可调谐氮化硅波导微环谐振腔滤波器研究

设计并制备了一种基于热光效应的集成可调谐氮化 硅(Si₃N₄)波导微环谐振腔滤波器,通过采用马赫-曾德干涉仪(MZI)构成的可调谐 耦合器控制耦合区耦合比,以实现滤波器消光比的调谐。设计并优化了微环谐振 腔的波导截面尺寸、弯曲半径和耦合区波导间隔等参数,并通过光刻、反应离子刻蚀(RIE )等工艺制备 了两种不同弯曲半径的Si₃N₄波导微环谐振腔。实验结果表明,本文器件在波长1550nm附近处的自由光谱 范围(FSR)为68pm,3dB带宽约为16pm,品质因子Q达到了9.68×10 4,消光比可调范围约为17dB。     

基于Si3N4掩模的太阳电池选择性掺杂工艺研究

设计了基于Si3N4掩模的太阳电池选择性掺杂工艺,并对其工艺参数进行了仿真优化。选择性掺杂电池的一次掺杂条件为仿真所得最佳非选择性掺杂电池的工艺参数。运用SILVACO软件分别对选择性掺杂的时间、预淀积浓度和温度进行了仿真研究。仿真结果表明,随着选择性掺杂的预淀积浓度的增加,光谱响应率先增加后降低;随着扩散温度和扩散时间的增加,电池的光谱响应率逐渐减小。所得最佳选择性掺杂工艺参数为预淀积磷硅玻璃杂质浓度1×1019 cm-3、扩散温度800℃、扩散时间5min。     

Mechanism of selective Si3N4 etching over SiO2 in hydrogen-containing fluorocarbon plasma

This paper describes the mechanism of selective Si₃N₄ etching over SiO₂ in capacitively-coupled plasmas of hydrogen-containing fluorocarbon gas, including CHF₃, CH₂F₂ and CH₃F. The etch rate of Si₃N₄ and SiO₂ is investigated as a function of O₂ percentage in all plasma gases. Addition of O₂ in feed gases causes plasma gas phase change especially H density. The SiO₂ etch rate decreases with increase of O₂ percentage due to the decline of CF_x etchant. The Si₃N₄ etch rate is found to be strong correlated to the H density in plasma gas phase. H can react with CN by forming HCN to reduce polymer thickness on Si₃N₄ surface and promote the removal of N atoms from the substrate. Thus the Si₃N₄ etch rate increases with H intensity. As a result, a relative high selectivity of Si₃N₄ over SiO₂ can be achieved with addition of suitable amount of O₂ which corresponds to the maximum of H density.     

基于氮化硅陶瓷毛细芯的低温回路热管研究

利用氮化硅陶瓷多孔材料作为毛细芯设计了一种以乙烷为工质的低温回路热管样机, 并对其降温及传热性能进行了研究。试验结果表明,通过在蒸发器上施加4 W的热量, 这种低温回路热管能够在常温下实现启动,并能顺利实现降温;在降温过程中,通过不断增大加热功率,可以加快低温回路 热管的降温;当蒸发器的温度为190 K时,该样机可以稳定传输30 W的热量。     

用于非易失性相变存储器中Si2Sb2Te5在CF4/Ar等离子体下的反应离子刻蚀

Phase change random access memory（PCRAM） is one of the best candidates for next generation nonvolatile memory,and phase change Si₂Sb₂Te₅ material is expected to be a promising material for PCRAM.In the fabrication of phase change random access memories,the etching process is a critical step.In this paper,the etching characteristics of Si₂Sb₂Te₅ films were studied with a CF₄/Ar gas mixture using a reactive ion etching system.We observed a monotonic decrease in etch rate with decreasing CF4 concentration,meanwhile,Ar concentration went up and smoother etched surfaces were obtained.It proves that CF4 determines the etch rate while Ar plays an important role in defining the smoothness of the etched surface and sidewall edge acuity.Compared with Ge₂Sb₂Te₅, it is found that Si₂Sb₂Te₅ has a greater etch rate.Etching characteristics of Si₂Sb₂Te₅ as a function of power and pressure were also studied.The smoothest surfaces and most vertical sidewalls were achieved using a CF₄/Ar gas mixture ratio of 10/40,a background pressure of 40 mTorr,and power of 200 W.     

