Pulsed metal organic chemical vapor deposition of InAlN-based heterostructures and its application in electronic devices

As a promising group III-nitride semiconductor material, InAlN ternary alloy has been attracted increasing interest and widespread research efforts for optoelectronic and electronic applications in the last 5 years. Following a literature survey of current status and progress of InAlN- related studies, this paper provides a brief review of some recent developments in InAlN-related III-nitride research in Xidian University, which focuses on innovation of the material growth approach and device structure for electronic applications. A novel pulsed metal organic chemical vapor deposition （PMOCVD） was first adopted to epitaxy of InAlN-related heterostructures, and excellent crystalline and electrical properties were obtained. Furthermore, the first domestic InAlN-based high-electron mobility transistor （HEMT） was fabricated. Relying on the PMOCVD in combination with special GaN channel growth approach, high-quality InAlN/GaN double-channel HEMTs were successfully achieved for the first time. Additionally, other potentiality regarding to AlGaN channel was demonstrated through the successful realization of nearly lattice-matched InAlN/AlGaN heterostructures suitable for high-voltage switching applications. Finally, some advanced device structures and technologies including excellent work from several research groups around the world are summarized based on recent publications, showing the promising prospect of InAlN alloy to push group III-nitride electronic device performance even further.     

Research progress in ZnO single-crystal: growth,scientific understanding,and device applications

Zinc oxide, a wide band-gap semiconductor, has shown extensive potential applications in high-efficiency semiconductor photoelectronic devices, semiconductor photocatalysis, and diluted magnetic semiconductors. Due to the undisputed lattice integrity, ZnO single crystals are essential for the fabrication of high-quality ZnO-based photoelectronic devices, and also believed to be ideal research subjects for understanding the underlying mechanisms of semiconductor photocatalysis and diluted magnetic semiconductors. This review, which is organized in two main parts, introduces the recent progress in growth, basic characterization, and device development of ZnO single crystals, and some related works in our group. The first part begins from the growth of ZnO single crystal, and summarizes the fundamental and applied investigations based on ZnO single crystals. These works are composed of the fabrication of homoepitaxial ZnO-based photoelectronic devices, the research on the photocatalysis mechanism, and dilute magnetic mechanism. The second part describes the fabrication of highly thermostable n-type ZnO with high mobility and high electron concentration through intentional doping. More importantly, in this part, a conceptual approach for fabricating highly thermostable p-type ZnO materials with high mobility through an integrated three-step treatment is proposed on the basis of the preliminary research.     

III族氮化物半导体异质结构中载流子的量子输运和自旋性质

III族氮化物半导体具有宽的直接带隙,很强的极化电场,优异的物理特性,是发展高频、高温、高功率电子器件和光电子器件的优选材料．同时,III族氮化物半导体有很长的电子自旋弛豫时间以及很高的居里温度,也成为近年来半导体自旋电子学研究的重要材料体系之一．本文介绍了用量子输运和自旋光电流方法对Gain基异质结构中载流子的量子输运和自旋性质的研究进展．对III族氮化物半导体中的能带结构,子带占据和散射,自旋分裂及自旋轨道耦合机制等进行了讨论．     

粘附和根切对模态局部化加速度计的影响

为研究基于单面刻蚀的微机电系统制造工艺对模态局部化加速度计的影响,通过分析释放和刻蚀工艺对模态局部化加速度计结构的影响以及对加速度计幅频特性和初始工作点的影响研究了粘附和根切对模态局部化加速度计的影响。结果表明：释放氧化层时由于液体张力的存在极易使得器件层与基底层发生粘附,导致器件失效;根切会导致谐振器之间的质量差异,从而导致加速度计初始幅值比较大的漂移,增加了信号检测的难度。可见基于单面刻蚀的微机电系统制造工艺会增加模态局部化加速度计传感器的不确定性。     

GaAs/AlGaAs多量子阱红外探测材料的结构厚度获取方法

通过常规的透射光谱测量,提供一种获取GaAs/AlGaAs多量子阱材料中上电极层、多量子阱区域实际生长厚度的简便、无损伤的方法,这两个厚度参数在器件制备工艺、材料生长参数修正中起关键作用.     

