注C+外延硅的光致发光特性

在N型外延硅中注入C+并经高温退火形成了SiC沉积.不同条件下进行阳极氧化腐蚀后,在260nm光激发下获得了340nm和430nm的紫外和紫光峰,它们的单色性很好,半高宽(FWHM)约为10nm.在以上条件下SiC沉积并未多孔化,认为340nm和430nm峰可能源于样品中的C、O杂质镶嵌于纳米硅表面所形成的发光中心.讨论了各种发光中心形成的可能条件,并对实验结果做出了初步解释.     

EA-HFCVD 沉积纳米金刚石膜的光致发光分析

采用电子辅助-热丝化学气相沉积法(EA-HFCVD)在硅片上沉积出晶粒尺寸为30nm的均匀金刚石膜。生长过程中,预先加6A偏流生长1h,然后在0.8kPa条件下,无偏流生长3h。光致发光谱中存在4个发光中心分别位于1.682eV,1,564eV,1,518eV和1.512eV的发光峰。1.682eV处发光峰源于衬底硅原子掺杂于膜中引起的缺陷;其他发光峰源于金刚石晶格振动声子。光致发光强度越大对应的缺陷密度越大,从而降低了场发射域值电场强度,其关键可能源于金刚石膜电导型晶界。     

α-SiO_xN_y薄膜中分立能级的光发射

采用 PECVD法制备了 α- Si Ox Ny 薄膜 ,观察到两组分立能级的强荧光发射 ,一组位于紫外光波段 ,由三个可分辨的发射峰组成 ,波长分别为 330、340和 345nm;另一组位于红光波段 ,由两个发射峰组成 ,波长分别为 735nm和 745nm.发射峰依赖于薄膜中氧和氮的同时存在 ,其强度首先随薄膜中其含量的增加而增强 ,达到饱和值后 ,随着其含量的进一步增加而下降 .这表明发射峰可能起源于 O- Si- N结合而形成的发光中心 .     

自催化方式制备ZnO纳米线及光致发光特性

采用化学气相沉积法,不用催化剂,在Si(111)基片上制备了ZnO纳米线。扫描电子显微镜(SEM)表征发现ZnO纳米线的直径在100nm左右。X射线衍射(XRD)图谱上只存在ZnO的(002)衍射峰。室温下光致发光谱(PL)中出现了389nm和357nm的紫外峰以及五个蓝光峰(450,468,474,481和491nm)。389nm峰为自由激子复合发射357nm峰是在LO声子的参与下,自由载流子碰撞形成自由激子过程的发光行为;468nm峰系电子从氧空位形成的浅施主能级向价带跃迁发光;450nm峰系电子从导带向锌空位形成的浅受主能级跃迁发光;474,481和491nm峰是声子伴线。     

Si/SiO2和SiNx/SiO2多层膜的室温光致发光

采用射频磁控溅射法,制备了纳米Si/SiO2和SiNx/SiO2多层膜,得到强的可见光致发光,利用傅里叶红外吸收(FTIR)谱和光致发光(PL)谱,对其发光特性进行了研究,在374 nm和712 nm左右观察到强发光峰.用量子限制-发光中心(QCLC)模型解释了其可能的发光机制,认为发光可能源自于SiOx界面处的缺陷发光中心.建立了发光的能隙态(EGS)模型,认为440 nm和485 nm的发光源于N-Si-O和Si-O-Si缺陷态能级.     

退火对富硅氮化硅薄膜的结构和发光的影响

采用等离子体增强化学气相沉积方法(PECVD)，在低衬底温度下制备了富硅氮化硅薄膜。利用红外吸收谱(IR)、XPS光电子能谱和光致发光谱(PL)，研究了不同的退火温度对薄膜结构和发光的影响。研究发现，薄膜经退火后，在发光谱中出现一强的发光峰。当经过900℃退火后，随着与硅悬键有关的发光峰的消失．该强的主发光峰发生了明显的蓝移，并且有所宽化。蓝移现象源于高温退火后，在薄膜中有小尺寸的Si团簇形成。通过实验结果分析，提出薄膜的发光起因于包埋在氮化硅中的Si团簇。     

