Magnetocaloric properties of Nd-doped Gd5Si4 microparticles and nanopowders

The preparation of materials with enhanced magnetocaloric properties is crucial for magnetic refrigeration. In thisstudy, Nd-doped Gd5Si4 microparticles and nanomaterials were synthesized using the reduction–diffusion method. Theimpact of Nd doping with varying compositions on the structure and entropy change properties of the materials was investigated.The Curie temperatures of both the micron- and nano-sized materials ranged from 190 K to 210 K, which were lowerthan previously reported values. Micron-sized samples doped with 1% Nd exhibited superior magnetocaloric properties,demonstrating a maximum entropy change of 4.98 J·kg^(-1)·K^(-1) at 5 T, with an entropy change exceeding 4 J·kg^(-1)·K^(-1)over a wide temperature range of approximately 70 K. Conversely, the nanomaterials had broader entropy change peaks butlower values. All samples exhibited a second-order phase transition, as confirmed by the Arrott plots.

A two-dimensional analytical model for channel potential and threshold voltage of short channel dual material gate lightly doped drain MOSFET

An analytical model for the channel potential and the threshold voltage of the short channel dual-material-gate lightly doped drain （DMG-LDD） metal-oxide-semiconductor field-effect transistor （MOSFET） is presented using the parabolic approximation method. The proposed model takes into account the effects of the LDD region length, the LDD region doping, the lengths of the gate materials and their respective work functions, along with all the major geometrical parameters of the MOSFET. The impact of the LDD region length, the LDD region doping, and the channel length on the channel potential is studied in detail. Furthermore, the threshold voltage of the device is calculated using the minimum middle channel potential, and the result obtained is compared with the DMG MOSFET threshold voltage to show the improvement in the threshold voltage roll-off. It is shown that the DMG-LDD MOSFET structure alleviates the problem of short channel effects （SCEs） and the drain induced barrier lowering （DIBL） more efficiently. The proposed model is verified by comparing the theoretical results with the simulated data obtained by using the commercially available ATLASTM 2D device simulator.

Si-doped diamond films prepared by chemical vapour deposition

The effects of Si doping on morphology, components and structure characteristics of CVD diamond films were studied. Si-doped CVD diamond films were deposited on Si substrate by adding tetraethoxysilane （TEOS） into acetone as source of reactant gas. The morphology and microstructure of diamond films were characterized by scanning electron microcopy （SEM）. The crystalline quality of diamond films was studied by Raman spectroscopy and X-ray diffractometry （XRD）. The surface roughness of the films was evaluated with surface profilometer. The results suggest that Si doping tends to reduce the crystallite size, enhance grain refinement and inhibit the appearance of （11 I） facets. Raman spectra indicate that Si doping can enhance the formation of sp2 phase in diamond films. Moreover, Raman signal of SiC was detected, which suggests the existence of Si in the diamond films. Smooth fine-grained diamond （SFGD） film was synthesized at Si to C ratio of 1%.

Novel vertical stack HCMOSFET with strained SiGe/Si quantum channel

A novel vertical stack heterostructure CMOSFET is investigated, which is structured by strained SiGe/Si with a hole quantum well channel in the compressively strained Sil-xGex layer for p-MOSFET and an electron quantum well channel in the tensile strained Si layer for n-MOSFET. The device possesses several advantages including： 1） the integration of electron quantum well channel with hole quantum well channel into the same vertical layer structure; 2） the gate work function modifiability due to the introduction of poly-SiGe as a gate material; 3） better transistor matching; and 4） flexibility of layout design of CMOSFET by adopting exactly the same material lays for both n-channel and p-channel. The MEDICI simulation result shows that p-MOSFET and n-MOSFET have approximately the same matching threshold voltages. Nice performances are displayed in transfer characteristic, transconductance and cut-off frequency. In addition, its operation as an inverter confirms the CMOSFET structured device to be normal and effective in function.