面向HgCdTe红外焦平面探测器应用的分子束外延材料研究进展

报道了针对第三代碲镉汞红外焦平面的应用需求进行的碲镉汞分子束外延研究进展.面向大规模HgCdTe红外焦平面探测器的应用,开展了大面积替代衬底上的分子束外延技术研究,报道了在大面积替代衬底上的碲镉汞分子束外延材料的晶体质量、表面形貌和组份均匀性的改善方法和研究结果.512×512及以上规模的中波、短波碲镉汞面阵器件制备验证表明Si基碲镉汞材料满足应用需求.围绕甚长波红外焦平面探测器及雪崩红外焦平面探测器的研制需要,开展了低缺陷的ZnCdTe基碲镉汞分子束外延研究.外延获得的HgCdTe外延材料均匀性得到明显提高.经过外延条件的优化,厚度为10μm的HgCdTe/ZnCdTe(组分x=0.22)分子束外延材料位错密度最好结果为3×104 cm-2,双晶半峰宽小于25弧秒.     

应用于空基相控阵雷达的新型功率器件一-SIC 射频功率MESFET

根据空基相控阵雷达的工作环境，对4H—SiC材料及SiC功率器件(SiC MESFET)的特点进行了分析。与GaAs器件相比，这种新型器件在空基相控阵雷达领域有广泛的应用前景。同时建立了用于器件CAD技术的SiC MESFET改进型非线性大信号模型，这种基于实验测量的模型通过SPICE模拟器对器件的功率特性进行了分析，与实验结果符合较好。     

基底材料对MoS2的应变场影响

利用有限元法分析对生长在Au、Cu、Al₂O₃、SiO₂、Ni这5种不同基底上的层状MoS₂的应变分布进行模拟仿真.研究结果表明:基底材料的泊松比不同会使得基底和MoS₂的y方向形变都不相同; 基底的杨氏模量不同会使得不同基底底部与二硫化钼(MoS₂)顶部的应变差别不同.在膨胀过程中,y方向底端的拉伸应变大于中间的拉伸应变,这会导致基底与顶端应变高于中间的应变.因此,基底材料的杨氏模量和泊松比与MoS₂的应变分布密切相关.根据仿真结果可得,由于MoS₂在Au和SiO₂基底上所受到的应变较小,导致MoS₂的顶端和基底底部应变差较大,因此容易造成剥离脱落; 而在Al₂O₃基底上,由于基底材料具有较高的杨氏模量,且与MoS₂比较接近,所以MoS₂顶端和基底底部呈现的应变差接近.由此可见,在这些材料当中,Al₂O₃更适合作为MoS₂的基底材料.通过研究基底材料的应变场分布,能更好地对纳米材料进行调控,从而改善器件的相关性能.     

聚合物分散液晶器件的制备与电光性能

为探索智能变色伪装材料技术途径,采用光引发聚合物相分离的方法制备了聚合物分散液晶(PDLC)器件,研究了聚合物含量对PDLC器件微观形貌和电光性能的影响,考察了液晶盒厚对PDLC器件电光性能的影响.结果表明,当聚合物含量为40％,液晶盒厚为9.8 μm时,PDLC器件工作电压低、对比度高、性能稳定,对制备柔性变色智能伪...     

脉冲激光沉积技术

薄膜技术作为一种有效的手段为材料的集成和器件的制备提供了坚实的基础.本文主要介绍脉冲激光沉积技术的基本原理、特点、优点和缺点.该方法尤其适合用来生长多组分、化学结构复杂的过渡金属氧化物薄膜.     

Layered boron nitride as a release layer for mechanical transfer of GaN-based devices

Nitride semiconductors are the materials of choice for a variety of device applications, notably optoelectronics and high-frequency/high-power electronics. One important practical goal is to realize such devices on large, flexible and affordable substrates, on which direct growth of nitride semiconductors of sufficient quality is problematic. Several techniques--such as laser lift-off--have been investigated to enable the transfer of nitride devices from one substrate to another, but existing methods still have some important disadvantages. Here we demonstrate that hexagonal boron nitride (h-BN) can form a release layer that enables the mechanical transfer of gallium nitride (GaN)-based device structures onto foreign substrates. The h-BN layer serves two purposes: it acts as a buffer layer for the growth of high-quality GaN-based semiconductors, and provides a shear plane that makes it straightforward to release the resulting devices. We illustrate the potential versatility of this approach by using h-BN-buffered sapphire substrates to grow an AlGaN/GaN heterostructure with electron mobility of 1,100?cm(2)?V(-1)?s(-1), an InGaN/GaN multiple-quantum-well structure, and a multiple-quantum-well light-emitting diode. These device structures, ranging in area from five millimetres square to two centimetres square, are then mechanically released from the sapphire substrates and successfully transferred onto other substrates.     

