化学气相沉积法碳化硅外延设备技术进展

碳化硅(SiC)是制作高温、高频、大功率电子器件的理想电子材料,近20年来随着外延设备和工艺技术水平不断提升,外延膜生长速率和品质逐步提高,碳化硅在新能源汽车、光伏产业、高压输配线和智能电站等领域的应用需求越来越大。与硅半导体产业不同,碳化硅器件必须在外延膜上进行加工,因此碳化硅外延设备在整个产业链中占据承上启下的重要位置,而且也是整个产业链中最复杂、最难开发的设备。本文从碳化硅外延生长机理出发,结合反应室设计和材料科学的发展,介绍了化学气相沉积(CVD)法碳化硅外延设备反应室、加热系统和旋转系统等的技术进展,最后分析了CVD法碳化硅外延设备未来的研究重点和发展方向。     

石墨烯及其纳米复合材料的制备与应用研究

石墨烯作为一种新兴二维碳纳米材料,具有完美的晶体结构和诸多优异的物理化学性能.石墨烯独特的电学、热学、光学和力学性能,使其在电子器件、导热材料、气体传感器、感光元件以及环境科学等领域具有广阔的应用前景.其潜在的实际应用价值,使石墨烯材料的开发成为当前最受关注的研究热点之一.本文从石墨烯的来源、结构、分类和基本性质出发,概述了石墨烯及其衍生物的制备方法及属性特征,进而介绍了石墨烯及其衍生物纳米复合材料在电子、材料、储能和环境等领域中的最新研究进展,并对石墨烯及其纳米复合材料的发展前景进行了展望.     

新型二维铜族硫族化合物的研究进展

二维材料因其纳米级尺寸、超凡的电子特性、出色的机械性能等,被视为下一代信息器件的理想材料。随着外延生长等自下而上制备方法以及材料计算方法的发展和提高,越来越多的体相非层状的二维材料被制备和发现。近年来在信息器件等领域具有应用潜力的体相非层状的二维铜族(11族)硫族化合物得到广泛关注,铜族元素位于化学元素周期表中的11族,主要包括铜、银和金等元素。本文综述了二维铜族硫族化合物的研究进展,以化学计量比为主线,将二维铜族硫族化合物分为MX单层(M=Cu,Ag,Au;X=O,S,Se,Te)、M₂X单层以及其他化学计量比的铜族硫族化合物单层。从实验合成和理论模拟两个角度出发,对二维铜族硫族化合物原子结构、能带结构、电学特性等进行介绍。从现有的报道来看,体相非层状的新型二维铜族硫族化合物不仅包含半导体、金属等电子性质,还表现出拓扑、磁性等丰富的新奇物性,是一类值得关注的新型二维功能材料。     

Germanium: Epitaxy and its applications

This paper reviews the most important properties of germanium, gives an insight into the newer techniques and technology for the growth of epitaxial Ge thin layers and focuses on some applications of this material, with a special emphasis on recent achievements in electronics and photovoltaics. We will highlight the recent development of Ge research and will give an account of the most important Ge applications that emerged in the last two decades.Germanium is a key material in modern material science and society: it is used as a dopant in fiber optic glasses and in semiconductor devices, both in activating conduction in layers and also as a substrate for III–V epitaxy. Ge is also widely used in infrared (IR) detection and imaging and as a polymerization catalyst for polyethylene terephthalate (PET). Moreover, high-speed electronics for cell phone communications relies heavily on SiGe alloys. Ge electronics is nowadays gaining new interest because of the enhanced electronic properties of this material compared to standard silicon devices, but the lack of a suitable gate oxide still limits its development. High efficiency solar cells, mainly for space use but also for terrestrial solar concentration have surpassed 40% efficiency and Ge has a lead role in achieving this goal.The main focus of the paper is on Ge epitaxy. Since epitaxy starts from the surface of the substrate, different studies on substrate pre-epitaxy, surface analysis and preparations are reviewed, covering the most common substrates for Ge deposition such as Ge, Si and GaAs. The most used Ge precursors such as GeH₄ and GeCl₄ are described, but several novel precursors, mostly metal-organic, have recently been developed and are becoming more common in epitaxial Ge deposition. Epitaxial growth of Ge by means of the most common methods, including Chemical Vapour Deposition and Molecular Beam Epitaxy is discussed, along with some recent advances in Ge deposition, such as Atomic Layer Deposition and Low Energy Plasma-Enhanced Chemical Vapour Deposition.Several Ge applications are finally discussed, with the aim of providing insights into the potential of this material for the development of novel devices that are able to surpass the current limits of standard device design. Ge in microelectronics is becoming more and more important, thanks to the possibilities offered by bandgap engineering of strained SiGe/Si. However, lack of a good Ge oxide is posing several problems in device improvement. In the field of photovoltaics Ge is mainly used as a substrate for high efficiency III–V solar cells and for the development of thermophotovoltaic devices instead of the most expensive and scarcer GaSb. In this field, Ge epitaxy is very rare but the development of an epitaxial Ge process may help in developing new solar cells concepts and to improve the efficiency of thermophotovoltaic converters. Ge may play a role even in new spintronics devices, since a GeMn alloy was found to have a higher Curie temperature than GaAsMn.     

