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Now showing items 1 - 16 of 24

  • RF-MBE growth of InN on 4H-SiC (0001) with off-angles

    Orihara, Misao   Takizawa, Shin   Sato, Takanori   Ishida, Yuuki   Yoshida, Sadafumi   Hijikata, Yasuto   Yaguchi, Hiroyuki  

    We have grown InN on 4H-SiC (0001) substrates with various off-angles by RF-N-2 plasma molecular beam epitaxy (RF-MBE). Scanning electron microscope observation revealed that InN films grown on 4H-SiC (0001) substrates with off-angles of 4 degrees and 8 degrees are very smooth and that there are no voids which have often observed for InN epitaxial layers. X-ray diffraction reciprocal space maps for InN grown on 4H-SiC (0001) showed that the c-axes of InN grown on 4H-SiC 4 degrees and 8 degrees off substrates are inclined by 0.35 degrees and 0.8 degrees, respectively, toward the misorientation of the substrate while the c-axis of InN is parallel to that of 4H-SiC for the on-axis substrate. Strong PL peak was observed from InN grown on 4 degrees off substrate at 0.68 eV at 15 K. The PL peak was clearly observed even at room temperature and simply shifted to lower energies with increasing temperature. The difference in the PL peak energy between at 15 K and 300 K was 20 meV, which is reasonable taking into account the difference in the thermal coefficients of InN and SiC. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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  • Hopping conduction range of heavily Al-doped 4H-SiC thick epilayers grown by CVD

    Ji, Shiyang   Eto, Kazuma   Yoshida, Sadafumi   Kojima, Kazutoshi   Ishida, Yuuki   Saito, Shingo   Tsuchida, Hidekazu   Okumura, Hajime  

    To outline the hopping conduction range, the electrical characteristics of CVD-grown heavily Al-doped 4H-SiC thick epilayers (2.0 x 10(19)-4.0 x 10(20) cm(-3)) were investigated in a wide temperature regime (20-900 K). It is found that, below 100 K, hopping conduction dominates the carrier transport for all epilayers, and the corresponding hopping conduction activation energy shows a maximum of similar to 30 meV at around 1.1 x 10(20) cm(-3). With increasing doping level, the temperature dependence of resistivity evolves and finally obeys the similar to 1/T-1/4 law in the entire temperature regime, which gives direct evidence of variable-range hopping conduction. (C) 2015 The Japan Society of Applied Physics
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  • Filling 4H-SiC trench towards selective epitaxial growth by adding HCl to CVD process

    Ji, Shiyang   Kojima, Kazutoshi   Kosugi, Ryoji   Saito, Shingo   Sakuma, Yuuki   Tanaka, Yasunori   Yoshida, Sadafumi   Himi, Hiroaki   Okumura, Hajime  

    In this study, 4H-SiC stripe-shaped trenches preformed on an n(+) substrate were filled by adding HCl to the chemical vapor deposition process at relatively high pressures. HCl was found capable of counterbalancing the deposition on the mesa top by strong etching, and it thus enabled quasi-selective epitaxial growth across the whole extents of the trenches, where the epilayer preferentially grows from the trench bottom. Using the established technique, the 1-mu m-wide 4H-SiC trenches, with an aspect ratio of 5, which is the highest aspect ratio to date, were completely filled at a growth rate above 0.5 mu m/h and acquired a flat end surface. (C) 2015 The Japan Society of Applied Physics
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  • Dependence of conduction mechanisms in heavily Al-doped 4H-SiC epilayers on Al concentration

    Matsuura, Hideharu   Takeshita, Akinobu   Imamura, Tatsuya   Takano, Kota   Okuda, Kazuya   Hidaka, Atsuki   Ji, Shiyang   Eto, Kazuma   Kojima, Kazutoshi   Kato, Tomohisa   Yoshida, Sadafumi   Okumura, Hajime  