Comparative measurements of the electron emission behavior of Si3N4-InGaAs interfaces prepared by remote and direct PECVD

The effects on the insulator-semiconductor interface of two different deposition methods of silicon nitride on In_0.53Ga_0.47As have been electronically studied using capacitance-voltage (CV) and deep level transient spectroscopy (DLTS) measurements. The CV data showed very similar behavior on both types of sample, but the DLTS results were surprisingly different. The behavior of samples fabricated using direct plasma enhanced chemical vapor deposition (PECVD) can be explained by electronic emission from interface states to the conduction band minimum. However, the remote PECVD method gave a DLTS peak corresponding to electron emission with a low activation energy ≈0.13 eV. As with the direct PECVD samples, the thermal activation energy decreased as the bias was made more positive, but in this case the change in emission energy was only a fraction of the shift in the Fermi level position. A model is proposed involving the concepts of lattice relaxation and hole capture to explain this behavior.     

Co3O4/Fe2O3异质结复合材料的制备及其紫外光光电探测性能

分别采用旋涂法和水热法在FTO衬底上制备Co₃O₄种子层和Co₃O₄薄膜,再在Co₃O₄薄膜上水热生长Fe₂O₃纳米棒,获得了高质量的Co₃O₄/Fe₂O₃异质结复合材料。通过改变Fe₂O₃前驱体溶液浓度来改变异质结复合材料中Fe₂O₃组分的含量。结果表明,Fe₂O₃纳米棒覆盖在呈网状结构的Co₃O₄薄膜上,随着Fe₂O₃前驱体溶液浓度即Fe₂O₃组分含量的增加,Co₃O₄/Fe₂O₃异质结复合材料对紫外光的响应逐渐增强,当Fe₂O₃前驱体溶液浓度为0.015mol/L时,异质结复合材料有着很好的光电稳定性,并表现出较高的响应率(12.5mA/W)和探测率(4.4×10¹⁰Jones)。     

Fabrication of high-Ge-fraction strained Si1−xGex/Si hole resonant tunneling diode using low-temperature Si2H6 reaction for nanometer-order ultrathin Si barriers

Low-temperature Si barrier growth with atomically flat heterointerfaces was investigated in order to improve negative differential conductance (NDC) characteristics of high-Ge-fraction strained Si_1−xGe_x/Si hole resonant tunneling diode with nanometer-order thick strained Si_1−xGe_x and unstrained Si layers. Especially to suppress the roughness generation at heterointerfaces for higher Ge fraction, Si barriers were deposited using Si₂H₆ reaction at a lower temperature of 400 °C instead of SiH₄ reaction at 500 °C after the Si_0.42Ge_0.58 growth. NDC characteristics show that difference between peak and valley currents is effectively enhanced at 11-295 K by using Si₂H₆ at 400 °C, compared with that using SiH₄ at 500 °C. Non-thermal leakage current at lower temperatures below 100 K tends to increase with decrease of Si barrier thickness. Additionally, thermionic-emission dominant characteristics at higher temperatures above 100 K suggests a possibility that introduction of larger barrier height (i.e. larger band discontinuity) enhances the NDC at room temperature by suppression of thermionic-emission current.     

Effects of CH2F2 and H2 flow rates on process window for infinite etch selectivity of silicon nitride to ArF PR in dual-frequency CH2F2/H2/Ar capacitively coupled plasmas

The process window for the infinite etch selectivity of silicon nitride (Si₃N₄) layers to ArF photoresist (PR) and ArF PR deformation were investigated in a CH₂F₂/H₂/Ar dual-frequency superimposed capacitive coupled plasma (DFS-CCP) by varying the process parameters, such as the low frequency power (P_LF), CH₂F₂ flow rate, and H₂ flow rate. It was found that infinitely high etch selectivities of the Si₃N₄ layers to the the ArF PR on both the blanket and patterned wafers could be obtained for certain gas flow conditions. The H₂ and CH₂F₂ flow rates were found to play a critical role in determining the process window for infinite Si₃N₄/ArF PR etch selectivity, due to the change in the degree of polymerization. The preferential chemical reaction of hydrogen with the carbon in the hydrofluorocarbon (CH_xF_y) layer and the nitrogen on the Si₃N₄ surface, leading to the formation of HCN etch by-products, results in a thinner steady-state hydrofluorocarbon layer and, in turn, in continuous Si₃N₄ etching, due to enhanced SiF₄ formation, while the hydrofluorocarbon layer is deposited on the ArF photoresist surface.     