高温溶液法生长SiC单晶的研究进展

碳化硅(SiC)作为第三代半导体材料,不仅禁带宽度较大,还兼具热导率高、饱和电子漂移速率高、抗辐射性能强、热稳定性和化学稳定性好等优良特性,在高温、高频、高功率电力电子器件和射频器件中有很好的应用潜力。高质量、大尺寸、低成本SiC单晶衬底的制备是实现SiC器件大规模应用的前提。受技术与工艺水平限制,目前SiC单晶衬底供应仍面临缺陷密度高、成品率低和成本高等问题。高温溶液生长(high temperature solution growth, HTSG)法生长SiC单晶具有晶体结晶质量高、易扩径、易实现p型掺杂等独特的优势,有望成为大规模量产SiC单晶的主要方法之一,目前该方法的主流技术模式是顶部籽晶溶液生长(top seeded solution growth, TSSG)法。本文首先回顾总结了TSSG法生长SiC单晶的发展历程,接着介绍和分析了该方法的基本原理和生长过程,然后从晶体生长热力学和动力学两方面总结了该方法的研究进展,并归纳了该方法的优势,最后分析了TSSG法生长SiC单晶技术在未来的研究重点和发展方向。     

Investigation of carrier scattering mechanisms in molybdenum diselenide single crystals by hall effect measurements

Molybdenum diselenide (MoSe₂) belong to the large family of layered transition metal dichalcogenides. It consists of weakly coupled sandwiched layers i.e. Se – Mo – Se in which a Mo atom layer is enclosed within two Se layers. This structure makes MoSe₂ extremely anisotropic in character and leads to unusual structural properties. In addition, MoSe₂ possess flexible nature along with good carrier mobility to make them potential candidate for fabricating flexible high mobility electronic devices such as Schottky barrier devices, FETs, solar cell etc. In context of this authors made an effort to study the low temperature (12 < T < 300 K) electronic transport properties of Molybdenum diselenide (MoSe₂). Through the investigation the temperature dependent Hall mobility study revealed that the grown crystals of MoSe₂possess a mixed scattering mechanism. It has been found that observed temperature dependant mobility has at least two transitions from lattice to impurity scatterings showing an imprint of multicarrier nature of this semiconductor originating from its complex band structure. It has been observed that the studied crystals have at least two group of carriers of differing origins in which transition between dominant scattering mechanisms occur at different temperatures. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

人造金刚石单晶薄膜的制备及表面形貌优化

人造金刚石作为一种高效的热管理衬底,在宽禁带半导体电子器件领域具有广泛的应用前景。然而微波等离子体化学气相沉积(MPCVD)法外延金刚石单晶的生长速率慢,表面粗糙度高,难以满足半导体器件的衬底需求。对此,本文采用MPCVD法制备金刚石单晶薄膜,通过分阶段生长监控样品的生长速率,结合显微镜照片和AFM表征样品的表面形貌和表面粗糙度,根据拉曼光谱和XRD分析外延薄膜的晶体质量,最终采用高/低甲烷浓度的两步法外延工艺,实现了金刚石单晶薄膜的高速外延,生长速率达到20 μm/h,同时获得了较为平整的表面形貌。本文所研究的甲烷调制两步法外延工艺能够起到表面形貌优化的作用,有利于在后续的相关器件研发中提供平整的金刚石衬底,推动高功率电子器件的发展。     