    To reduce the resistivity of heavily Al-doped 4H-SiC epilayers, the conduction mechanisms were investigated for Al concentrations (C-Al) between 2.4 x 10(19) and 4.7 x 10(29) cm(-3) and measurement temperatures (T) between 20 and 600K. The results elucidated the relationship between the conduction mechanisms and the values of Tand C. For the epilayers with C-Al similar to 3 x 10(19) cm(-3), an unexpected additional conduction mechanism was observed between the band and nearest-neighbor-hopping conduction regions, for which two plausible conduction models are proposed. To reduce the resistivity of epilayers with C-Al > 2 x 10(20) cm(-3), it is essential to fabricate samples with low lattice distortion. (C) 2018 The Japan Society of Applied Physics
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  • Effect of reduced pressure on 3C-SiC heteroepitaxial growth on Si by CVD

    Ishida, Yuuki   Takahashi, Tetsuo   Okumura, Hajime   Arai, Kazuo   Yoshida, Sadafumi  

    The difference between atmospheric pressure (AP)CVD and low pressure (LP)CVD in 3C-SiC heteroepitaxial growth on Si(001) surfaces has been investigated. It is found that the difference in the growth mode results in a difference in the secondary nucleation rate. It is suggested that the increase of the secondary nucleation rate causes 2D island growth on {111} faces, and that these 2D islands play an important role in the process of elimination of planar defects. A simulation of the homogeneous chemical reaction in the gas phase suggests that the origin of the difference in the secondary nucleation rate can be attributed to the difference in the mole fraction of atomic hydrogen.
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  • Suppressing Al memory effect on CVD growth of 4H-SiC epilayers by adding hydrogen chloride gas

    Ji, Shi-yang   Kojima, Kazutoshi   Ishida, Yuuki   Saito, Shingo   Yoshida, Sadafumi   Tsuchida, Hidekazu   Okumura, Hajime  

    The Al memory effect during the growth of Al-doped 4H-SiC by the hot-wall chemical vapor phase epitaxy method was investigated. To suppress unintentional incorporation of Al impurities during succeeding growth, a technique was developed by employing HCl-assisted "site-competition" growth. Three methods of introducing HCl, namely, HCl flushing before growth, HCl addition during growth, and the combination of the two preceding methods, have been performed and the Al suppression effects corresponding to the input C/Si ratio were studied separately. It is found that lowering the C/Si ratio reduces Al incorporation for all methods of introducing HCl and using the combination of HCl flushing and HCl addition is highly effective. Optimizing growth rate, temperature, and pressure can further improve Al suppression efficiency; thus, a highly abrupt change in Al distribution between Al-doped and undoped epilayers with Al concentration differences of more than five orders of magnitude was obtained, e.g., a steep change from 10(20) to 10(14)cm(-3). (C) 2014 The Japan Society of Applied Physics
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  • Investigation of giant step bunching in 4H-SiC homoepitaxial growth:Proposal of cluster effect model

    Ishida, Yuuki   Yoshida, Sadafumi  

    We have investigated the H-2 etching and growth conditions causing giant step bunching (GSB) in 4H-SiC homoepitaxial growth on 8 degrees off-axis substrates by a chemical vapor deposition method and found that GSB does not occur during H-2 etching under a wide range of experimental conditions, whereas GSB occurs during epitaxial growth at extremely low or high C/Si ratios, i.e., an excessive supply of SiH4 or C3H8. To explain these results, we have proposed a model taking into account the effect of Si or C cluster formation called "the cluster effect" model. We have shown that the cluster effect model can explain well our experimental result of GSB occurrence or nonoccurrence during etching and homoepitaxial growth of 4H-SiC. (C) 2015 The Japan Society of Applied Physics
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  • Suppression of Al Memory-Effect on Growing 4H-SiC Epilayers by Hot-Wall Chemical Vapor Deposition

    Ji, Shiyang   Kojima, Kazutoshi   Ishida, Yuuki   Yoshida, Sadafumi   Tsuchida, Hidekazu   Okumura, Hajime  

