非掺杂型Si/SiGe异质结外延与表征

以自旋为编码单元的硅基半导体量子计算与传统微电子工艺兼容,易拓展且可以同位素纯化提高退相干时间,因而备受关注.本研究工作通过分子束外延生长了高质量非掺杂型Si/SiGe异质结并测试了二维电子气迁移率.球差电镜观察到原子级尖锐界面,原子力显微镜表征显示其表面均方根粗糙度仅为0.44 nm,低温下迁移率达到20.21×10^(4)cm^(2)·V^(–1)·s^(–1).不同栅压下载流子浓度和迁移率的幂指数为1.026,材料丁格比值在7—12之间,表明载流子主要受到背景杂质散射和半导体/氧化物的界面散射.

Mg元素含量对Al-2Si-0.8Fe合金抗退火软化和导电性能的影响

采用光学显微镜、扫描电镜、布氏硬度计、电子万能材料试验机和涡流导电仪等研究了Mg元素含量对Al-2Si-0.8Fe合金的微观组织、力学性能及导电性能的影响。结果表明:随着Mg元素含量的增加,铸态Al-2Si-0.8Fe合金的硬度和抗拉强度不断提高,而对其导电性能的影响相对较小;当Mg含量增至1.5%时,铸态合金的硬度和抗拉强度达到最大值,分别为77.1 HBW和190 MPa,较Al-2Si-0.8Fe合金的硬度(42.3 HBW)和抗拉强度(123.5 MPa)分别提升了82.3%和53.8%,而导电性能的下降幅度控制在2.9%以内。低温退火处理后,合金的导电率有所提升;当Mg含量超过1%时,退火态合金的硬度显著降低,出现退火软化现象;而在Mg含量低于1%时,退火态合金的抗拉强度和硬度并未明显下降,分别达到201.7 MPa和78 HBW,显示出良好的抗退火软化特性。添加少量的Mg后,合金的组织主要由初生α-Al、共晶Mg_(2)Si相以及长针状β-Al_(5)FeSi相构成,而随着Mg含量的增加,会发生β-Al_(5)FeSi→π-Al_8Mg_(3)FeSi_(6)反应,导致合金中Mg_(2)Si强化相数量减少,无法弥补铸态合金固溶强化对硬度的提升效果,从而产生退火软化现象。

Martensitic Transformation in Fe-Mn-Si Based Shape Memory Alloys

The critical driving force for martensitic transformation fcc ( gamma ) yields hcp ( epsilon ) in ternary Fe-Mn-Si alloys increases with the content of Mn and decreases with that of Si. Thermodynamical prediction of M//s in ternary Fe-Mn-Si alloys was established. The fcc ( gamma ) yields hcp ( epsilon ) martensitic transformation in Fe-Mn-Si is a semi-thermoelastic and the nucleation process does not strongly depend on soft mode. Nucleation occurs directly through an overlapping of stacking fault rather than pole mechanism, and it is suggested that stacking fault energy (SFE) is the main factor controlling nucleation. Based on the phenomenological theory of martensite crystallography, a shuffle on (0001)//h//c//p plane is required when d//1//1//1 does not equal d//0//0//0//2. The derived principal strain in Bain distortion is smaller, i, e., more reasonable than the values given by Christian. Alloying elements strengthening the austenite, lowering SFE of gamma phase and reducing T//N** gamma temperature may be beneficial to shape memory effect of Fe-Mn-Si based alloys. Accordingly, Fe-Mn-Si-RE and Fe-Mn-Si-Cr-N (or Fe-Mn-Si-Ni-Cr-N) are worthy to be recommended as shape memory materials with improved shape memory effect. (Edited author abstract) 48 Refs.

Oxidation and hot corrosion behaviors of Nb−Si based ultrahigh temperature alloys at 900℃

Oxidation and hot corrosion behaviors at 900 ℃ of Nb-Si based ultrahigh temperature alloys were investigated. Both oxidation and hot corrosion kinetics curves of the alloy involve an initial parabolic stage and a later rapid linear stage. In the initial oxidation stage(1-50 h), a thin and continuous scale is formed on the alloy surface, while severe pest degradation phenomenon is observed in the linear oxidation stage. Compared with oxidation of the alloy in static air, a linear hot corrosion stage happens earlier and catastrophic scale disintegration occurs after hot corrosion for 20-100 h, demonstrating that molten salts(Na2SO4 and NaCl) could significantly accelerate the oxidation process of the alloy. STEM results indicate that the corroded scale consists mainly of TiO2, Nb2O5, TiNb2O7, amorphous silicate and NaNbO3.