纳米硅量子点/氮化硅三明治结构的电致发光

采用等离子体化学气相沉积技术制备了两种不同非晶硅层厚度的氮化硅/氢化非晶硅/氮化硅三明治结构,研究了不同能量激光退火对薄膜晶化的影响。通过拉曼分析,发现在激光能量为320mJ时,样品开始晶化,随着能量的提高晶化程度增加,在340mJ时达到最大。根据拉曼晶化峰的偏移,计算得出硅量子点尺寸为2.8nm和4.7nm,表明三明治结构对形成的硅量子点的尺寸具有限制作用。设计并制备了基于该结构的电致发光器件,在偏压大于10V时,在室温下可观测到电致发光。发现不同激光能量下晶化后的样品的电致发光强度不同,发光峰位在680nm和720nm附近。分析表明电致发光来源可以归结为电子空穴对在硅量子点中的辐射复合发光。     

ZnS/PS复合体系的光致发光特性研究

通过电化学阳极氧化法制备了多孔硅（porous Si,PS）样品,然后用脉冲激光沉积的方法在其上沉积ZnS薄膜,并测量了ZnS/PS复合体系的光致发光谱,结果表明,在不同的激发波长（340nm,360nm,390nm）下,ZnS/PS复合体系的光致发光谱不同,ZnS和PS发光的相对（蓝/红）积分强度比值也不同;ZnS薄膜的生长温度不同（100℃,250℃,350℃）时,ZnS/PS复合体系的发光不同,随着生长温度的升高,复合体系的发光谱中,ZnS的发光增强而PS的发光减弱;衬底PS的制备电流密度不同（3mA/cm2,9mA/cm2,11mA/cm2）时,ZnS/PS复合体系的发光也有着不同的特点,在适当的PS制备电流密度条件下,把ZnS的发光与PS的发光叠加,得到了可见光区较宽的光致发光谱带（450nm～700nm）,呈现较强的白光发射。     

硫化锌／多孔硅复合体系光致发光特性的研究

为了研究硫化锌／多孔硅复合体系的光致发光特性,通过电化学阳极氧化法制备了多孔硅样品,然后用脉冲激光沉积的方法在其上沉积硫化锌薄膜,测量了硫化锌／多孔硅复合体系的光致发光谱,并对其进行了详细的理论分析和实验验证。结果表明,在不同的激发波长(340nm,360nm,390nm)下,硫化锌／多孔硅复合体系的光致发光谱不同,硫化锌和多孔硅发光的相对(蓝／红)积分强度比值也不同;硫化锌薄膜的生长温度不同(100℃,250℃,350℃)时,硫化锌／多孔硅复合体系的发光不同,随着生长温度的升高,复合体系的发光谱中,硫化锌的发光增强而多孔硅的发光减弱;衬底多孔硅的制备电流密度不同(3mA／cm²,9mA／cm²,11mA／cm²)时,硫化锌／多孔硅复合体系的发光也有着不同的特点。在适当的多孔硅制备电流密度条件下,把硫化锌的发光与多孔硅的发光叠加,得到了可见光区较宽的光致发光谱带(450nm～700nm),呈现较强的白光发射,这一结果为白光二极管的实现开辟了一条新的捷径。     

纳米硅镶嵌氮化硅薄膜的制备与光致发光特性

为研究氮化硅薄膜发光材料的制备工艺及其光致发光机制,实验采用射频磁控反应溅射技术与热退火处理制备了纳米硅镶嵌氮化硅薄膜材料.利用红外光谱(IR)、X射线衍射谱(XRD)、能谱(EDS)和光致发光谱(PL),对不同工艺条件下薄膜样品的成分、结构和发光特性进行研究,发现在制备的富硅氮化硅薄膜材料中形成了纳米硅颗粒,并计算出其平均尺寸.在510 nm光激发下,观察到纳米硅发光峰,对样品发光机制进行了讨论,认为其较强的发光起因于缺陷态和纳米硅发光.     