Growth dynamics of pentacene thin films

The recent demonstration of single-crystal organic optoelectronic devices has received widespread attention. But practical applications of such devices require the use of inexpensive organic films deposited on a wide variety of substrates. Unfortunately, the physical properties of these organic thin films do not compare favourably to those of single-crystal materials. Moreover, the basic physical principles governing organic thin-film growth and crystallization are not well understood. Here we report an in situ study of the evolution of pentacene thin films, utilizing the real-time imaging capabilities of photoelectron emission microscopy. By a combination of careful substrate preparation and surface energy control, we succeed in growing thin films with single-crystal grain sizes approaching 0.1 millimetre (a factor of 20-100 larger than previously achieved), which are large enough to fully contain a complete device. We find that organic thin-film growth closely mimics epitaxial growth of inorganic materials, and we expect that strategies and concepts developed for these inorganic systems will provide guidance for the further development and optimization of molecular thin-film devices.     

仿生材料设计与制备的研究进展

自然界中一些生物体的优异结构和特性给人类在不断制造和更新新型材料的过程中带来灵感和启发．根据这些生物体的优秀特征综述仿生材料的主要设计思想和方法，重点分析目前一些典型仿生材料如仿生复合材料、仿生陶瓷材料、仿生纳米材料和仿生涂层材料等设计和制备研究的新进展和存在的困难，并提出一些新的材料设计思想方法和制备的模型，对仿生材料的设计和研究等均具有指导意义，最后则展望了仿生材料的发展前景．     

激光熔覆层网状添加物对裂纹控制的影响

激光熔覆是新型表面强化技术,但熔覆层裂纹是限制其应用的主要难题．在熔覆层中加入不锈钢网,降低了熔覆层中的应力值,控制了熔覆层中的裂纹．对3种熔覆材料的实验验证了网丝的加入能有效地降低熔覆层的裂纹率．金相分析显示,随着网丝直径的增大,熔覆层中网丝未完全熔解,它与熔覆材料、基体形成冶金结合,保证了熔覆层的完整性,有效地控制了熔覆层的裂纹．实验工艺显示,对Ni45和Co02这2种粉末,在基体不预热的情况下,这项工艺技术可得到无裂纹的大面积熔覆层．     

Patterning organic single-crystal transistor arrays

Field-effect transistors made of organic single crystals are ideal for studying the charge transport characteristics of organic semiconductor materials. Their outstanding device performance, relative to that of transistors made of organic thin films, makes them also attractive candidates for electronic applications such as active matrix displays and sensor arrays. These applications require minimal cross-talk between neighbouring devices. In the case of thin film systems, simple patterning of the active semiconductor layer minimizes cross-talk. But when using organic single crystals, the only approach currently available for creating arrays of separate devices is manual selection and placing of individual crystals-a process prohibitive for producing devices at high density and with reasonable throughput. In contrast, inorganic crystals have been grown in extended arrays, and efficient and large-area fabrication of silicon crystalline islands with high mobilities for electronic applications has been reported. Here we describe a method for effectively fabricating large arrays of single crystals of a wide range of organic semiconductor materials directly onto transistor source-drain electrodes. We find that film domains of octadecyltriethoxysilane microcontact-printed onto either clean Si/SiO(2) surfaces or flexible plastic provide control over the nucleation of vapour-grown organic single crystals. This allows us to fabricate large arrays of high-performance organic single-crystal field-effect transistors with mobilities as high as 2.4 cm(2) V(-1) s(-1) and on/off ratios greater than 10(7), and devices on flexible substrates that retain their performance after significant bending. These results suggest that our fabrication approach constitutes a promising step that might ultimately allow us to utilize high-performance organic single-crystal field-effect transistors for large-area electronics applications.     