Weldability and Microstructure of Nickel-Silicon Based Alloys

The NiSix based alloy typically has poor weldability due to its lower ductility. A limited amount of work has been performed on the weldability of NiSix based alloys. Therefore, the effect of heat treatment and welding parameters on weldability of the alloys, and the relationship between the weldability and microstructure were studied. The results show that the as-cast Ni-Si-Nb-B alloy （Ni 76. 5%, Si 20%, Nb 3%, and B 0. 5%） could be successfully welded after preheating at 600 ℃. The welding procedure should be performed on the alloys before any heat treatment and a preheating at 600 ℃ should be used. The fusion zone is harder than the matrix due to a large amount of 7 phase and a finer microstructure. The cracks are predominantly intergranular in heat affected zone and associated with the needle-like ）, phase. The heat treatment before welding increases the tendency of cracking in the fusion zone.

Microstructure and texture evolution of Ti-Nb-Si based alloys for biomedical applications

Microstructure and texture of Ti-Nb-Si based alloys, prepared by water quenching from β-phase field, cold rolling and recrystallization heat treatment followed by water quenching, were investigated in terms of optical microstructure and analysis of X-ray pole figure result. In as-quenched sample, relatively random distribution of pole figure was detected without showing a specific texture component. In as-cold rolled sample, however, it is found well-developed several texture components consisting of rotated cube, α-fiber and γ-fiber texture components which are frequently observed in bcc-structured metals and alloys were found. Therefore, texture components developed in the present alloys are closely related to the deformation of β-phase even though small amount of α″ phase co-exist in the microstructure. In recrystallized sample, α-fiber texture component is weakly detected while the other texture components, rotated cube and γ-fiber components, appears to be relatively unchanged. No additional texture components were detected besides those texture components observed in the cold rolled samples.

Research on design and firing performance of Si-based detonator

For the chip integration of MEMS(micro-electromechanical system) safety and arming device, a miniature detonator needs to be developed to reduce the weight and volume of explosive train. A Si-based micro-detonator is designed and fabricated, which meets the requirement of MEMS safety and arming device. The firing sensitivity of micro-detonator is tested according to GJB/z377A-94 sensitivity test methods:Langlie. The function time of micro-detonator is measured using wire probe and photoelectric transducer. The result shows the average firing voltage is 6.4 V when the discharge capacitance of firing electro-circuit is 33 mF. And the average function time is 5.48 ms. The firing energy actually utilized by Si-based micro-detonator is explored.

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.

硅基SiC薄膜制备与应用研究进展

碳化硅(SiC)材料具有极为优良的物理、化学及电学性能,可满足在高温、高腐蚀等极端条件下的应用,碳化硅还是极端工作条件下微机电系统(MEMS)的主要候选材料,成为国际上新材料、微电子和光电子领域研究的热点。同时,碳化硅有与硅同属立方晶系的同质异形体,可与硅工艺技术相结合制备出适应大规模集成电路需要的硅基器件,因此用硅晶片作为衬底制备碳化硅薄膜的工作受到研究人员的特别重视。本文综述了近年来国内外硅基碳化硅薄膜的研究现状,就其制备方法进行了系统的介绍,主要包括各种化学气相沉积(Chemical vapor deposition,CVD)法和物理气相沉积(Physical vapor deposition,PVD)法,并归纳了对硅基碳化硅薄膜性能的研究,包括杨氏模量、硬度、薄膜反射率、透射率、发光性能、电阻、压阻、电阻率和电导率等,以及其在微机电系统传感器、生物传感器和太阳能电池等领域的应用,最后对硅基碳化硅薄膜未来的发展进行了展望。

Machine learning technique for prediction of magnetocaloric effect in La(Fe,Si/Al)_(13)-based materials

Data-mining techniques using machine learning are powerful and efficient for materials design, possessing great potential for discovering new materials with good characteristics. Here, this technique has been used on composition design for La（Fe,Si/Al）（13）-based materials, which are regarded as one of the most promising magnetic refrigerants in practice. Three prediction models are built by using a machine learning algorithm called gradient boosting regression tree（GBRT） to essentially find the correlation between the Curie temperature（TC）, maximum value of magnetic entropy change（（？SM）（max））,and chemical composition, all of which yield high accuracy in the prediction of TC and（？SM）（max）. The performance metric coefficient scores of determination（R^2） for the three models are 0.96, 0.87, and 0.91. These results suggest that all of the models are well-developed predictive models on the challenging issue of generalization ability for untrained data, which can not only provide us with suggestions for real experiments but also help us gain physical insights to find proper composition for further magnetic refrigeration applications.