Refinement of primary Si grains of A390 alloy slurry through serpentine channel pouring process

In this paper, the serpentine channel pouring process for preparing a semi-solid A390 alloy slurry and refining the primary Si grains of the A390 alloy, was used. The effects of the pouring temperature, the cooling water flow and the number of the curves on the size of the primary Si grains in the semi-solid A390 alloy slurry were investigated. The results show that the pouring temperature, the cooling water flow and the number of the curves have a major effect on the size and the distribution of primary Si grains. Under the experimental condition of the four-curve copper channel whose cooling water flow was 500 L·h-1 and the pouring temperature was 690 oC, the primary Si grains of the semi-solid A390 alloy slurry were refined to the greatest extent and the lath-like grains were changed into granular ones. Additionally, the equivalent grain diameter and the average shape factor of the primary Si grains of the satisfactory semi-solid A390 alloy slurry are 18.6 μm and 0.8, respectively. Further, the refinement mechanism of the primary Si grains through the serpentine channel pouring process was analyzed and discussed. In summary, the primary Si nuclei could be easily precipitated due to the chilling effect of the channel inner wall, thus the primary Si grains were greatly refined. Meanwhile, the subsequent alloy melt fluid also promoted the separation of primary Si grains from the inner wall, further refining the primary Si grains.

Effect of Si doping in wells of AlGaN/GaN superlattice on the characteristics of epitaxial layer

An A1GaN/GaN superlattice grown on the top of a GaN buffer induces the broadening of the full width at half maximum of （102） and （002） X-ray diffraction rocking curves. With an increase in the Si-doped concentration in the GaN wells, the full width at half maximum of the （102） rocking curves decreases, while that of the （002） rocking curves increases. A significant increase of the full width at the half maximum of the （002） rocking curves when the doping concentration reaches 2.5 × 10^19 cm-3 indicates the substantial increase of the inclined threading dislocation. High level doping in the A1GaN/GaN superlattice can greatly reduce the biaxial stress and optimize the surface roughness of the structures grown on the top of it.

Si-doped composite carbon as anode of lithium ion batteries

Si doped composite material was prepared by coating artificial graphite with the mixture of phenol resin and polysilicone and following with heat treatment at 1 050 ℃ in an argon gas atmosphere. The structure and characteristics of the composite carbon were determined by means of XRD, SEM, BET surface area and electrochemical measurements. The new carbon material has a disordered carbon/graphite composite structure, with silicon doped in the disordered carbon. Compared with the pristine graphite, the electrochemical performance is improved for the Si doped composite carbon with large reversible capacity of 312.6 mAh/g, high initial charge/discharge efficiency of 88.61%, and excellent cycle stability. The prototype batteries using the composite carbon as anode material have large discharge capacity of 845 mAh and high capacity retention ratio of 95.80% at the 200th cycle.

Effects of Si δ-Doping Condition and Growth Interruption on Electrical Properties of InP-Based High Electron Mobility Transistor Structures

The InGaAs/InAIAs/InP high electron mobility transistor （HEM：F） structures with lattice-matched and pseudo- morphic channels are grown by gas source molecular beam epitaxy. Effects of Si ^-doping condition and growth interruption on the electrical properties are investigated by changing the Si-cell temperature, doping time and growth process. It is found that the optimal Si ^-doping concentration （Nd） is about 5.0 x 1012 cm-2 and the use of growth interruption has a dramatic effect on the improvement of electrical properties. The material structure and crystal interface are analyzed by secondary ion mass spectroscopy and high resolution transmission elec- tron microscopy. An InGaAs/InAiAs/InP HEMT device with a gate length of lOOnm is fabricated. The device presents good pinch-off characteristics and the kink-effect of the device is trifling. In addition, the device exhibits fT = 249 GHa and fmax 〉 400 GHz.

