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.

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.

Nanoparticle-Decorated Ultrathin La2O3 Nanosheets as an Effcient Electrocatalysis for Oxygen Evolution Reactions

Electrochemical catalysts for oxygen evolution reaction are a critical component for many renewable energy applications. To improve their catalytic kinetics and mass activity are essential for sustainable industrial applications. Here, we report a rare-earth metal-based oxide electrocatalyst comprised of ultrathin amorphous La2O3 nanosheets hybridized with uniform La2O3 nanoparticles(La2O3@NP-NS). Significantly improved OER performance is observed from the nanosheets with a nanometer-scale thickness. The as-synthesized 2.27-nm La2O3@NP-NS exhibits excellent catalytic kinetics with an overpotential of 310 mV at 10 m A cm^-2, a small Tafel slope of 43.1 mV dec^-1, and electrochemical impedance of 38 Ω. More importantly, due to the ultrasmall thickness, its mass activity, and turnover frequency reach as high as 6666.7 A g^-1 and 5.79 s^-1, respectively, at an overpotential of 310 mV. Such a high mass activity is more than three orders of magnitude higher than benchmark OER electrocatalysts, such as IrO2 and RuO2. This work presents a sustainable approach toward the development of highly e cient electrocatalysts with largely reduced mass loading of precious elements.

Ultrathin two-dimensional medium-entropy oxide as a highly efficient and stable electrocatalyst for oxygen evolution reaction

Medium-entropy oxides(MEOs)with broad compositional tunability and entropy-driven structural stability,are receiving booming attention as a promising candidate for oxygen evolution reaction(OER)electrocatalysts.Meanwhile,ultrathin two-dimensional(2D)nanostructure offers extremely large specific surface area and is therefore considered to be an ideal catalyst structure.However,it remains a grant challenge to synthesize ultrathin 2D MEOs due to distinct nucleation and growth kinetics of constituent multimetallic elements in 2D anisotropic systems.In this work,an ultrathin 2D MEO(MnFeCoNi)O was successfully synthesized by a facile and low-temperature ionic layer epitaxy method.Benefiting from multi-metal synergistic effects within ultrathin 2D nanostructure,this 2D MEO(MnFeCoNi)O revealed excellent OER electrocatalytic performance with a quite low overpotential of 117 mV at 10 mA·cm^(-2) and an impressive stability for 120 h continuous operation with only 6.9%decay.Especially,the extremely high mass activity(5584.3 A·g^(-1))was three orders of magnitude higher than benchmark RuO_(2)(3.4 A·g^(-1))at the same overpotential of 117 mV.This work opens up a new avenue for developing highly efficient and stable electrocatalysts by creating 2D nanostructured MEOs.

Transmission-mode GaN photocathode based on graded Al_xGa_(1-x)N buffer layer

We create a GaN photocathode based on graded AlxGa1-xN buffer layers to overcome the influence of buffer-emission layer interface on the photoemission of transmission-mode GaN photocathodes. A gate- shaped spectral response with a 260-nm starting wavelength and a 375-nm cut-off wavelength is obtained. Average quantum efficiency is 15% and short wavelength responses are almost equivalent to long wavelength ones. The fitted interface recombination velocity is 5×10^4 cm/s, with negligible magnitude, proving that the design of the graded buffer layers is efficient in obtaining good interface quality between the buffer and the emission laver.

Steady-state solution growth of microcrystalline silicon on nanocrystalline seed layers on glass

The growth of polycrystalline silicon layers on glass from tin solutions at low temperatures is presented.This approach is based on the steady-state solution growth of Si crystallites on nanocrystalline seed layers, which are prepared in a preceding process step. Scanning electron microscopy and atomic force microscopy investigations reveal details about the seed layer surfaces, which consist of small hillocks, as well as about Sn inclusions and gaps along the glass substrate after solution growth. The successful growth of continuous microcrystalline Si layers with grain sizes up to several ten micrometers shows the feasibility of the process and makes it interesting for photovoltaics.

Chemical mechanical polishing of freestanding GaN substrates

Chemical mechanical polishing （CMP） has been used to produce smooth and scratch-free surfaces for GaN. In the aqueous solution of KOH, GaN is subjected to etching. At the same time, all surface irregularities, including etch pyramids, roughness after mechanical polishing and so on will be removed by a polishing pad. The experiments had been performed under the condition of different abrasive particle sizes of the polishing pad. Also the polishing results for different polishing times are analyzed, and chemical mechanical polishing resulted in an average root mean square （RMS） surface roughness of 0.565 nm, as measured by atomic force microscopy.

Current-voltage characteristics simulation and analysis of 4H-SiC metal-semiconductor-metal ultraviolet photodetectors

The current-voltage （I-V） characteristics of 4H-SiC metal-semiconductor-metal （MSM） ultraviolet photodetector with different finger widths and spacings, different carrier concentrations and thicknesses of n-type epitaxial layer are simulated. The simulation results indicate that the dark current and the photocurrent both increase when the finger width increases. But the effect of finger width on the dark current is more significant. On the other hand, the effect of finger spacing on the photocurrent is more significant. When the finger spacing increases, the photocurrent decreases and the dark current is almost changeless. In addition, it is found that the smaller the carrier concentration of n-type epitaxial layer is, the smaller the dark current and the larger the photocurrent will be. It is also found that I-V characteristics of MSM detector also depend on the epitaxial layer thickness. The dark current of detector is smaller and the photocurrent is larger when the epitaxial layer thickness is about 3μm.

A novel structure in reducing the on-resistance of a VDMOS

A novel structure of a VDMOS in reducing on-resistance is proposed. With this structure, the specific on-resistance value of the VDMOS is reduced by 22% of that of the traditional VDMOS structure as the breakdown voltage maintained the same value in theory, and there is only one additional mask in processing the new structure VDMOS, which is easily fabricated. With the TCAD tool, one 200 V N-channel VDMOS with the new structure is analyzed, and simulated results show that a specific on-resistance value will reduce by 23%, and the value by 33% will be realized when the device is fabricated in three epitaxies and four buried layers. The novel structure can be widely used in the strip-gate VDMOS area.

An improved analytical model for the electric field distribution in an RF-LDMOST structure

This paper presents an improved analytical model for an RF-LDMOST structure based on the 2D Poisson equation. The derived model indicates the influence of high doped shallow drift and low doping concentration p epitaxial layer on the electric field distribution. In particular, the importance of the thickness of the p epitaxial layer for electric field distributions in RF-LDMOST are shown through MATLAB analytical results based on the model. Then ISE TCAD simulations and experiments are processed and their results are in agreement with the analytical model. This model contributes to the comprehension and optimization design of RF-LDMOST.

In vitro study of enhanced photodynamic cancer cell killing effect by nanometer-thick gold nanosheets

Photodynamic therapy(PDT)by near-infrared(NIR)irradiation is a promising technique for treating various cancers.Here,we reported the development of free-standing wafer-scale Au nanosheets(NSs)that exhibited an impressive PDT effect.The Au NSs were synthesized by ionic layer epitaxy at the air-water interface with a uniform thickness in the range from 2 to 8.5 nm.These Au NSs were found very effective in generating singlet oxygen under NIR irradiation.In vitro cellular study showed that the Au NSs had very low cytotoxicity and high PDT efficiency due to their uniform 2D morphology.Au NSs could kill cancer cells after 5 min NIR irradiation with little heat generation.This performance is comparable to using 10 times mass loading of Au nanoparticles(NPs).This work suggests that two-dimensional(2D)Au NSs could be a new type of biocompatible nanomaterial for PDT of cancer with an extraordinary photon conversion and cancer cell killing efficiency.