EFFECT OF DYNAMIC RECRYSTALLIZATION ON SHAPE MEMORY EFFECT IN Fe－Mn－Si BASED ALLOYS

Improvement of shape, memory effect (SME) in Fe-Mn-Si based alloys has been investigated, compared with that by conventional 'training' treatment. It is found that SME in Fe-Mn-Si alloy can be greatly improved by ausforming and 3.8%recovery strain and 2.2% complete recovery strain can be reached by ausforming at 973 K when dynamic recrystallization has just occurred. The mechanism for the improvement of SME is proposed.

Microstructure Development of Directionally Solidified Nb-Ti-Si Based Ultrahigh Temperature Alloy

Integrally directional solidification of an Nb-Ti-Si based ultrahigh temperature alloy was performed in an ultrahigh temperature and high thermal gradient furnace with the use of ceramic crucibles. The microstructural evolution with the withdrawing rate increasing during directional solidification was revealed. The integrally directionally solidified microstructure was composed of couple grown lamellar (Nbss+(Nb,X)5Si3) eutectic colonies and a few hexagonally cross-sectioned (Nb,X)5Si3 columns (X represents Ti and Hf elements). All the directionally solidified microstructure was straightly aligned along the longitudinal axis of the specimens. With increasing of the withdrawing rate, the average diameter of the eutectic cells and inter lamella spacings in the eutectic cell decreased. The near-planar solid/liquid interface appeared when the withdrawing rate was 1μm/s, and the cellular solid/liquid interface formed when the withdrawing rate was 5 μm/s.

New Mg_2Si based Alloy for Automobile Engine Cylinder Liner

New Mg2Si based alloy were prepared by mechanical alloying. Sintering temperature was from 825 to 865K, which indicated that few Mg2Si were produced at lower temperature while MgO were produced at higher temperature. Microstructure image showed that at sintering temperature of 855K, Mg2Si were mostly synthesized with the reaction of purity magnesia powder and silicon powder. Hardness and wear tests proved that the new synthetic silicon magnesium alloy had higher hardness and good wear resistance. Under the same testing conditions, it is found that the hardness of the new material is 420.50, and pure magnesium is only 41.65.In the same experiments it is also found that under the same pressure, pure magnesium alloys than silicon wearing capacity of pure magnesium is 2 times as high that of Mg2Si based alloy. It shows that Mg2Si based alloy is the ideal material for the wear parts of car engine cylinder liner because of its small density, stable dimension, high hardness and wear-resisting.

Fabrication and Characterization of a Single Electron Transistor Based on a Silicon-on-Insulator

A single electron transistor based on a silicon-on-insulator is successfully fabricated with electron-beam nano- lithography, inductively coupled plasma etching, thermal oxidation and other techniques. The unique design of the pattern inversion is used, and the pattern is transferred to be negative in the electron-beam lithography step. The oxidation process is used to form the silicon oxide tunneling barriers, and to further reduce the effective size of the quantum dot. Combinations of these methods offer advantages of good size controllability and accuracy, high reproducibility, low cost, large-area contacts, allowing batch fabrication of single electron transistors and good integration with a radio-frequency tank circuit. The fabricated single electron transistor with a quantum dot about 50nto in diameter is demonstrated to operate at temperatures up to 70K. The charging energy of the Coulomb island is about 12.5meV.

Effect of Si content on mechanical properties of Nb-Si based alloys with Nb_(ss)/ Nb_5Si_3 structure

In Nb-Si based alloys with a two-phase Nbss/ intermetallic Nb5Si3 structure, the Nb5Si3 provides high-temperature strength, while the Nb solid-solution phase, Nbss, contributes to room-temperature ductility and toughness. The results show that in Nb-15W-10Hf-xSi alloys (x= 0.5, 5 and 18, mole fraction, %), the volume fraction of the Nb5Si3 is 0 for the 0.5% Si sample, 15% for the 5% Si sample and the 50% for 18% Si sample. With increasing Si content, i.e., the Nb5Si3 fraction, the high-temperature strength is improved considerably, but room-temperature ductility and toughness are degraded. For the sample Nb-15W-10Hf-18Si with 50% Nb5Si3, the compressive strength at 1 500℃and the room-temperature fracture toughness are 500 MPa and 6.8 MPa·m1/2, respectively, those for the Nb5Si3 free sample, Nb-15W-10Hf-0.5Si, are 190 MPa and 13.6 MPa·m1/2.

SYNTHESIS OF ORGANOMETALLIC PRECURSORS FOR Si/Zr/C/N-BASED CERAMICS

A new kind of organometallic precursor for Si/Zr/C/N-based ceramics was synthesized from the amine exchangereaction of hexamethylcyclotrisilazane (D_3~N) and tetrakis(diethylamino) zirconium (Zr[NEt_2]_4). Pyrolysis was performedunder nitrogen at 800℃ in a tube furnace equipped with a temperature program controller. The highest pyrolytic yield was67.5%.