Enhancement of radiation hardness of InP-based HEMT with double Si-doped plane

An anti-radiation structure of In P-based high electron mobility transistor(HEMT) has been proposed and optimized with double Si-doped planes. The additional Si-doped plane under channel layer has made a huge promotion in channel current, transconductance, current gain cut-off frequency, and maximum oscillation frequency of In P-based HEMTs. Moreover, direct current(DC) and radio frequency(RF) characteristic properties and their reduction rates have been compared in detail between single Si-doped and double Si-doped structures after 75-keV proton irradiation with dose of 5× 10^(11) cm^(-2),1× 10^(12) cm^(-2), and 5× 10^(12) cm^(-2). DC and RF characteristics for both structures are observed to decrease gradually as irradiation dose rises, which particularly show a drastic drop at dose of 5× 10^(12) cm^(-2). Besides, characteristic degradation degree of the double Si-doped structure is significantly lower than that of the single Si-doped structure, especially at large proton irradiation dose. The enhancement of proton radiation tolerance by the insertion of another Si-doped plane could be accounted for the tremendously increased native carriers, which are bound to weaken substantially the carrier removal effect by irradiation-induced defects.

Electronic structures and optical properties of Si-and Sn-doped β-Ga_2O_3: A GGA+U study

The electronic structures and optical properties of β-Ga_2O_3 and Si-and Sn-doped β-Ga_2O_3 are studied using the GGA + U method based on density functional theory. The calculated bandgap and Ga 3d-state peak of β-Ga_2O_3 are in good agreement with experimental results. Si-and Sn-doped β-Ga_2O_3 tend to form under O-poor conditions, and the formation energy of Si-doped β-Ga_2O_3 is larger than that of Sn-doped β-Ga_2O_3 because of the large bond length variation between Ga–O and Si–O. Si-and Sn-doped β-Ga_2O_3 have wider optical gaps than β-Ga_2O_3, due to the Burstein–Moss effect and the bandgap renormalization effect. Si-doped β-Ga_2O_3 shows better electron conductivity and a higher optical absorption edge than Sn-doped β-Ga_2O_3, so Si is more suitable as a dopant of n-type β-Ga_2O_3, which can be applied in deep-UV photoelectric devices.

The effect of substrate doping on the flatband and threshold voltages of a strained-Si pMOSFET

The effect of substrate doping on the flatband and threshold voltages of a strained-Si/SiGe p metal-oxide semiconductor field-effect transistor（pMOSFET） has been studied.By physically deriving the models of the flatband and threshold voltages,which have been validated by numerical simulation and experimental data,the shift in the plateau from the inversion region to the accumulation region as the substrate doping increases has been explained.The proposed model can provide a valuable reference to the designers of strained-Si devices and has been implemented in software for extracting the parameters of a strained-Si MOSFET.

STRUCTURE,CHEMICAL BONDS AND THER MOELECTIC PROPERTY OF Si DOPED BORON CARBIDES

Thecorrelation between composition, structure, chemical bond, and thermoelectric proper tiesof Si doped boroncarbidesisstudied using SCF DV Xαmethod. Thecalculationsshow that Siatom firstlysubstitutes Bor Catomson theend of boron carbidechain, then may occupyinterstitialsites when Siis dopedin boron carbide, anditisdifficultfor SitosubstituteBor Catom in thecenter of chain orintheicosahedron. Arepresentativestructural unitcontain ing an Si atom is 〔C B Si〕ε+ 〔B11 C〕ε , whilethe structural unit without Siis 〔C B B ( C)〕δ 〔B11 C〕δ+ . Afteradding Sitotheboroncarbides,theenergyrequired bythe dispro portionation reaction decreases,theconcentrationofthecarriersincreases,andthereare more pathsfor the bipolaron to hopping. At thesametime, the covalent bond becomes weaker, andthethermal conductivity decreases. Therefore, thethermoelectric property of Si dopedboron carbidesisimproved .