    Al memory-effect during the growth of p-type 4H-SiC by hot-wall chemical vapor deposition method was investigated. A technique of suppressing the unintentional Al impurities incorporating into succeeding growth was developed by utilizing "site-competition" growth technology. Lowering C/Si ratio from 1 to 0.4 effectively reduced the level of incorporated Al-impurity almost 3 orders, and a high abrupt Al distribution between Al-doped layer and undoped layer was obtained at a reduction factor about 1/17000 with Al-impurity concentration in the undoped layer decreased to the range of 10(15) cm(-3). In addition, it is found that, due to low C/Si ratio, the nitrogen impurity concentration increases about one order of magnitude up to the order of 10(16) cm(-3). Combining with site-competition growth technology, the influences of growth temperature and pressure on Al-impurity concentration were examined. (C) 2013 The Japan Society of Applied Physics
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  • Aspects and Prospects of the Researches on the Development of SiC Devices.

    YOSHIDA, Sadafumi  

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  • Sign of Hall coefficient in nearest-neighbor hopping conduction in heavily Al-doped p-type 4H-SiC

    Matsuura, Hideharu   Takeshita, Akinobu   Hidaka, Atsuki   Ji, Shiyang   Eto, Kazuma   Mitani, Takeshi   Kojima, Kazutoshi   Kato, Tomohisa   Yoshida, Sadafumi   Okumura, Hajime  

    We have observed negative Hall coefficients [R-H(T)] in a nearest-neighbor hopping (NNH) conduction region in epilayers of heavily Al-doped or Al-N co-doped p-type 4H-SiC grown on n-type 4H-SiC substrates by CVD or in wafers of heavily Al-N co-doped p-type 4H-SiC fabricated by solution growth. We propose a simple physical model to explain the sign of R-H(T) in NNH conduction. According to this model, R-H(T) becomes positive when the Fermi level (E-F) is higher than the Al acceptor level (E-Al), that is, the Fermi-Dirac distribution function f(E-Al) is greater than 0.5, whereas R-H(T) becomes negative when E-F is lower than E-Al, which occurs at low temperatures. Because the dominant conduction mechanisms in heavily Al-doped or Al-N co-doped p-type 4H-SiC with Al concentrations on the order of 10(19) cm(-3) are band and NNH conduction at high and low temperatures, respectively, the proposed model can explain why R-H(T) becomes negative at low temperatures.
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  • Experiment on alleviating the bending of CVD-grown heavily Al-doped 4H-SiC epiwafer by codoping of N

    Ji, Shi-yang   Kojima, Kazutoshi   Ishida, Yuuki   Saito, Shingo   Yamaguchi, Hirotaka   Yoshida, Sadafumi   Tsuchida, Hidekazu   Okumura, Hajime  

    In order to alleviate the convex wafer bow that commonly occurs on a heavily Al-doped 4H-SiC epilayer grown on an n(+) substrate, nitrogen gas was intentionally introduced, together with an Al dopant gas during CVD growth, that is Al-N codoping. It was found that, by introducing N-2 at various flow rates, the concentration of incorporated N impurity increases along with the supplied flow rate, while the Al impurity remains at a similar concentration. With the codoping of N and Al in 4H-SiC, a marked reduction of wafer bow has been achieved. The crystal structural measurement suggests that the introduction of N impurity alleviates the large wafer bow owing to the reduced lattice constant differences between the p(+) epilayer and the n(+) substrate. (C) 2015 The Japan Society of Applied Physics
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  • An empirical growth window concerning the input ratio of HCl/SiH4 gases in filling 4H-SiC trench by CVD

    Ji, Shiyang   Kosugi, Ryoji   Kojima, Kazutoshi   Mochizuki, Kazuhiro   Saito, Shingo   Nagata, Akiyo   Matsukawa, Yasuko   Yonezawa, Yoshiyuki   Yoshida, Sadafumi   Okumura, Hajime  