Crystal Structure Analysis at Normal and Low Temperature Conditions

80 years after its discovery X-ray diffraction presents itself as an outstanding method in structure determination which allows the most safe and accurate geometrical data of chemical structures to obtain compared to most other experimental methods. The major innovations in the recent past and the present state of crystal structure analysis are described together with some examples in inorganic and organic chemistry, including the use of synchrotron radiation. A variety of additional applications can be considered if the diffraction experiment is executed at low temperatures. Nitrogen gas stream devices and closed cycle helium cryostats are compared and their advantages/disadvantages are discussed. Finally some applications such as low temperature crystallization, temperature dependent structure analysis down to 20 K and deformation density work are illustrated.     

Semiconductor materials: Perspectives of optoelectronic integration in integrated optics

Semiconductor materials offer great potential for the combination of optical and electronic devices into single monolithic integrated structures. Aluminium-Gallium-Arsenide is the semiconductor material in which all major functions for such integration have been demonstrated, namely generation, guiding, coupling, modulation and detection of light as well as electronic circuit functions. This material forms the basis of the light emitting diodes and the lasers which made the first generation of optical fiber communication in the 0.8 to 0.9 μm range a success. With interest shifting to longer wavelengths between 1.3 and 1.6 μm where optical fiber losses are minimal, light sources and detectors are being developed in III–V compounds and corresponding integrated optics technology is expected to be forthcoming.Integrated optoelectronics has progressed to the stage where optical and electronic components like lasers, drivers and monitors or detectors and receivers are being integrated. Efforts in materials preparation and device processing will make optoelectronic systems which will handle and transmit optical and electronic signals a reality.     

Quantum dot nanostructures and molecular beam epitaxy

In order to fulfil the requirements of the information society there is a growing demand for nanoelectronic devices with new or largely improved performances; these devices are based on low-dimensional carrier systems, and in particular on zero-dimensional ones, that have peculiar properties as compared to the three- and two-dimensional counterparts.

In this paper we review and discuss the basic features of the Molecular Beam Epitaxy growth of quantum dots that are very interesting archetypes of zero-dimensional nanostructures; quantum dots can be obtained by the three-dimensional growth of self-assembled nanoislands that takes place during the preparation of structures based on highly lattice-mismatched materials. Aspects of the morphological, electronic and optical properties of quantum dots will be reviewed and it will be shown how the energy of confined levels for carriers is determined by design and growth parameters of nanostructures and how quantum dot emission wavelengths can be tuned in the windows of optoelectronic and photonic interest, such as that at 0.98, 1.31 and 1.55 μm. An overview of quantum dot devices will be given, with particular attention paid to the quantum dot laser, unarguably the most important application of quantum dots so far.     

Growth and characterization of two-dimensional crystals for communication and energy applications

This review article covers the growth and characterization of two-dimensional (2D) crystals of transition metal chalcogenides, h-BN, graphene, etc. The chemical vapor transport method for bulk single crystal growth is discussed in detail. Top-down methods like mechanical and liquid exfoliation and bottom-up methods like chemical vapor deposition and molecular beam epitaxy for mono/few-layer growth are described. The optimal characterization techniques such as optical, atomic force, scanning electron, and Raman spectroscopy for identification of mono/few-layer(s) of the 2D crystals are discussed. In addition, a survey was done for the application of 2D crystals for both creation and deterministic transfer of single-photon sources and photovoltaic systems. Finally, the application of plasmonic nanoantenna was proposed for enhanced solar-to-electrical energy conversion and faster/brighter quantum communication devices.     

单晶金刚石p型和n型掺杂的研究

超宽禁带半导体材料金刚石在热导率、载流子迁移率和击穿场强等方面表现出优异的性质,在功率电子学领域具有广阔的应用前景。实现p型和n型导电是制备金刚石半导体器件的基础要求,其中p型金刚石的发展较为成熟,主流的掺杂元素是硼,但在高掺杂时存在空穴迁移率迅速下降的问题;n型金刚石目前主流的掺杂元素是磷,还存在杂质能级深、电离能较大的问题,以及掺杂之后金刚石晶体中的缺陷造成载流子浓度和迁移率都比较低,电阻率难以达到器件的要求。因此制备高质量的p型和n型金刚石成为研究者关注的焦点。本文主要介绍金刚石独特的物理性质,概述化学气相沉积法和离子注入法实现金刚石掺杂的基本原理和参数指标,进而回顾两种方法进行单晶金刚石薄膜p型和n型掺杂的研究进展,系统总结了其面临的问题并对未来方向进行了展望。     

