硅纳米线拉伸与熔化行为的原子模拟

Molecular dynamics simulations with Stillinger-Weber potential are used to study the tensile and melting behavior of single-crystalline silicon nanowires（SiNWs）.The tensile tests show that the tensile behavior of the SiNWs is strongly dependent on the simulation temperature,the strain rate,and the diameter of the nanowires.For a given diameter,the critical load significantly decreases as the temperature increases and also as the strain rate decreases.Additionally,the critical load increases as the diameter increases.Moreover,the melting tests demonstrate that both melting temperature and melting heat of the SiNWs decrease with decreasing diameter and length,due to the increase in surface energy.The melting process of SiNWs with increasing temperature is also investigated.     

硅纳米线的固-液-固热生长及升温特性研究

该文报道一种直接在硅片上热生长硅纳米线的新方法。与传统的VLS生长机制不同,该方法在生长硅纳米线的过程中没有引入任何气态或液态硅源.是一种全新的固液固(SLS)生长机制。实验中使用了Ni,Au等金属作为催化剂,由Ar,H2等作为载流气体.系统压强为2.5104Pa,生长温度为950-1000℃.生长出的硅纳米线表面光滑,呈纯非晶态,直径为10-40 nm,长度可达数十微米,升温特性对硅纳米线SLS热生长起重要作用。研究了各项实验参数(包括气氛压强,加热温度及加热时间等)对硅纳米线生长的影响。     

The aligned Si nanowires growth using MW plasma enhanced CVD

New and simple modification of vapor-liquid-solid process for Si nanowires growth based on microwave plasma enhanced chemical vapor deposition that uses solid-state Si target as a source of Si atoms was developed. The method was temperature and pressure controlled evaporation of solid phase of Si source in hydrogen microwave plasma. Aligned growth of Si nanowires was performed in local electric field by applying of constant negative bias to substrate holder. Deposited Si nanowires were studied by scanning electron microscopy (SEM), Raman and photoluminescence spectroscopy. Correlation between photoluminescence spectra and Si nanowires properties were studied.     

Uniaxial, tensile-strained Si devices

Uniaxial, in-plane, tensile straining of silicon devices is reported. Strain is applied via mechanical techniques and then fixed by bonding to an appropriate substrate. Results are reported for diffused resistors and for some metal-oxide semiconductor field effect transistor (MOSFET) devices. Strain is introduced after device processing is complete, which enables full advantage to be taken of mainstream silicon processing technology. This macroscopic method is effective regardless of device size but has particular benefit in the deep submicron region. Mobility conductivity enhancement factors >2 for an applied strain of 0.05% are reported.     

The mechanical behavior of silicon during small-scale indentation

The mechanical behavior of crystalline silicon during small-scale indentation has been studied using a Nanoindenter. Tests were performed on bothp-type andn-type materials in the (100), (110), and (111) orientations at peak loads ranging from 0.5 to 120 mN. The indentation load-displacement curves exhibit two features which appear to be unique to silicon. First, at large peak loads, a sharp discontinuity in displacement is observed as the indenter is unloaded. Second, at small peak loads, a large, non-degenerative hysteresis is exhibited. Possible mechanistic origins for the discontinuity and hysteresis are discussed.     

“Y”型、竹节型与直纳米碳管的力学特性研究

采用基于BrennerREAO(reactiveempiricalbondorder)势的分子动力学方法,模拟了“Y”型、竹节型与直纳米碳管的拉伸过程。结合有限元分析,对比并讨论了“Y”型、竹节型纳米碳管与直纳米碳管拉伸力学性能的差异。研究结果表明,拉伸“Y”型、竹节型纳米碳管的屈服与断裂均发生在其粗管与细管过渡的“应力集中”部位;“应力集中”致使“Y”型、竹节型纳米碳管的抗拉强度与韧性明显低于直纳米碳管;然而,“Y”型、竹节型碳管的弹性模量依然与直纳米碳管相当。     

Ⅲ–Ⅴ ternary nanowires on Si substrates: growth,characterization and device applications