    Two kinds of defective growth in 4H-SiC trench filling were found to be associated with the compositional ratio of supplied gases. An input HCl/SiH4 ratio below 35 leads to overgrowth around the mesa, forming voids. Overetching on the mesa induces an etched mesa when HCl is supplied in excess, e.g., HCl/SiH4 > 65 (SiH4 =3D 30 sccm). Thus, an empirical window for nondefective growth is discerned. It also contains a high-filling-rate area around HCl/SiH4 similar to 50, which proves well-proportioned etching and deposition reactions, and 25-mu m-deep trenches (aspect ratio of similar to 11) are successfully filled at a rate as high as 4.3 mu m/h. (c) 2017 The Japan Society of Applied Physics
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  • The growth of low resistivity, heavily Al-doped 4H-SiC thick epilayers by hot-wall chemical vapor deposition

    Ji, Shiyang   Kojima, Kazutoshi   Ishida, Yuuki   Saito, Shingo   Kato, Tomohisa   Tsuchida, Hidekazu   Yoshida, Sadafumi   Okumura, Hajime  

    Heavily Al-doped 4H-SiC thick epi layers (similar to 90 mu m) were grown on 3-in n(+) 4H-SiC wafers by using the hot-wall CVD method. On the purpose of enhancing incorporated Al-dopant concentration, the growth condition dependence of the Al incorporation behavior in the heavy doping range near Al solubility limit in 4H-SiC was investigated by varying the growth parameters, i.e., growth rate, pressure, temperature and Al-dopant source flow rate. A series of thick epilayers possessing Al-dopant concentration from 9.6 x 10(19) to 4.7 x 10(2) cm(-3) were obtained. Among them, the epilayer with Al-dopant concentration of 3.5 x 10(20) cm(-3) demonstrates a comparably low resistivity of 16.5 m Omega cm as that of commercial n(+) 4H-SiC wafer. The incorporated Al-dopant concentration dependences on surface morphology, crystalline quality and crystal structures of the heavily Al-doped thick epilayers on n(+) 4H-SiC substrates were characterized and discussed. (C) 2013 Elsevier B.V. All rights reserved.
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  • Growth rate enhancement of (0001)-face silicon-carbide oxidation in thin oxide regime RID B-3843-2012 RID B-3902-2012

    Yamamoto, Takeshi   Hijikata, Yasuto   Yaguchi, Hiroyuki   Yoshida, Sadafumi  

    The thermal oxidation of silicon carbide (SiC) has been studied by performing in-situ ellipsometry. We have found that the oxidation rates at the oxidation thickness of approximately less than around 20 nm are much larger than those given using the Deal-Grove (D-G) model, suggesting that the oxidation time dependence of the oxide thickness cannot be explained using the D-G model, i.e., a simple linear-parabolic model, in the initial oxidation stage. By using the empirical relation, which has been proposed for Si oxidation, i.e., adding an exponential term to the D-G equation, the origin of the growth rate enhancement in SiC oxidation has been discussed.
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  • Oxide Growth Rate Enhancement of Silicon Carbide (0001) Si-Faces in Thin Oxide Regime RID B-3843-2012 RID B-3902-2012

    Yamamoto, Takeshi   Hijikata, Yasuto   Yaguchi, Hiroyuki   Yoshida, Sadafumi  

    Thermal oxidation process of silicon carbide (SiC) has been studied by performing in-situ spectroscopic ellipsometry. In our previous work, we, for the first time, found that the growth rates of SiC(000 (1) over bar) C-face at oxidation thicknesses less than around 20 nm are much higher than those given by the Deal-Grove (D-G) model. In this report, we show that such a growth rate enhancement occurs also in the oxidation of SiC(0001) Si-face. By applying the empirical equation proposed by Massoud et al. [J. Electrochem. Soc. 132 (1985) 2685] to the oxidation of SiC Si-face and comparing the temperature and oxygen partial pressure dependences of oxidation rate parameters obtained with those for C-face, we discuss the difference in oxidation mechanism between SiC Si- and C-faces. [DOI: 10.1143/JJAP.47.7803]
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  • Semiconductor heterostructures and superlattices.

    YOSHIDA, Sadafumi  

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