Influence of Si doping on the structural and optical properties of InGaN epilayers

Influences of the Si doping on the structural and optical properties of the InGaN epilayers are investigated in detail by means of high-resolution X-ray diffraction （HRXRD）, photolumimescence （PL）, scanning electron microscope （SEM）, and atomic force microscopy （AFM）. It is found that the Si doping may improve the surface morphology and crystal quality of the InGaN film and meanwhile it can also enhance the emission efficiency by increasing the electron concentration in the InGaN and suppressing tile formation of V-defects, which act as nonradiative recombination centers in the InGaN, and it is proposed that the former plays a more important role in enhancing the emission efficiency in the InGaN.

Interstitial Oxygen Determination in Heavily Doped Silicon with "Peak-height" Method by FT-IR Spectra

Due to ineffectiveness of routine IR-absorption method for determinahon of intershtial oxygen in heavily doped silicon, a 'peak-height' method has been dcveloped. The phosphorus-doped CZ-Si with n=(7.l～l2)× 10~17cm^(-3) was taken as sample for characterization. The calculation results at 300 K and 10 K were ptesented in detail. The'peak-height' method is much simpler than 'short-baseline' and 'curved-baseline' methods.

Effects of edge hydrogenation and Si doping on spin-dependent electronic transport properties of armchair boron–phosphorous nanoribbons

In this article, the spin-dependent electronic and transport properties of the armchair boron–phosphorous nanoribbons（ABPNRs） are mainly studied by using the non-equilibrium Green function method combined with the spin-polarized density function theory. Our calculated electronic structures indicate that the edge hydrogenated ABPNRs exhibit a ferromagnetic bipolar magnetic semiconductor property, and that the Si atom doping can make ABPNRs convert into up-spin dominated half metal. The spin-resolved transport property results show that the doped devices can realize 100% spinfiltering function, and that the interesting negative differential resistance phenomenon can be observed. Our calculations suggest that the ABPNRs can be constructed as a spin heterojunction by introducing Si doping partially, and it would be used as a spin-diode for nano-spintronics in future.

放电等离子烧结Y掺杂Mo-Si-B涂层的高温抗氧化性能

稀土元素的掺杂可提升MoSi_(2)体系涂层的高温抗氧化性能,但稀土元素Y对于MoSi_(2)涂层抗氧化性能的影响机理还尚未明确。以Nb-Si基合金为基体,采用放电等离子烧结技术(SPS)在其表面制备Y掺杂(1 wt.%)的33Mo-62Si-5B(at.%)涂层。通过1250℃高温氧化试验,研究涂层的高温氧化行为以及Y对涂层高温抗氧化性能的影响。结果表明:涂层主要由MoSi_(2)、MoB、Mo_(5)Si_(3)和SiO_(2)相构成,Y在涂层中以Y_(2)Si_(2)O_(7)颗粒的形式弥散分布于SiO_(2)相内部。包覆Mo-Si-B涂层的合金样品在氧化试验初期出现质量损失,其100 h后的氧化增重高于包覆Y掺杂Mo-Si-B涂层的合金样品,表明Y掺杂涂层具有更好的高温抗氧化性能。氧化后涂层表面形成由晶态SiO_(2)、硅硼玻璃相(SiO_(2)-B_(2)O_(3))和Y_(2)Si_(2)O_(7)颗粒构成的氧化膜。阐明Y提升Mo-Si-B涂层抗氧化性能的作用机理:在涂层表面优先形成的Y_(2)O_(3)加速了晶态SiO_(2)和硼硅氧化膜的形成,随后形成的Y_(2)Si_(2)O_(7)阻碍了O的内扩散,使Y掺杂Mo-Si-B涂层抗氧化性能得到提高。

Unintentional Doping Mechanisms in GaAs/Si Films Grown by Metalorganic Chemical Vapor Deposition

To explain different doping effects in a buffer layer,thermally annealed interface,and upper epilayers of GaAs/Si films grown by Metalorganic Chemical Vapor Deposition(MOCVD),the behaviors of unintentional doping in GaAs/Si films are investigated in detail.A third doping mechanism of arsine impurity incorporation during the growth process of GaAs/Si films,apart from conventional mechanisms of gas phase reaction and diffusion from the silicon substrate,is proposed.The experimental results reveal that the doping behavior in the buffer layer studied is determined by the three types of doping mechanisms together.However in the thermally annealed interface and upper epilayers,the third doping mechanism is dominant.According to the third mechanism,the background carrier concentration in GaAs/Si films grown by MOCVD could be properly controlled through the arsine flow rate.