A graphene-based broadband optical modulator

Integrated optical modulators with high modulation speed, small footprint and large optical bandwidth are poised to be the enabling devices for on-chip optical interconnects. Semiconductor modulators have therefore been heavily researched over the past few years. However, the device footprint of silicon-based modulators is of the order of millimetres, owing to its weak electro-optical properties. Germanium and compound semiconductors, on the other hand, face the major challenge of integration with existing silicon electronics and photonics platforms. Integrating silicon modulators with high-quality-factor optical resonators increases the modulation strength, but these devices suffer from intrinsic narrow bandwidth and require sophisticated optical design; they also have stringent fabrication requirements and limited temperature tolerances. Finding a complementary metal-oxide-semiconductor (CMOS)-compatible material with adequate modulation speed and strength has therefore become a task of not only scientific interest, but also industrial importance. Here we experimentally demonstrate a broadband, high-speed, waveguide-integrated electroabsorption modulator based on monolayer graphene. By electrically tuning the Fermi level of the graphene sheet, we demonstrate modulation of the guided light at frequencies over 1?GHz, together with a broad operation spectrum that ranges from 1.35 to 1.6?μm under ambient conditions. The high modulation efficiency of graphene results in an active device area of merely 25?μm(2), which is among the smallest to date. This graphene-based optical modulation mechanism, with combined advantages of compact footprint, low operation voltage and ultrafast modulation speed across a broad range of wavelengths, can enable novel architectures for on-chip optical communications.     

Large scale production of carbon nanotube arrays on the sphere surface from liquefied petroleum gas at low cost

Liquefied petroleum gas (LPG), a cheap industrial material, is used as carbon source to produce carbon nanotube (CNT) arrays on ceramic spherical surface on a large scale in the floating catalyst process. The ceramic spheres provide huge surface area and good mobility, leading to the mass production of CNT arrays continuously. The arrays obtained from the surface are of good alignment, and the purity is as high as 97.5%. With the decrease of the growth temperature, CNTs in the array form with small-diameter of about 13 nm can be obtained. Therefore, with the industrial fuel as carbon source and the ceramic sphere as substrate, CNT arrays can easily be produced on large scale at low cost.     

高温超导材料特性数据处理系统的设计与实现

介绍了BW2型高温超导材料特性测试装置计算机数据采集和处理系统的设计与实现过程，在仪器手动测试功能的基础上，增加了数据自动采集、存储、处理等功能，不仅完善了该实验装置，而且提高了测试精度，通过该系统，学生不仅能动手操作了解高温超导材料特性测试的全过程，而且能够再现实验过程，有利于高温超导电性的进一步研究。     

聚甲基红膜修饰电极的制备及其对抗坏血酸的电催化性能研究

研究了聚甲基红膜修饰电极(PMRE)的制备方法及其在水溶液中的电化学行为,用循环伏安技术对该膜的电化学特性进行了初步的探讨,结果表明PMRE对抗坏血酸具有很好的电催化作用．催化峰电流与底物浓度在较宽的范围内有良好的线性关系,可用于实际样品分析。     

S-scheme ZnO/MoS2异质结构筑与对盐酸四环素降解性能

抗生素药物使用范围广且用量大,导致大量抗生素废水进入水体或者残留在土壤环境中,对人类健康造成威胁,然而传统工艺对其去除效果并不理想.以ZnO为基底,通过掺杂MoS₂,制备了S-scheme ZnO/MoS₂异质结复合材料,研究了该材料对抗生素废水的净化性能.通过调节复合材料中ZnO含量、光照条件、盐酸四环素浓度等,探讨了ZnO/MoS₂复合材料对不同浓度盐酸四环素(tetracycline hydrochloride,TC)废水的净化效果.结果表明:在光照条件下,催化剂复合比为1∶1的ZnO/MoS₂复合材料对60 mg·L^－1四环素废水的降解效率可达88%(pH=7,105 min);电子传递与污染物降解机理研究表明,电子由ZnO导带迁移至MoS₂价带,形成S-scheme异质结,从而有效提高了催化效率与污染物降解性能.