WO3/NiWO4复合薄膜的制备及其光电化学性能

采用两步水热法在导电玻璃(FTO)上制备了WO₃/NiWO₄复合薄膜。通过XRD,SEM表征了WO₃/NiWO₄复合薄膜的组成结构及微观形貌,利用UV-Vis、光电流测试、光电催化测试和交流阻抗测试分析了WO₃/NiWO₄复合薄膜的光电性能。结果表明:WO₃/NiWO₄复合薄膜相较于WO₃薄膜具有更好的光吸收特性、光电流密度和光电催化活性,其中水热反应3h的WO₃/NiWO₄复合薄膜的光电化学性能最佳。WO₃/NiWO₄-3h在1.4V(vs.Ag/AgCl)时的光电流密度为1.94mA/cm²,光电催化210min对亚甲基蓝溶液的降解效率为57.1%。交流阻抗图谱表明WO₃/NiWO₄薄膜的电荷转移电阻小于WO₃薄膜,光电化学性能更优。     

Low temperature sintering properties of Y-doped BaTiO3 ceramics by BaB2O4 sintering aid

The sintering process of semiconducting Y-doped BaTiO₃ ceramics added with BaB₂O₄ as low temperature sintering aid were investigated. When the low temperature sintering aid BaB₂O₄ added Y-doped BaTiO₃ ceramics prepared by Sol-Gel method, the sintering temperature of BaTiO₃-based ceramics would be greatly decreased, and also widen sintering range. Y-doped BaTiO₃ ceramics with BaB₂O₄ addition can be obtained at 1050 °C. Ceramics samples with room temperature resistivity 60-80 Ω cm, ratio of the maximum resistivity to minimum resistance (Rmax/Rmin) 10⁴ and temperature coefficient of resistivity (α) 10%/°C were obtained.     

Growth and characterization of Tl3InSe4 single crystals

Tl₃InSe₄ single crystal has been successfully prepared by the Bridgman crystal growth technique. The crystal that is reported for the first time is found to be of tetragonal structure with lattice parameters of a=0.8035 and c=0.6883 nm. The electrical resistivity and Hall effect measurements on the crystal revealed a conductivity type conversion from p- to n-type at a critical temperature of 283 K. The electron to hole mobility ratio is found to be 1.10. The analysis of the temperature-dependent electrical resistivity, Hall coefficient and carrier concentration data reveals the extrinsic type of conduction with donor impurity levels that behave as acceptor levels when are empty. The data analysis allowed the calculation of the hole and the electron effective masses as 0.654m₀ and 0.119m₀, respectively. In addition, the temperature-dependent Hall mobility in the n-region is found to be limited by the electron–phonon short-range interactions scattering with an electron–phonon coupling constant of 0.21.     

H2对UHV/CVD低温选择性外延生长Si1-xGex的影响

利用超高真空化学气相沉积(UHV/CVD)成功实现了Si_1-xGe_x的低温选择性外延生长,并研究了H2对选择性外延生长的影响及其作用机理. 以SiH4和GeH4为反应气源,在开有6mm×6mm窗口氧化硅片上进行Si_1-xGe_x外延层的生长.首先分别以不含H2(纯GeH4)和含H2(90% H2稀释的GeH4)的两种Ge源进行选择性外延生长.通过SEM观察两种情况下氧化硅片表面,发现H2的存在对选择性外延生长有至关重要的作用.接着以90% H2稀释的GeH4为Ge源,变化Si源和Ge源的流量比改变H2分压,以获得SiH4和GeH4 (90% H2）的最佳流量比，使外延生长的选择性达到最好. 利用SEM观察在不同流量比时，经40min外延生长后各样品的表面形貌，并对其进行比较，分析了H2分压在Si_1-xGe_x选择性外延生长中的作用机理.     

Study of SiC and Si3N4 inclusions in industrial multicrystalline silicon ingots grown by directional solidification method

In directional solidification of multicrystalline silicon ingots for solar cells, the concentration of C and N impurities in the silicon melts increases with progression of solidification due to their relatively low segregation coefficients. In the case of supersaturation of C and N in silicon melts, SiC and Si₃N₄ inclusions are formed. In this work, a piece of multicrystalline silicon was selected from a central block, which was cut out from an industrial multicrystalline silicon ingot grown by directional solidification method. The distribution of SiC and Si₃N₄ inclusions from the top to bottom regions was systematically studied. It was found that majority of SiC and Si₃N₄ inclusions are present in the top region and the amount of inclusions decreases exponentially from the top surface down to the bulk of the ingot. Morphologies and characteristics of the SiC and Si₃N₄ inclusions were investigated. The presence of SiC and Si₃N₄ inclusions generates high density of dislocations in multicrystalline silicon, and sometimes can also introduce pores into multicrystalline silicon. The results of this work will be of practical interest to the photovoltaic industry.     

SOI planar photonic crystal fabrication: Etching through SiO2/Si/SiO2 layer systems using fluorocarbon plasmas

Dry plasma etching of sub-micron structures in a SiO₂/Si/SiO₂ layer system using Cr as a mask was performed in a fluorocarbon plasma. It was determined that the best anisotropy could be achieved in the most electropositive plasma. A gas composition yielding the desired SOI planar photonic crystal structures was optimized from the available process gases, Ar, He, O₂, SF₆, CF₄, c-C₄F₈, CHF₃, using DC bias data sets. Application of the c-C₄F₈/(noble gas) chemistry allowed fabrication of the desired SOI planar photonic crystal. The average etching rates for the pores and ridge waveguide regions were about 71 and 97 nm/min, respectively, while the average SiO₂/Si/SiO₂ to Cr etching selectivity for the ridge waveguide region was about 33:1 in case of the c-C₄F₈/90%Ar plasma with optimized parameters.     

