Influence of epitaxial layer structure and cell structure on electrical performance of 6.5 kV SiC MOSFET

Silicon carbide(SiC)material features a wide bandgap and high critical breakdown field intensity.It also plays an important role in the high efficiency and miniaturization of power electronic equipment.It is an ideal choice for new power electronic devices,especially in smart grids and high-speed trains.In the medium and high voltage fields,SiC devices with a blocking voltage of more than 6.5 kV will have a wide range of applications.In this paper,we study the influence of epitaxial material properties on the static characteristics of 6.5 kV SiC MOSFET.6.5 kV SiC MOSFETs with different channel lengths and JFET region widths are manufactured on three wafers and analyzed.The FN tunneling of gate oxide,HTGB and HTRB tests are performed and provide data support for the industrialization process for medium/high voltage SiC MOSFETs.

Raman Study of Defects in SI－GaAs and Se－doped Epitaxial Layer Irradiated by 10 MeV Electrons

Raman scattering measurements on Se-doped GaAs epitaxial layers and semi-insulating (SI) GaAs irradi-ated by 10 Mev electrons have been investigated. Several defect-related features were observed. We suggestthat the 220 cm ￣-1mode is attribute to As_1 which is associated, at least in part, with EL2 and EL12 defects.For Sedoped samples, the Raman peaks at 205 and 258 cm￣-1 may be due to vibrational modes in small clus-ters of arsenic, and the 77 and 185 ￣-1modes are probably associated with disorder-activated first order Ra-man scattering.Irradiated results show that the small clusters of arsenic and disorder state are increased with in-creasing irradiation fluences. Other Raman peaks will also be discussed in this paper.

Quantitative Evaluation of an Epitaxial Silicon-Germanium Layer on Silicon

An epitaxial SixGey layer on a silicon substrate was quantitatively evaluated using rocking curve (RC) and reciprocal space map (RSM) obtained by powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) in conjunction with transmission electron microscopy (TEM), and EDS in conjunction with scanning electron microscopy (SEM). To evaluate the relative deviation of the quantitative analysis results obtained by the RC, RSM, SEM/EDS, and TEM/EDS methods, a standard sample comprising a Si0.7602Ge0.2398 layer on a Si substrate was used. The correction factor (K-factor) for each technique was determined using multiple measurements. The average and standard deviation of the atomic fraction of Ge in the Si0.7602Ge0.2398 standard sample, as obtained by the RC, RSM, TEM/EDS, and SEM/EDS methods, were 0.2463 ± 0.0016, 0.2460 ± 0.0015, 0.2350 ± 0.0156, and 0.2433 ± 0.0059, respectively. The correction factors for the RC, RSM, TEM/EDS, and SEM/EDS methods were 0.9740, 0.9740, 1.0206, and 0.9856, respectively. The SixGey layer on a silicon substrate was quantitatively evaluated using the RC, RSM, and EDS/TEM methods. The atomic fraction of Ge in the epitaxial SixGey layer, as evaluated by the RC and RSM methods, was 0.1833 ± 0.0007, 0.1792 ± 0.0001, and 0.1631 ± 0.0105, respectively. After evaluating the results of the atomic fraction of Ge in the epitaxial layer, the error was very small, i.e., less than 3%. Thus, the RC, RSM, TEM/EDS, and SEM/EDS methods are suitable for evaluating the composition of Ge in epitaxial layers. However, the thickness of the epitaxial layer, whether the layer is strained or relaxed, and whether the area detected in the TEM and SEM analyses is consistent must be considered.

Direct Structural Evidences of Epitaxial Growth Ge<SUB>1-X</SUB>Mn<SUB>X</SUB>Nanocolumn Bi-Layers on Ge(001)

Molecular Beam Epitaxy (MBE) system equipped with in-situ Reflection High-Energy Electron Diffraction (RHEED) has been used for (Ge, Mn) thin film growth and monitoring the surface morphology and crystal structure of thin films. Based on the observation of changes in RHEED patterns during nanocolumn growth, we used a real-time control approach to realize multilayer structures that consist of two nanocolumn layers separated by a Ge barrier layer. Transmission Electron Microscopy (TEM) has been used to investigate the structural properties of the GeMn nanocolumns and GeMn/Ge nanocolumns bi-layers samples.