Vapour phase growth of epitaxial silicon carbide layers

After a brief overview of different epitaxial layer growth techniques, the homoepitaxial chemical vapour deposition (CVD) of SiC with a focus on hot-wall CVD is reviewed. Step-controlled epitaxy and site competition epitaxy have been utilized to grow polytype stable layers more than 50 μm in thickness and of high purity and crystalline perfection for power devices. The influence of growth parameters including gas flow, C/Si ratio, growth temperature and pressure on growth rate and layer uniformity in thickness and doping are discussed. Background doping levels as low as 10¹⁴ cm⁻³ have been achieved as well as layers doped over a wide n-type (nitrogen) and p-type (aluminium) range.

Furthermore the status of numerical process simulation is mentioned and SiC substrate preparation is described. In order to get flat and damage free epi-ready surfaces, they are prepared by different methods and characterised by atomic force microscopy and by scanning electron microscope using channelling patterns. For the investigation of defects in SiC high purity CVD layers are grown. The improvement of the quality of bulk crystal substrates by micropipe healing and so-called dislocation stop layers can further decrease the defect density and thus increase the yield and performance of devices. Due to its high growth rate functionality and scope for the use of multi-wafer equipment hot-wall CVD has become a well-established method in SiC-technology and has therefore great industrial potential.     

氮化镓功率电子器件封装技术研究进展

氮化镓(GaN)高电子迁移率晶体管(high electron mobility transistor, HEMT)以其击穿场强高、导通电阻低、转换效率高等特点引起科研人员的广泛关注并有望应用于电力电子系统中,但其高功率密度和高频特性给封装技术带来极大挑战。传统硅基电力电子器件封装中寄生电感参数较大,会引起开关振荡等问题,使GaN的优良性能难以充分发挥;另外,封装的热管理能力决定了功率器件的可靠性,若不能很好地解决器件的自热效应,会导致其性能降低,甚至芯片烧毁。本文在阐释传统封装技术应用于氮化镓功率电子器件时产生的开关震荡和热管理问题基础上,详细综述了针对以上问题进行的GaN封装技术研究进展,包括通过优化控制电路、减小电感L_g、提高电阻R_g抑制dv/dt、在栅电极上加入铁氧体磁环、优化PCB布局、提高磁通抵消量等方法解决寄生电感导致的开关振荡、高导热材料金刚石在器件热管理中的应用、器件封装结构改进,以及其他散热技术等。     

X‐Ray Diffuse Scattering on Self‐Organized Mesoscopic Structures

We highlight the great potential of x‐ray diffuse scattering for the characterization of mesoscopic structures. The mesoscopic length scale plays a fundamental role at semiconductors, since structures with spatial dimensions in the nanometer regime exhibit quantum size effects. Also the driving forces during epitaxial growth of these structures are most relevant at mesoscopic length scales and they may lead to self‐organization processes in that structures can form spontaneously during epitaxial growth. One of the most interesting features are quantum dots (QDs) since they exhibit zero‐dimensional electronic properties and thus show an impressive potential for applications in optoelectronic devices. X‐ray diffuse scattering is an excellent tool to investigate shape, size, and positional correlation and to characterize the strain field inside and in the vicinity of such self‐organized mesoscopic structures. It provides non‐destructive structural information over the entire mesoscopic length scale. X‐ray scattering is complementary to direct imaging techniques in that it gives a statistical average over large ensembles with high strain sensitivity. The application of different scattering techniques for the structural characterization of mesoscopic structures will be demonstrated. For the example of SiGe islands on Si (001) substrate it will be shown that x‐ray diffuse scattering is able to reveal details of germanium distribution in such islands. In a second example the investigation of the asymmetric shape and size of InP QDs that are grown on (001) In_0.48Ga_0.52 P/GaAs is described. The influence of positional correlation on the diffuse scattering will be discussed.     

