Epitaxial growth of CsPbBr_(3)/PbS single-crystal film heterostructures for photodetection

Epitaxial high-crystallization film semiconductor heterostructures has been proved to be an effective method to prepare single-crystal films for different functional devices in modern microelectronics,electro-optics,and optoelectronics.With superior semiconducting properties,halide perovskite materials are rising as building blocks for heterostructures.Here,the conformal vapor phase epitaxy of CsPbBr3 on PbS single-crystal films is realized to form the CsPbBr3/PbS heterostructures via a two-step vapor deposition process.The structural characterization reveals that PbS substrates and the epilayer CsPbBr3 have clear relationships:CsPbBr3(110)//PbS(100),CsPbBr3[001]//PbS[001]and CsPbBr3[001]//PbS[010].The absorption and photoluminescence(PL)characteristics of CsPbBr3/PbS heterostructures show the broadband light absorption and efficient photogenerated carrier transfer.Photodetectors based on the heterostructures show superior photoresponsivity of 15 A/W,high detectivity of 2.65×10^(11) Jones,fast response speed of 96 ms and obvious rectification behavior.Our study offers a convenient method for establishing the high-quality CsPbBr3/PbS single-crystal film heterostructures and providing an effective way for their application in optoelectronic devices.

Relationship between the spatial position of the seed and growth mode for single-crystal diamond grown with an enclosed-type holder

The relationship between the spatial position of the diamond seed and growth mode is investigated with an enclosedtype holder for single-crystal diamond growth using the microwave plasma chemical vapor deposition epitaxial method.The results demonstrate that there are three main regions by varying the spatial position of the seed.Due to the plasma concentration occurring at the seed edge,a larger depth is beneficial to transfer the plasma to the holder surface and suppress the polycrystalline diamond rim around the seed edge.However,the plasma density at the edge decreases drastically when the depth is too large,resulting in the growth of a vicinal grain plane and the reduction of surface area.By adopting an appropriate spatial location,the size of single-crystal diamond can be increased from 7 mm×7 mm×0.35 mm to8.6 mm×8.6 mm×2.8 mm without the polycrystalline diamond rim.

Growth process,defects,and dopants of bulk β-Ga_(2)O_(3) semiconductor single crystals

β-gallium oxide(β-Ga2O3),as the typical representative of the fourth generation of semiconductors,has attracted increasing attention owing to its ultra-wide bandgap,superior optical properties,and excellent tolerance to high temperature and radiation.Compared to the single crystals of other semiconductors,high-quality and large-size β-Ga_(2)O_(3) single crystals can be grown with low-cost melting methods,making them highly competitive.In this review,the growth process,defects,and dopants ofβ-Ga_(2)O_(3) are primarily discussed.Firstly,the growth process(e.g.,decomposition,crucible corrosion,spiral growth,and development)ofβ-Ga_(2)O_(3) single crystals are summarized and compared in detail.Then,the defects of β-Ga_(2)O_(3) single crystals and the influence of defects on Schottky barrier diode(SBD)devices are emphatically discussed.Besides,the influences of impurities and intrinsic defects on the electronic and optical properties ofβ-Ga_(2)O_(3) are also briefly discussed.Concluding this comprehensive analysis,the article offers a concise summary of the current state,challenges and prospects ofβ-Ga_(2)O_(3) single crystals.

Evolution mechanism of crystallographic orientation in grain continuator bars of a Ni-based single-crystal superalloy prepared by Bridgman technology during directional solidification

Single-crystal rods with different diameters and deviation angles with respect to the solidification direction were produced by Bridgman rapid solidification method at withdrawal rates of 3 and 6 mm·min^(-1) and used as grain continuators.The crystallographic orientation of the rods,which cross-sections were perpendicular to the solidification direction at different solidification heights,was measured by electron backscattered diffraction,while the corresponding microstructures were observed by optical microscopy.The mushy zone morphology and the distribution of the temperature gradient were simulated by the finite element analysis software ProCAST.The experimental results indicate that the crystallographic orientation of the single-crystal rods corresponds to the statistical average value of all the dendrite orientations in cross-section.The crystallographic orientation of the primary and secondary dendrites of each single-crystal rod at different cross-sections fluctuates irregularly within a small range(less than 4°).The crystallographic orientation of the dendrite in each single-crystal rod is not exactly consistent with each other and is affected by their branching mode of dendrites in the solidification space.In addition,the simulation results show that the mushy zone shapes and the temperature gradient of single-crystal rods change with the increase of solidification height during the solidification process.Finally,the evolution mechanism of the crystallographic orientations and the corresponding influence factors were analyzed and discussed.