Fabricating Buffer Layers for YBa_2Cu_3O_y Coated Conductor by Surface Oxidation Epitaxy

NiO buffer layers were formed on a tape of Ni for making YBCO coated conductor by surface-oxidation epitaxy （SOE） process. Different oxidizing conditions such as temperature and duration were studied for Ni tapes. It is found that the texture of NiO could be affected directly by the orientation and surface of substrate. X-ray diffraction （XRD） 2-2θ scan, φ-scan, and pole figure were employed to characterize the in-plane alignment and cube texture. X-ray φ-scan shows that NiO film is formed on Ni tape with high cube texture and a typical value at the full width at half maximum （FWHM） is ≤ 7.5°. Scanning electron microscopy was used to study the surface morphology of NiO films. No crack is found and the films appear dense. Such technique is simple and of low cost with perfect reproducibility, promising for developing long tapes.

Dielectric Response and Broadband Microwave Absorption Properties of Three-Layer Graded ZnO Nanowhisker/Polyester Composites

We design and prepare three-layer graded ZnO nanowhisker/polyester composites. The dispersion configuration of ZnO nanowhiskers in the polyester is investigated, and their microwave reflectivity curves are also measured. Experimental results have shown that the graded dispersion with ZnO nanowhiskers contributes to broadband microwave absorption. In other words, the absorption band depends on the graded dispersion configuration of ZnO nanowhiskers in polyester matrix.

Two Phases of Coherent Structure Motions in Turbulent Boundary Layer

Two phases of coherent structure motion are acquired after obtaining conditional phase-averaged waveforms for longitudinal velocity of coherent structures in turbulent boundary layer based on Harr wavelet transfer. The correspondences of the two phases to the two processes （i.e. ejection and sweep） during a burst are determined.

Boundary Layer on a Moving Wall with Suction and Injection

We investigate the boundary-layer flow on a moving permeable plate parallel to a moving stream. The governing equations are solved numerically by a finite-difference method. Dual solutions are found to exist when the plate and the free stream move in the opposite directions.

Boundary Layer Flow over a Continuously Moving Thin Needle in a Parallel Free Stream

We investigate the boundary-layer flow on a moving isothermal thin needle parallel to a moving stream. The governing equations are solved numerically by a finite-difference method. Dual solutions are found to exist when the needle and the free stream move in the opposite directions.

NONDESTRUCTIVE BAND-GAP PROFILE DETERMINATION OF HgCdTe LPE GROWN LAYERS

Infrared transmission and photoconductivity spectra of mercury cadmium telluride (MCT) epitaxial layers, grown by liquid phase epitaxy (LPE) on CdTe and CdZnTe wide band gap substrates, were investigated both theoretically and experimentally at temperatures T =82 K and T =300 K in the infrared (IR) wavelength region 3 15 μm. The photoresponse position of the diodes was determined at cryogenic temperatures from the transmission spectra of room temperature. Theoretical calculations of optical density D(h-ω), needed for analysis of experimental optical transmission data, were performed in the framework of WKB approximation.

Research on CeO2 cap layer for YBCO-coated conductor

Two groups of coated conductor samples with different thicknesses of CeO2 cap layers deposited by pulsed laser deposition （PLD） under the same conditions have been studied. Of them, one group is of CeO2 films, which are deposited on stainless steel （SS） tapes coated by IBAD-YSZ （IBAD-YSZ/SS）, and the other group is of CeO2/YSZ/Y2O3 multilayers, which are deposited on NiW substrates by PLD for the fabrication of YBCO-coated conductor through the RABiTS approach. YBCO film is then deposited on the tops of both types of buffer layers by PLD. The effects of the thickness of the CeO2 film on the texture of the CeO2 film and the critical current density （Jc） of the YBCO film are analysed. For the case of CeO2 film on IBAD-YSZ/SS, there appears a self-epitaxy effect with increasing thickness of the CeO2 film. For CeO2/YSZ/Y2O3/NiW, in which the buffer layers are deposited by PLD, there occurs no self-epitaxy effect, and the optimal thickness of CeO2 is about 50 nm. The surface morphologies of the two groups of samples are examined by SEM.

Epitaxial Properties of Co-Doped ZnO Thin Films Grown by Plasma Assisted Molecular Beam Epitaxy

High quality Co-doped ZnO thin films are grown on single crystalline Al2O3（0001） and ZnO（0001） substrates by oxygen plasma assisted molecular beam epitaxy at a relatively lower substrate temperature of 450℃. The epitaxial conditions are examined with in-situ reflection high energy electron diffraction （RHEED） and ex-situ high resolution x-ray diffraction （HRXRD）. The epitaxial thin films are single crystal at film thickness smaller than 500nm and nominal concentration of Co dopant up to 20%. It is indicated that the Co cation is incorporated into the ZnO matrix as Co^2＋ substituting Zn^2＋ ions. Atomic force microscopy shows smooth surfaces with rms roughness of 1.9 nm. Room-temperature magnetization measurements reveal that the Co-doped ZnO thin films are ferromagnetic with Curie temperatures Tc above room temperature.