有机电致发光器件(OLED)的制备方法和工艺

有机发光器件经过40年的发展,特别是在近年,具有理想特性的有机电致发光器件(OLED)成为研究开发的热点.由于OLED具有超轻薄、低成本、低功耗、宽视角、全固化、自发光、驱动电压低(3～12V) 及可实现柔软显示等诸多突出的性能,OLED将成为很有前途的新一代的平板显示技术.本文首先回顾了有机电致发光显示器件的发展历史,对有机材料、发展现状和趋势等都做了简要的概括.然后对当前先进的OLED器件结构、显示的发光机理,特别是对实现全彩显示的方法及制备工艺进行了详细的描述.     

Growth, characterization and modeling of alternating-current thin-film electroluminescent devices

This article seeks to put together the most important and updated information and to present a unified, systematic and concise overview of the classification, physical principles and methods of the ACTFEL device growth, characterization and modeling. The review takes a comprehensive look at the evolution of the equivalent schemes of ACTFEL devices from the early purely interfacial model to the most recent models enabling simulation of the space charge formation. Comparison of experimental and computer simulated characteristics of the ACTFEL stack may bring a better understanding of the possibilities of charge storage in various regions of the device and help in finding how this may impact device performance. Some peculiarities of the SPICE simulation of the devices are also discussed.

Main peculiarities of the characterization techniques are described and their role in the understanding of the device operation is presented. Some important features of the conventional characterization techniques, such as VIQ, PDP, L-V, Q-V, C-V, Q_max-V_max, and Q_p-F_int measurements in identifying carrier traps, their energy position, and some other main device parameters are emphasized. An important role of the destructive methods of analysis, such as the scanning election microscopy, secondary electron contrast profiling, and SIMS measurements of ACTFEL devices as complimentary tools to the non-destructive characterization techniques is demonstrated.

The paper addresses the well-known as well as “non-traditional” theoretical and experimental techniques of ACTFEL device analysis. The understanding of the ACTFEL devices can be greatly improved by using the innovative analogy approach of the analysis, some aspects of which were originally developed in Luxell and converted to a characterization technique.     

铁基氮化物在储能及电催化领域中的研究进展

氮化铁具有硬度高、熔点高、热导性高、耐腐蚀、安全无污染、电子导电性优异以及类铂的电子结构等优势,且其原材料资源丰富、成本低廉,在储能与电催化等众多领域中有着极大的应用前景。本文综述了铁基氮化物在结构、制备、性能和应用方面的研究进展,重点关注其制备方法和在储能领域(如锂离子电池、钠离子电池、锂硫电池)、电催化领域(如氢析出反应、氧析出反应、氧还原反应)中的应用,同时对铁基氮化物存在的主要问题进行了总结,对其未来的研究方向和应用前景进行了展望。     

基于ZnO电子传输层钙钛矿太阳能电池的研究进展

作为新一代低成本、高效率的光伏器件,以有机卤化铅CH₃NH₃PbX₃(MAPbX₃,X=Br、I、Cl)为光吸收层的钙钛矿太阳能电池(PSCs)相比于其他类型的光伏器件,具有原料丰富、工艺简单等特点。在较短的时间内,该类电池效率已由3.8%迅速攀升至25.7%,几乎可以媲美商用硅太阳能电池,成为能源应用领域的一颗新星。氧化锌(ZnO)因其具有材料易于加工、电子迁移率高、制造成本低廉且形貌结构多样等优点,被作为该类电池较为重要的一种电子传输层(ETL)而被广为研究。本文主要以不同结构的ZnO纳米薄膜ETL作为研究对象,对其在PSCs中的应用进行了总结,详细介绍了基于不同形貌ZnO纳米结构PSCs的研究进展,分析了该类电池面临的主要问题与解决处理方式,并对未来的发展趋势进行了展望。     

The Nature of One-sided Intergrowths on (001) of Triclinic Centrosymmetric K2Cr2O7

Systematic composite crystal growth can arise when larger crystals of the same type exhibit oriented intergrowth. One example of this is potassium dichromate (P1 ) which SHUBNIKOV first described in 1912. In highly supersaturated solutions, a one-sided roughening of its crystals occurs on (001 ). Electron micrographs show that this is due to the growth of platelet-shaped crystals. Optical and X-ray methods as well as electron channeling and BACK-KIKUCHI diffraction patterns have shown that the growths are predominantly parallel intergrowths, about 10% of which are twins according to [010].