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SiC epitaxial layers grown by chemical vapour deposition and the fabrication of Schottky barrier diodes 下载免费PDF全文
This paper presents the results of unintentionally doped
4H-SiC epilayers grown on n-type Si-faced 4H-SiC substrates with 8°
off-axis toward the [11\overline 2 0] direction by low pressure
horizontal hot-wall chemical vapour deposition. Growth temperature
and pressure are 1580~°C and 104~Pa, respectively. Good surface
morphology of the sample is observed using atomic force
microscopy (AFM) and scanning electron microscopy (SEM). Fourier transform
infrared spectroscopy (FTIR) and x-ray diffraction (XRD) are used to
characterize epitaxial layer thickness and the structural quality of the
films respectively. The carrier concentration in the unintentional 4H-SiC
homoepitaxial layer is about 6.4×1014~cm-3 obtained by
c--V measurements. Schottky barrier diodes (SBDs) are fabricated on the
epitaxial wafer in order to verify the quality of the wafer and to obtain
information about the correlation between background impurity and electrical
properties of the devices. Ni and Ti/4H-SiC Schottky barrier diodes with
very good performances were obtained and their ideality factors are 1.10 and 1.05
respectively. 相似文献
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Silicon dioxide (SiO2) layers with a thickness more than 10 nm can be formed at ∼120 °C by direct Si oxidation with nitric acid (HNO3). Si is initially immersed in 40 wt.% HNO3 at the boiling temperature of 108 °C, which forms a ∼1 nm SiO2 layer, and the immersion is continued after reaching the azeotropic point (i.e., 68 wt.% HNO3 at 121 °C), resulting in an increase in the SiO2 thickness. The nitric acid oxidation rates are the same for (1 1 1) and (1 0 0) orientations, and n-type and p-type Si wafers. The oxidation rate is constant at least up to 15 nm SiO2 thickness (i.e., 1.5 nm/h for single crystalline Si and 3.4 nm/h for polycrystalline Si (poly-Si)), indicating that the interfacial reaction is the rate-determining step. SiO2 layers with a uniform thickness are formed even on a rough surface of poly-Si thin film. 相似文献
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We have obtained the first experimental evidence for the Pockels effect of water, which is induced by a high electric field in the electric double layer (EDL) on the water-transparent electrode interface. The electric-field induced energy shift of the visible interference fringes of a 300 nm indium-tin-oxide (ITO) electrode layer is observed, indicating a negative refractive index change at the interface. Numerical calculation reproduces well the experimental observation, showing that the signal mainly originates from water in the EDL. The Pockels constants of water are estimated to be r33 = 5.1 × 100 pm/V and r13 = 1.7 × 100 pm/V. The large anisotropy of the Pockels effect of water is deduced from the incidence angle dependence of the p-polarization signal. At the same time, the ITO shows a blue shift of the band gap in the UV due to the band population effect in the space charge layer. The plasma frequency in the near IR is also expected to increase due to the band population effect, since the ITO has a high doped carrier population close to metal. A negative refractive index change in the ITO space charge layer is induced from both effects, but its effect on the signal is estimated to be much smaller than that of the negative refractive index change of water in the EDL. 相似文献
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Takashi Sato Masakiyo Tsunoda Migaku Takahashi 《Journal of magnetism and magnetic materials》2002,240(1-3):277-279
Correlation between the unidirectional anisotropy constant, JK, and the degree of ordering of PtMn layer was investigated for Pt55Mn45/Co90Fe10 bilayer, as a function of the annealing time and the PtMn layer thickness, dAF. As a result, we found the linear relations between JK and the degree of ordering, fFCT·S, in the cases of the bilayers with dAF=5–50 nm. From the extrapolation of the linear relations to fFCT·S=1, meaning the perfect ordering of PtMn layer, we obtained the attainable value of JK and the intrinsic critical thickness of the PtMn layer to be 0.26 erg/cm2 and 6 nm, respectively. 相似文献
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Tuning of the open‐circuit voltage by wide band‐gap absorber and doped layers in thin film silicon solar cells 下载免费PDF全文
Shuo Wang Vladimir Smirnov Tao Chen Xiaodan Zhang Shaozhen Xiong Ying Zhao Friedhelm Finger 《固体物理学:研究快报》2015,9(8):453-456
We present an experimental study combined with computer simulations on the effects of wide band‐gap absorber and window layers on the open‐circuit voltage (Voc) in single junction thin film silicon solar cells. The quantity ΔEp, taking as the difference between the band gap and the activation energy in ?p? layer, is treated as a measure of the p‐layer properties and shows a linear relation with Voc over a range of 100 mV with a positive slope of around 430 mV/eV. Two limiting mechanisms of Voc are identified: the built‐in potential at lower ΔEp and the band gap of the absorber layer at higher ΔEp. The results of the experimental findings are confirmed by computer simulations. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
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A protocol for searching the most probable phase‐retrieved maps in coherent X‐ray diffraction imaging by exploiting the relationship between convergence of the retrieved phase and success of calculation 下载免费PDF全文
Yuki Sekiguchi Saki Hashimoto Amane Kobayashi Tomotaka Oroguchi Masayoshi Nakasako 《Journal of synchrotron radiation》2017,24(5):1024-1038
Coherent X‐ray diffraction imaging (CXDI) is a technique for visualizing the structures of non‐crystalline particles with size in the submicrometer to micrometer range in material sciences and biology. In the structural analysis of CXDI, the electron density map of a specimen particle projected along the direction of the incident X‐rays can be reconstructed only from the diffraction pattern by using phase‐retrieval (PR) algorithms. However, in practice, the reconstruction, relying entirely on the computational procedure, sometimes fails because diffraction patterns miss the data in small‐angle regions owing to the beam stop and saturation of the detector pixels, and are modified by Poisson noise in X‐ray detection. To date, X‐ray free‐electron lasers have allowed us to collect a large number of diffraction patterns within a short period of time. Therefore, the reconstruction of correct electron density maps is the bottleneck for efficiently conducting structure analyses of non‐crystalline particles. To automatically address the correctness of retrieved electron density maps, a data analysis protocol to extract the most probable electron density maps from a set of maps retrieved from 1000 different random seeds for a single diffraction pattern is proposed. Through monitoring the variations of the phase values during PR calculations, the tendency for the PR calculations to succeed when the retrieved phase sets converged on a certain value was found. On the other hand, if the phase set was in persistent variation, the PR calculation tended to fail to yield the correct electron density map. To quantify this tendency, here a figure of merit for the variation of the phase values during PR calculation is introduced. In addition, a PR protocol to evaluate the similarity between a map of the highest figure of merit and other independently reconstructed maps is proposed. The protocol is implemented and practically examined in the structure analyses for diffraction patterns from aggregates of gold colloidal particles. Furthermore, the feasibility of the protocol in the structure analysis of organelles from biological cells is examined. 相似文献