Effect of Sr on forming properties of Al-Mg-Si based alloy sheets

The effects of Sr element on the forming properties of the Al-Mg-Si based alloy sheets were studied by tensile test, metallograph, DSC, XRD, SEM and TEM. The results show that the tensile strength of aluminum alloy sheet added 0.033%(mass fraction)Sr increases comparing with that of free Sr. Simultaneously, the forming properties of sheets evidently increase, the elongation hardenability (n) and plastic strain ratio (r) and Erichsen number increase 27.8%, 11.1%, 10.8% and 12%, respectively, and the forming limit diagram increases evidently, too. The analysis shows that Sr is surface active element, which can refine grains of alloys, promote precipitation, reduce activation energy ofβ' phase, and lead the formation ofα-(Al8Fe2Si) phase instead ofβ-(Al5FeSi) phase. As a result, the forming properties of the alloy sheet increase.

The n-type Si-based materials applied on the front surface of IBC-SHJ solar cells

Interdigitated back contact silicon hetero-junction(IBC-SHJ) solar cells exhibit excellent performance owing to the IBC and SHJ structures.The front surface field(FSF) layer composed of electric field passivation and chemical passivation has been proved to play an important role in IBC-SHJ solar cells.The electric field passivated layer n^+-a-Si: H, an n-type Si alloy with carbon or oxygen in amorphous phase, is simulated in this study to investigate its effect on IBC-SHJ.It is indicated that the n^+-a-Si: H layer with wider band gap can reduce the light absorption on the front side efficaciously,which hinders the surface recombination of photo-generated carriers and thus contributes to the improvement of the short circuit current density Jsc.The highly doped n^+-a-Si: H can result in the remakable energy band bending, which makes it outstanding in the field passivation, while it makes little contribution to the chemical passivation.It is noteworthy that when the electric field intensity exceeds 1.3 × 10^5 V/cm, the efficiency decrease caused by the inferior chemical passivation is only 0.16%.In this study, the IBC-SHJ solar cell with a front n^+-a-Si: H field passivation layer is simulated, which shows the high efficiency of 26% in spite of the inferior chemical passivation on the front surface.

Martensitic transformation and shape memory effect in ausaged Fe-Ni-Si-based alloys

It is well known that the morphologies of the α’ martensite formed from the γ phase in ferrous alloys are classified into five types of lath, butterfly, （225）A type plate,lenticular and thin-plate. Among those α’ martensites, only the thin-plate martensite,which is characterized by containing a high density of transformation twins, has a potential of exhibiting a perfect shape memory （SM） effect.Recently the present authors found in Fe-Ni-Si alloys that the thin-plate martensite is formed by the introduction of fine and coherent γ’-（Ni,Fe）3Si particles with a L12 ordered structure in the austenite matrix due to ausaging. In the present study, the SM properties of the ausaged Fe-Ni-Si alloys with the thin-plate martensite are investigated by a conventional bending-test. The effects of the addition of Co to the Fe-Ni-Si alloys on the martensitic transformation and the SM properties are also investigated. It is shown that while the ausaged Fe-Ni-Si ternary alloys exhibit an imperfect SM effect due to reverse transformation from stress-induced thin-plate martensite to austenite, the SM properties are improved by the addition of Co. An almost perfect SM effect is confirmed in the Fe-Ni-Si-Co alloys by heating to 1 100 ℃ after deformation at -196 ℃.

低成本Si基GaN微电子学的新进展(续)

进入21世纪后,宽禁带半导体GaN微电子学发展迅速,SiC基GaN微电子学已成为微波电子学的发展主流,且正在向更高频率和更高功率密度的新一代GaN微波功率器件发展。为了降低成本,Si基GaN微电子学应运而生,在5G通信、电动汽车等绿色能源应用发展的带动下,Si基GaN微电子学已进入产业化快速发展阶段。介绍了Si基GaN微电子学在射频Si基GaN高电子迁移率晶体管(HEMT)新器件结构、工艺与可靠性,Si基GaN HEMT单片微波集成电路(MMIC),Si基E模功率GaN HEMT结构设计,大尺寸Si基GaN HEMT工艺,Si基GaN功率开关器件的可靠性,Si基GaN功率变换器的单片集成和高频开关Si基GaN器件的应用创新等工程化、产业化方面的最新技术进展。分析和评价了低成本Si基GaN微电子学工程化和产业化的发展态势。