Numerical simulation of chemical vapor deposition reaction in polysilicon reduction furnace

Three-dimensional model of chemical vapor deposition reaction in polysilicon reduction furnace was established by considering mass, momentum and energy transfer simultaneously. Then, CFD software was used to simulate the flow, heat transfer and chemical reaction process in reduction furnace and to analyze the change law of deposition characteristic along with the H_2 mole fraction, silicon rod height and silicon rod diameter. The results show that with the increase of H_2 mole fraction, silicon growth rate increases firstly and then decreases. On the contrary, SiHCl_3 conversion rate and unit energy consumption decrease firstly and then increase. Silicon production rate increases constantly. The optimal H_2 mole fraction is 0.8-0.85. With the growth of silicon rod height, Si HCl3 conversion rate, silicon production rate and silicon growth rate increase, while unit energy consumption decreases. In terms of chemical reaction, the higher the silicon rod is, the better the performance is. In the view of the top-heavy situation, the actual silicon rod height is limited to be below 3 m. With the increase of silicon rod diameter, silicon growth rate decreases firstly and then increases. Besides, SiHCl_3 conversion rate and silicon production rate increase, while unit energy consumption first decreases sharply, then becomes steady. In practice, the bigger silicon rod diameter is more suitable. The optimal silicon rod diameter must be over 120 mm.

FAILURES AND THE LIFE OF FURNACE TUBES

It is showed after the furnace tubes serviced for 8-10 years that the density of damage in the HAZ (heat affected zone) of the weld has higher than in parent metals, though the depth of damage is not equal to. By the test of creep crack growth, it is also acquired that under same mechanic parameter C* (t), the rate of creep crack growth in the HAZ is more than twice as fast as in parent metals. Two mechanisms (overheating and thermal shock) of failure occurred in an accident are presented. The stress of thermal shock is analyzed, in which the change of the elasticity modulus with the radius ET = /(r) is considered. Based on it, the safety region of the thermal shock is obtained. Finally, two sets of curves for the safe life are suggested which can facilitate to estimate the remaining life of HK-40 or HP-Nb tubes by their creep rupture data.

Volume and Surface Nucleation of Crystals in Glass Based on Blast-Furnace Slag

Using differential thermal analysis, X-ray phase analysis, electron microscopy, and optical microscopy, the nucleation of crystals in glass obtained by blending metallurgical slag with silicon dioxide has been studied. The type of crystallization (homogeneous or heterogeneous, volume or surface) is revealed for each of nine compositions of synthesized glass. It is shown that the first crystalline phase in a volume crystallizing glass is perovskite (CaO·TiO2);in this phase a nucleation of the main phase occurs: melilite (solid solution of gehlenite 2CaO·Al2O3·SiO2 in akermanite 2CaO·MgO·2SiO2). The fundamental characteristics of homogeneous (for a catalizing phase, perovskite) and heterogeneous (for a catalyzed phase, melilite) of crystallization are determined: the steady state nucleation rate Ist, time of unsteady state nucleation τ, crystal growth rate U, and activation energy of frictional flow. The temperature dependences of Ist, τ, and U are obtained. The kinetics of the crystallization of glass is studied and the rates of the surface crystal growth are determined in the glass of nine compositions. The influence of grinding the particles of the original glass on the sequence of deposition of the crystalline phases was studied. Practical recommendations are presented for the use of blast-furnace slag as a raw material for the synthesis of glass and their further utilization.

基于8英寸的碳化硅单晶生长炉技术

碳化硅是制作高温、高频、大功率以及高压器件的理想材料之一。为提高生产效率并降低成本,大尺寸碳化硅衬底的制备是重要发展方向。针对8英寸碳化硅单晶生长的工艺需求,分析了碳化硅物理气相输运法生长机理,研究了碳化硅单晶生长炉的加热系统、坩埚旋转、工艺参数控制技术,通过热场模拟仿真分析和工艺试验,成功制备生长了8英寸晶体。

红外测温仪在碳化硅单晶生长炉中的应用

碳化硅单晶生长炉的温度监测及控制是碳化硅晶体生长工艺的关键。针对碳化硅单晶生长炉的高温测量需求及使用工况,分析了红外测温仪测温的工作原理及分类,研究了碳化硅单晶生长炉的测温结构及温度控制技术。通过引入模糊PID算法实现了热场温度的稳定控制,经过升温测试试验,达到碳化硅工艺生长的要求。