Characteristics of In_(0.52)Al_(0.48)As Grown on InP(100) Substrates by Molecular Beam Epitaxy: Growth Optimisation and Effects of Si Doping

Growth of In0.52Al0.48As epilayers on InP (100) substrates by molecular beam epitaxy at a wide range of substrate tempreatures (470~550℃) and at different Si doping levels has been carried out. Low temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) analyses shaw a strong dependence of the PL and XRD linewidths, XRD intensity ratio (Lepi/Isub), and lattice-mismatch on the substrate temperature. The X-ray diffraction peaks of samples grown at law temperatures show a composition of smaller peaks, indicating the presence of disorder due to alloy clustering. Raman scattering measurements of the same samples show an additional higher energy mode at 273 cm-1 in addition to the InAs-like and AlAs-like longitudinal-optic (LO) phonon modes. Samples doped with Si show an inverted S-shaped dependence of the PL peak energy variation with the temperature which weakens at high doping levels due to a possible reduction in the donor binding energy. Supported be observations of a reduction in both the AlAs-like and InAs-like LO phonon frequencies and a broadening of the LO phonon line shape as the doping level is increased, the PL intensity also shows in increasing degrees at higher doping levels, a temperature dependence which is characteristic of disordered and amorphous materials.

Sub-bandgap refractive indexes and optical properties of Sidopedβ-Ga_(2)O_(3) semiconductor thin films

In this article,we present a theoretical study on the sub-bandgap refractive indexes and optical properties of Sidopedβ-Ga_(2)O_(3) thin films based on newly developed models.The measured sub-bandgap refractive indexes ofβ-Ga_(2)O_(3) thin film are explained well with the new model,leading to the determination of an explicit analytical dispersion of refractive indexes for photon energy below an effective optical bandgap energy of 4.952 eV for theβ-Ga_(2)O_(3) thin film.Then,the oscillatory structures in long wavelength regions in experimental transmission spectra of Si-dopedβ-Ga_(2)O_(3) thin films with different Si doping concentrations are quantitively interpreted utilizing the determined sub-bandgap refractive index dispersion.Meanwhile,effective optical bandgap values of Si-dopedβ-Ga_(2)O_(3) thin films are further determined and are found to decrease with increasing the Si doping concentration as expectedly.In addition,the sub-bandgap absorption coefficients of Si-dopedβ-Ga_(2)O_(3) thin film are calculated under the frame of the Franz–Keldysh mechanism due to the electric field effect of ionized Si impurities.The theoretical absorption coefficients agree with the available experimental data.These key parameters obtained in the present study may enrich the present understanding of the sub-bandgap refractive indexes and optical properties of impurity-dopedβ-Ga_(2)O_(3) thin films.

Nonlinear Doping, Chemical Passivation and Photoluminescence Mechanism in Water-Soluble Silicon Quantum Dots by Mechanochemical Synthesis

A series of boron- and phosphorus-doped silicon wafers are used to prepare a series of doped silicon nanocrystals （nc-Si） by high-energy ball milling with carboxylic acid-terminated surface. The sizes of the nc-Si samples are demonstrated to be 〈 S nm. The doping levels of the nc-Si are found to be nonlinearly dependent on the original doping level of the wafers by x-ray photoelectron spectroscopy measurement. It is found that the nonlinear doping process will lead to the nonlinear chemical passivation and photoluminescence （I3L） intensity evolution. The doping, chemical passivation and PL mechanisms of the doped nc-Si samples prepared by mechanochemical synthesis are analyzed in detail.