An Electroluminescence Delay Time Model of Bilayer Organic Light-Emitting Diodes

Based on the mechanism of injection, transport and recombination of the charge carriers, we develop a model to calculate the delay time of electroluminescence （EL） from bilayer organic light emitting diodes. The effect of injection, transport and recombination processes on the EL delay time is discussed, and the relationship between the internal interface barrier and the recombination time is revealed. ＂]~he results show that the EL delay time is dominated by the recombination process at lower applied voltage and by the transport process at higher applied voltage. When the internal interface barrier varies from 0.15 eV to 0.3 eV, the recombination delay time increases rapidly~ while the internal interface barrier exceeds about 0.3eV~ the dependence of the recombination delay time on applied voltage is almost undiversified, which may serve as a guideline for designing of a high-speed EL response device.

Reduction of Dislocations in GaN Epilayer Grown on Si （111） Substrates using a GaN Intermedial Layer

GaN intermedial layers grown under different pressures are inserted between GaN epilayers and AIN/Si（111） substrates. In situ optical reflectivity measurements show that a transition from the three-dimensional （3D） mode to the 2I） one occurs during the GaN epilayer growth when a higher growth pressure is used during the preceding GaN intermedial layer growth, and an improvement of the crystalline quality of GaN epilayer will be made. Combining the in situ reflectivity and transmission electron microscopy （TEM） measurements, it is suggested that the lateral growth at the transition of growth mode is favourable for bending of dislocation lines, thus reducing the density of threading dislocations in the epilayer.

Study of a 4H-SiC epitaxial n-channel MOSFET

Epitaxial channel metal-oxide semiconductor field-effect transistors （MOSFETs） have been proposed as one possible way to avoid the problem of low inversion layers in traditional MOSFETs. This paper presents an equation of maximum depletion width modified which is more accurate than the original equation. A 4H--SiC epitaxial n-channel MOSFET using two-dimensional simulator ISE is simulated. Optimized structure would be realized based on the simulated results for increasing channel mobility.

A new algorithm based on C-V characteristics to extract the epitaxy layer parameters for power devices with the consideration of termination

Doping concentration and thickness of an epitaxy layer are the most essential parameters for power devices.The conventional algorithm extracts these two parameters by calculating the doping profile from its capacitance-voltage(C-V)characteristics.Such an algorithm treats the device as a parallel-plane junction and ignores the influence of the terminations.The epitaxy layer doping concentration tends to be overestimated and the thickness underestimated.In order to obtain the epitaxy layer parameters with higher accuracy,a new algorithm applicable for devices with field limited ring(FLR)terminations is proposed in this paper.This new algorithm is also based on the C-V characteristics and considers the extension manner of the depletion region under the FLR termination.Such an extension manner depends on the design parameters of the FLR termination and is studied in detail by simulation and modeling.The analytical expressions of the device C-V characteristics and the effective doping profile are derived.More accurate epitaxy layer parameters can be extracted by fitting the effective doping profile expression to the C-V doping profile calculated from the C-V characteristics.The relationship between the horizontal extension width and the vertical depth of the depletion region is also acquired.The credibility of the new algorithm is verified by experiments.The applicability of our new algorithm to FLR/field plate combining terminations is also discussed.Our new algorithm acts as a powerful tool for analyses and improvements of power devices.

Hydrogen Passivation Effect on Enhanced Luminescence from Nanocrystalline Si/SiO2 Multilayers

Nanocrystalline Si/SiO2 multilayers are prepared by thermally annealing amorphous Si/SiO2 stacked structures. The photoluminescence intensity is obviously enhanced after hydrogen passivation at various temperatures. It is suggested that the hydrogen trapping and detrapping processes at different temperatures strongly influence the passivation effect. Direct experimental evidence is given by electron spin resonance spectra that hydrogen effectively reduces the nonradiative defect states existing in the Si nanocrystas/SiO2 system which enhances the radiative recombination probability. The luminescence characteristic shows its stability after hydrogen passivation even after aging eight months.

Two-Player and Two-Strategy Symmetric Evolutionary Game with Fluctuations

Research on evolutionary games in a noisy environment is still a non-solved problem. By using Markov process, we build a dynamic model for two-player and two-strategy symmetric game in noisy environment. Some illustrative examples are presented and the results are determined by simulation experiments.