Influence of relative positions between RF coil and crucible on sapphire crystals by edge-defined film-fed growth(EFG) technique

To obtain the stable temperature field required for growing sapphire crystals, the influence of relative positions between RF coil and crucible on the performances of sapphires produced by edge-defined film-fed growth（EFG） technique was investigated. For comparison, the crucible was located at the top（case A） and the middle（case B） of the RF coil, respectively. Furthermore, the lattice integrities were studied by the double-crystal X-ray diffraction, and the dislocations were observed under the optical microscope and atomic force microscope after corroding in molten KOH at 390 ℃. The crystals in case B exhibit better lattice integrity with smaller full width at half maximum of 29.13 rad·s, while the value in case A is 45.17 rad·s. The morphologies of dislocation etch pits in both cases show typical triangular symmetry with smooth surfaces. However, the dislocation density of 2.8×104 cm-2 in case B is only half of that in case A, and the distribution is more uniform, compared to the U-shaper in case A.

常压/低压一体化CVD生长系统的设计与应用

为了实现半导体纳米材料的高效安全制备,结合不同材料的生长要求,设计并搭建了一套常压/低压一体化CVD生长系统。该生长系统主要由管式生长炉、配气单元和尾气回收处理单元三部分构成。系统配置单温区、双温区和三温区管式炉,采用机械泵/分子泵与高精度真空计准确调控管内压强,可实现不同压强条件下多种半导体纳米材料的高效制备;安装了可燃气体自动探测、报警、断气一体化装置,增加了阻火防燃、泄气防爆等装置,可有效提高系统的安全性。该生长系统具有操作简单、功能多样、安全可靠等优点,应用此系统已成功生长出二十余种高质量的新型半导体纳米材料,取得了一系列重要学术成果。

碲锌镉晶体VGF法生长温场的梯度区高度设计研究

本文对不同梯度区高度的VGF法温场生长碲锌镉(CdZnTe)晶体过程进行了稳态和非稳态仿真模拟分析。研究发现,晶体生长等径初期界面凸度随着梯度区高度的增加而减小;等径末期界面凸度受梯度区高度的影响不大;界面的凸度与固液界面温度梯度变化率正相关。非稳态模拟结果显示,现有变温条件下,晶体生长过程中固液界面凸度存在先增大后减小的趋势,趋势转变点接近梯度区高度中点;界面形状的变化趋势受固液界面上生长速度分布直接影响;对比而言,10 cm高的梯度区更容易实现前中期固液界面凸界面的获得,利于形成高单晶率CdZnTe晶体。

Effect of substrate preset temperature on crystal growth and microstructure formation in laser powder deposition of single-crystal superalloy

A successful repair of single-crystal components needs to avoid the stray grain formation and achieves continuous epitaxial growth of columnar dendrites in the repaired zone. In this study, the effect of substrate preset temperature on crystal growth and microstructure formation in laser powder deposition of single-crystal superalloy was studied through an improved mathematical model and corresponding experimental approaches. The results indicated that the variation of substrate preset temperature between-30℃ and ＋210℃ changes the molten pool morphology little, but obviously affects the columnar-to-equiaxed transition conditions. The preheating of substrate facilitates the stray grain formation and enlarges the primary columnar dendrite arm spacing, while the situation for precooling of substrate is opposite. Under the specific processing conditions, the critical condition for continuous epitaxial growth is that the substrate preset temperature Tsub≤ ＋90℃. When the substrate preset temperature Tsubis below ＋90℃, the height ratio of melting depth to total height of the molten pool is larger than that of stray grain, ensuring that stray grains can be completely remelted and the continuous columnar dendrites during the multi-layer laser powder deposition process on（001） surface of single-crystal substrate can be achieved.

旋转编码开关在PLC项目中的应用

针对PLC项目中的某些参数调节问题,研究了带按键旋转编码开关的工作原理及使用方法。基于西门子S7-1200系列PLC设计了实验,包括硬件配置、接线图及程序设计。通过研究带按键旋转编码开关的工作原理,并对其输出信号进行了分析。根据元件输出特性对PLC进行编程,完成了对开关旋转方向的判别及信号提取。经实验验证,该设计能够实现对参数增减的灵活调节功能,带按键旋转编码开关具有可靠性高、操作便捷、控制精准、调节范围广等特点,将其应用到基于PLC的晶体生长炉控制系统中,使得对晶体生长控制系统的操作更加便捷。