Over the past decades, the progress in the growth of materials which can be applied to cutting-edge technologies in the field of electronics, optoelectronics and energy harvesting has been remarkable. Among the various materials, group Ⅲ–Ⅴ semiconductors are of particular interest and have been widely investigated due to their excellent optical properties and high carrier mobility. However, the integration of Ⅲ–Ⅴ structures as light sources and numerous other optical components on Si,which is the foundation for most optoelectronic and electronic integrated circuits, has been hindered by the large lattice mismatch between these compounds. This mismatch results in substantial amounts of strain and degradation of the performance of the devices. Nanowires(NWs) are unique nanostructures that induce elastic strain relaxation, allowing for the monolithic integration of Ⅲ–Ⅴ semiconductors on the cheap and mature Si platform. A technique that ensures flexibility and freedom in the design of NW structures is the growth of ternary Ⅲ–Ⅴ NWs, which offer a tuneable frame of optical characteristics, merely by adjusting their nominal composition. In this review, we will focus on the recent progress in the growth of ternary Ⅲ–Ⅴ NWs on Si substrates. After analysing the growth mechanisms that are being employed and describing the effect of strain in the NW growth, we will thoroughly inspect the available literature and present the growth methods, characterization and optical measurements of each of the Ⅲ–Ⅴ ternary alloys that have been demonstrated. The different properties and special treatments required for each of these material platforms are also discussed. Moreover, we will present the results from the works on device fabrication, including lasers, solar cells, water splitting devices, photodetectors and FETs, where ternary Ⅲ–Ⅴ NWs were used as building blocks. Through the current paper, we exhibit the up-to-date state in this field of research and summarize the important accomplishments of the past few years.     

III–V ternary nanowires on Si substrates: growth,characterization and device applications

Over the past decades, the progress in the growth of materials which can be applied to cutting-edge technologies in the field of electronics, optoelectronics and energy harvesting has been remarkable. Among the various materials, group III–V semiconductors are of particular interest and have been widely investigated due to their excellent optical properties and high carrier mobility. However, the integration of III–V structures as light sources and numerous other optical components on Si, which is the foundation for most optoelectronic and electronic integrated circuits, has been hindered by the large lattice mismatch between these compounds. This mismatch results in substantial amounts of strain and degradation of the performance of the devices. Nanowires (NWs) are unique nanostructures that induce elastic strain relaxation, allowing for the monolithic integration of III–V semiconductors on the cheap and mature Si platform. A technique that ensures flexibility and freedom in the design of NW structures is the growth of ternary III–V NWs, which offer a tuneable frame of optical characteristics, merely by adjusting their nominal composition. In this review, we will focus on the recent progress in the growth of ternary III–V NWs on Si substrates. After analysing the growth mechanisms that are being employed and describing the effect of strain in the NW growth, we will thoroughly inspect the available literature and present the growth methods, characterization and optical measurements of each of the III–V ternary alloys that have been demonstrated. The different properties and special treatments required for each of these material platforms are also discussed. Moreover, we will present the results from the works on device fabrication, including lasers, solar cells, water splitting devices, photodetectors and FETs, where ternary III–V NWs were used as building blocks. Through the current paper, we exhibit the up-to-date state in this field of research and summarize the important accomplishments of the past few years.     

P型张应变Si/SiGe量子阱红外探测器的能带设计

提出P型张应变Si/SiGe量子阱红外探测器(QWIP)结构,应用k·P方法计算应变Si/SiGe量子阱价带能带结构和应变SiGe合金空穴有效质量.结果表明量子阱中引入张应变使轻重空穴反转,基态为有效质量较小的轻空穴态,因此P型张应变Si/SiGe QWIP与n型QWIP相比具有更低的暗电流;而与P型压应变或无应变QWIP相比光吸收和载流子输运特性具有较好改善.在此基础上讨论了束缚态到准束缚态子带跃迁型张应变p-Si/SiGe QWIP的优化设计.     

P型张应变Si/SiGe量子阱红外探测器的能带设计

提出P型张应变Si/SiGe量子阱红外探测器(QWIP)结构,应用k·P方法计算应变Si/SiGe量子阱价带能带结构和应变SiGe合金空穴有效质量.结果表明量子阱中引入张应变使轻重空穴反转,基态为有效质量较小的轻空穴态,因此P型张应变Si/SiGe QWIP与n型QWIP相比具有更低的暗电流;而与P型压应变或无应变QWIP相比光吸收和载流子输运特性具有较好改善.在此基础上讨论了束缚态到准束缚态子带跃迁型张应变p-Si/SiGe QWIP的优化设计.     