Monte Carlo simulation for the sputtering yield of Si3N4 thin film milled by focused ion beams

The sputtering yield of the Si3N4 thin film is calculated by Monte Carlo method with different parameters. The dependences of the sputtering yield on the incident ion energy, the incident angle and the number of Gallium （Ga） and Arsenic （As） ions are predicted. The abnormal sputtering yield for As at 90 keV occurs when the incident angle reaches the range between 82° and 84°.     

CNTs/Fe3O4复合电泳提高CNTs阴极场发射性能

A simple CNT/Fe₃O₄ composite electrophoretic deposition method to improve the field emission cathode properties of carbon nanotubes (CNTs) is proposed. It is found that CNT/Fe₃O₄ composite electrophoretic deposition leads to better field emission performance than that of single CNT electrophoretic deposition. The result is investigated using SEM, J-E and FE. After the process, the turn-on electric field decreases from 0.882 to 0.500 V/μm at an emission current density of 0.1 mA/cm², and the latter increases from 0.003 to 1.137 mA/cm² at an electric field of 0.64 V/μm. CNT/Fe₃O₄ composite electrophoretic deposition is an easy and effective cathode preparation for field emission display applications.     

NH3-Ar气氛下制备的Zn3N2薄膜的结构和光学性能

在NH3-Ar气氛下,用RF磁控溅射金属Zn靶在玻璃衬底上室温制备了Zn3N2薄膜,研究了NH3分压对Zn3N2薄膜的结构和光学特性的影响。XRD分析表明Zn3N2薄膜出现多晶结构,具有(321)择优取向。当NH3分压从5%变化到25%时,Zn3N2薄膜的间接光学带隙从2.33eV升高到2.70eV。室温下Zn3N2薄膜在437nm和459nm波长出现了发光峰,并对发光机理进行了分析。     

SO2-4/Bi2O3固体超酸的制备及其可见光催化性能

采用水热法结合H2SO4浸泡处理成功合成了SO^2-₄/Bi₂O₃可见光催化材料, 并采用XRD、TG DTA和UV Vis等对合成产物的物相结构、热化学性能、光吸收性能以及可见光催化性能进行了研究, 对H2SO4浸泡工艺条件对产物的可见光催化性能的影响进行了探讨。研究表明, 水热合成产物为α-Bi₂O₃、Bi₂O₄和Bi₂O₂CO₃的混合物, 其中α-Bi₂O₃为主要成分;H₂SO₄浸泡处理并未改变产物的物相结构, 但经H₂SO₄浸泡处理后产物的光催化性能得到了显著的提高, 并且H₂SO₄浸泡工艺条件对产物的光催化活性有着重要的影响。在实验范围内, 在浓度为0.5mol·L^-1的H₂SO₄溶液中浸泡75min, 再经700℃热处理4h可制备出具有较佳光催化活性的产物, 经75min可见光的照射后对甲基橙溶液的光催化脱色率可达93.1%。     

共沉淀法制备Y2O2SO4:Eu3+荧光粉及其光致发光研究

采用商业Y(NO3)3·6H2O、Eu(NO3)3·6H2O、(NH4)2SO4和NaOH为实验原料,通过共沉淀法制备了Y2O2SO4:Eu3+荧光粉。利用热分析(DTA-TG-DTG)、傅里叶变换红外(FT-IR)光谱、X射线衍射(XRD)、扫描电子显微镜(SEM)和光致发光(PL)光谱等手段对合成的粉体进行了表征。结果表明,当(NH4)2SO4引入到反应体系中时,前驱体具有非晶态结构,且在空气气氛中800℃煅烧2h能转化为单相的Y2O2SO4粉体,该Y2O2SO4粉体呈准球形,粒径范围分布在0.5~1.0μm之间,团聚较严重。PL光谱分析表明,在270nm紫外光激发下,Y2O2SO4:Eu3+荧光粉呈红光发射,主发射峰位于620nm,归属于Eu3+的5D0→7F2跃迁。Eu3+的猝灭浓度是5 mol%,其对应的荧光寿命为1.22 ms。另外,当(NH4)2SO4未引入到反应体系中时,采用类似的方法合成了Y2O3:Eu3+荧光粉,并对Y2O2SO4:Eu3+和Y2O3:Eu3+荧光粉的PL性能进行了比较。