Solid-state single-crystal growth of YAG and Nd: YAG by spark plasma sintering

Recent studies have shown that many challenges encountered in conventional single crystal growth methods, including high production costs, can be overcome by using the solid-state single-crystal growth(SSCG) approach, which has been recognized as a simple and cost-effective alternative for obtaining single crystals. In this work, YAlO(YAG) and Nd-doped YAG(Nd:YAG) single crystals were grown via the SSCG method using spark plasma sintering(SPS). The growth of single crystals was initiated at the surface of(110) YAG single-crystal seeds embedded inside YAG and Nd:YAG powder beds, and this growth continued as the surrounding polycrystalline matrix was converted into a single crystal. The application of external pressure during the SPS process has been found beneficial for reducing the porosity of the grown single crystals. Moreover, high Nddoping levels had a positive effect on the conversion kinetics,with a growth rate of almost 50 μm/h, which increased the driving force for single-crystal growth through the solute drag effect. EDS elemental mapping and line scans confirmed the compositional uniformity of the grown single crystals, while EBSD images verified their crystallization in the(110) direction. The obtained results confirm the strong potential of the SSCG technique coupled with SPS for the growth of undoped and highly doped YAG single crystals with excellent quality.

含钛高炉渣中CaO和MnO对钙钛矿结晶的影响

含钛高炉渣中钛组分弥散分布于多种矿物相中 ,很难直接用选矿方法分离。在高炉渣中加入 Ca O和 Mn O可使钛富集于充分结晶长大的钙钛矿相中 ,为选矿分离创造必要条件。作者借助多视场图像分析及粘度测定研究了 Ca O、Mn O对钙钛矿相结晶的影响。实验结果表明 :Ca O加入量对钙钛矿结晶及晶体生长有双重影响。加入适量 Ca O,有利于钙钛矿相结晶量的增加 ,但 Ca O加入量过多 ,使熔渣粘度及熔化性温度显著提高 ,反而抑制钙钛矿结晶长大。加入适量 Mn O可显著降低熔渣粘度及熔化性温度 ,促进钙钛矿结晶长大。随 Ca O加入量提高 ,钙钛矿由粗大的树枝晶转变为细小等轴晶 ,说明加入过多 Ca O不利于钙钛矿晶体粗化。

晶体生长炉的PID神经网络温度控制算法

本文采用了数字PID与神经网络相融合的晶体生长炉温度测控方法,设计了生长晶体的PID神经网络温度控制器,并用FPGA(Field Programmable Gate Array)实现了PID神经网络的并行结构;神经网络采用符合32位IEEE754的单精度浮点数运算单元。理论分析和仿真结果表明:该PID神经网络温度控制器具有很高的控制精度和响应速度,有利于提高晶体生长炉的控温精度和加热效率。

“化学炉”加机械压力法超快速制备超细晶氧化铝陶瓷

报道了一种制备具有微米级以下微观结构的完全致密氧化铝(Al2O3)陶瓷的新方法。用燃烧合成所产生的热量为热源代替传统烧结炉。用燃烧合成原料将Al2O3包裹起来作为“化学炉”,在燃烧反应完成的同时施加机械压力快速烧结制备Al2O3陶瓷。实验中,用平均粒径为600nm的Al2O3为原料,当施加的压力为120MPa时,得到完全致密的烧结体,整个过程为5min。扫描电镜和透射电镜分析结果显示:烧结后晶粒间结合良好,平均尺寸为600nm,与原料粒径相比无明显长大。

基于双摆模型的单晶炉提拉系统摆动现象动力学分析

针对单晶炉旋转提拉系统在运行中出现的摆动现象进行了建模和数值仿真。将该旋转提拉系统简化为在支座简谐激励下的双摆力学模型,模型中考虑了提拉软轴及提拉头的质量,以及系统的阻尼。应用拉格朗日方程导出了该系统的非线性振动方程并加以线性化,通过模态分析将耦合的双自由度振动方程化为两个单自由度方程。应用Matlab平台进行数值仿真,模拟出了提拉系统振动幅值随旋转频率的变化关系。理论分析结果与实际中观察到的现象一致。研究结果为改善提拉系统的动态性能,减小提拉系统的摆动幅值提供了理论方法和依据。

全自动提拉单晶炉系统控制技术

详细阐述了一种全新单晶炉自动控制系统,该系统采用工业控制计算机为数据控制核心,上称重控制传感器进行晶体数据采集,利用感应加热或电阻加热方式控制单晶炉温场。通过对单晶炉控制系统特性研究和热场模型的正确推导,有效解决了系统温场及晶体结晶过程中引发的大滞后及系统非线性控制问题。试验结果表明,该系统控制稳定可靠,各项性能指标均达到国际先进水平。