MBE-Grown Cubic ZnS Nanowires

Ultrathin ZnS nanowires (NWs) were grown on a sapphire (0001) substrate at 430°C by the molecular-beam epitaxy (MBE) technique using self-assembled Au droplets as the catalyst. It was found that these NWs mainly consist of the cubic phase but a small portion was in the hexagonal phase. The analysis of the temperature-dependent band-edge (BE) emission of these NWs and that of a ZnS thin film revealed that the energy shift of the interband transition on temperature in ZnS is mainly attributed to the electron–phonon interactions. The observed blue shift of the BE emission of ZnS NWs could be quantitatively explained by the confinement of the excited excitons in the NW geometry.     

表面封装用无铅软钎料的接头强度及熔点范围的研究

研究了Bi的添加量,对电子表面封装(SMT)用Sn-Ag近共晶无铅软钎料钎焊接头抗拉强度和熔点及熔点范围的影响。随着Bi含量的增加,钎焊接头抗拉强度也随着增加,同时钎料的液固相线温度均降低。当Bi的含量达到5%时,抗拉强度增加快;Bi的添加量大于5%时,抗拉强度上升缓慢。在Bi的含量增加时,熔点温度范围也逐渐变宽,使得凝固时间变长,这对于表面组装中的电子元件与器件的焊接是非常不利的。故在Sn-Ag近共晶无铅软钎料中Bi的添加量,应加以适当的控制。     

张应变锗薄膜制备技术的研究进展

由于与硅集成电路工艺兼容的张应变锗薄膜在光电器件如光电探测器、调制器,特别是发光器件中具有潜在的应用前景,使其得到了广泛关注.然而,在锗薄膜中引入可控的、大的张应变是个挑战.综述了张应变锗薄膜制备技术的研究进展,重点介绍了在锗薄膜中引入张应变的外延技术、应变转移技术、应变浓缩技术和机械应变技术的工艺流程和实验结果,并讨论了它们的优点和缺点.采用应变浓缩技术制备的厚度为350 nm的锗薄膜微桥的单轴张应变和微盘的双轴张应变分别达到了4.9％和1.9％,可将锗调制为直接带隙材料,适用于锗激光器的研制.     

Effect of Lattice Mismatch on Luminescence of ZnO/Si Hetero-Structure

研究了ZnO薄膜中应力对发光的影响.实验样品为ZnO体单晶、在Si基片上直接生长的ZnO薄膜以及通过SiC过渡层在Si基片上生长的ZnO薄膜.测量了这三种样品的X射线衍射图形、喇曼光谱和光致发光光谱.由X射线衍射图形可以看出,由于SiC过渡层缓解了ZnO与Si之间的晶格失配,使得通过SiC过渡层在Si上生长的ZnO薄膜的结晶质量好于直接在Si上生长的ZnO薄膜的质量.进一步通过喇曼谱测量发现,与ZnO体单晶相比,直接在Si上生长的ZnO薄膜的E2(high)峰红移1.9cm-1,根据喇曼谱峰位移与应力的关系可以推出薄膜中存在0.4GPa的张应力;而通过SiC过渡层在Si上生长的ZnO薄膜的E2(high)峰红移0.9cm-1,对应着0.2GPa的张应力.对照X射线衍射图形的结果可以看出,薄膜中张应力的大小与薄膜的结晶质量密切相关,表明张应力来源于外延层和基片间的晶格失配,晶格失配越大,外延层中产生的张应力越大.有无SiC过渡层的两种薄膜样品的PL光谱中都存在紫外和绿光两种谱带,随样品热处理时氧气分压增加,两种样品都出现绿光增强的相似的变化规律,但有SiC过渡层的样品的变化幅度较小.这一结果说明,绿色发光中心与薄膜的质量,也就是与薄膜中存在的张应力大小有关.在以往研究中得出的非故意掺杂ZnO薄膜的绿色发光中心来源于氧反位缺陷(Ozn),文中研究的结果正好可以解释氧反位缺陷形成的原因.由于薄膜中存在张应力,使得样品的能量升高,其结果必然会产生缺陷来释放张应力,以便降低系统能量.而氧离子半径大于锌离子半径,氧替位锌有利于释放张应力,也就是说,在存在张应力的情况下,Ozn的形成能降低.这一结果进一步证明Si上生长的ZnO薄膜中的绿色发光中心与氧反位缺陷有关.