2 × 1015 cm−2, respectively. Roughness measurements were made using atomic force microscopy. From the variation of root mean square (rms) roughness with annealing temperature, apparent activation energies for roughening following implantation with Al and B were 1.1 and 2.2 eV, respectively, when annealed in argon. Time-dependent activation and surface morphology analyses show a sublinear dependence of implant activation on time; activation percentages after a 5 min anneal following boron implantation are about a factor of two less than after a 40 min anneal. The rms surface roughness remained relatively constant with time for anneals in argon at 1750°C. Roughness values at this temperature were approximately 8.0 nm. Annealing experiments performed in different ambients demonstrated the benefits of using silane to maintain good surface morphology. Roughnesses were 1.0 nm (rms) when boron or aluminum implants were annealed in silane at 1700°C, but were about 8 and 11 nm for B and Al, respectively, when annealed in argon at the same temperature.