Formation of nickel disilicide using nickel implantation and rapid thermal annealing

Transmission electron microscopy (TEM), secondary ion mass spectroscopy (SIMS), and x-ray photoemission spectroscopy (XPS) have been used to investigate the nucleation, growth, and ripening behavior of nickel-disilicide precipitates formed by Ni implantation in an amorphous-Si layer on (100) Si and followed by a two-step annealing treatment. The TEM and XPS results show that amorphous-disilicide precipitates are formed in a depth of ∼21 nm in the amorphous-Si layer when pre-annealed at 380°C for 30 sec. It is also shown that the second-step annealing at temperatures in the range of 450–600°C causes the amorphous precipitates to transform to randomly oriented crystalline ones embedded in the amorphous-Si layer. Annealing above 550°C is shown to induce the crystallization of amorphous Si by solid-phase epitaxial growth (SPEG). It is further shown that, in a prolonged annealing at high temperatures, the disilicide has dissolved and reprecipitated on the Si surface. Based on the roles of the silicide-mediated crystallization (SMC), the dissolution and reprecipitation of silicides, and SPEG, possible mechanisms are given to explain how the surface-disilicide islands are formed during annealing at temperatures of 550–950°C.     

SiC/Mg multilayer reflective mirror for He-Ⅱ radiation at 30.4 nm and its thermal stability

In applications of solar physics, extreme ultraviolet imaging of solar corona by selecting the HeⅡ (λ = 30.4 nm) emission line requires high reflectivity multilayer mirrors. Some material combinations were studied to design the mirrors working at a wavelength of 30.4 nm, including SiC/Mg, B4C/Mg, C/Mg, C/Al, Mo/ Si, B4C/Si, SiC/Si, C/Si, and Sc/Si. Based on optimization of the largest reflectivity and the narrowest width for the multilayer mirror, a SiC/Mg material combination was selected as the mirror and fabricated by a magnetron sputtering system. The layer thicknesses of the SiC/Mg multilayer were measured by an X-ray diffractometer. Reflectivities were then measured on beamline U27 at the National Synchrotron Radiation Laboratory (NSRL) in Hefei, China. At a wavelength of 30.4 nm, the measured reflectivity is as high as 38.0%. Furthermore, a series of annealing experiments were performed to investigate the thermal stability of the SiC/Mg multilayer.     

Cr掺杂SiC薄膜的制备与光致发光特性

利用高纯SiC烧结靶上粘贴金属Cr片的复合靶用双离子束溅射沉积方法,在Si和KBr单晶衬底上制备了掺杂SiC薄膜。用傅里叶变换红外光谱分析法(FTIR)和喇曼光谱仪对制得的薄膜样品进行了表征,用荧光分光光度计对样品的光致发光(PL)特性进行了研究。通过FTIR分析得到对应于Si―C键的峰位没有发生明显改变而峰强随着Cr掺杂量的增加而降低,喇曼光谱分析发现Cr掺杂导致Si和C团簇的形成,说明Cr的掺杂阻碍了Si―C键的结合。将不同Cr掺杂浓度的SiC薄膜经1000℃退火处理,发现位于413、451和469nm的三个发光峰的位置基本不变,但强度有明显改变。     

SiC/Si(111) film quality as a function of GeH4 flow in an MOCVD reactor

Due to large lattice and thermal expansion coefficient mismatches, SiC films grown on Si are usually low quality. To provide a more stable growth front we added Ge in the form of GeH₄ to the reactant gases in a MOCVD reactor. Several SiC films with Ge flow rates ranging from 0–50 sccm were grown on (111) Si substrates at 1000°C. TEM results show that the crystalline quality is amorphous or polycrystalline for Ge flow rates at or below 15 sccm. Samples grown at Ge flow rates at or exceeding 20 sccm have an initial layer of single crystalline 3C SiC followed by heavily twinned crystalline 3C SiC. In particular, the samples grown with 20–30 sccm Ge contain an 80 nm initial layer of reasonably high quality single crystal 3C SiC.     

CW blue-green light emission from GaN and SiC by sum-frequency generation and second harmonic generation

Continuous wave (CW) back-scattered sum-frequency generation (SFG) and second harmonic generation (SHG) have been obtained from GaN and SiC. GaN samples were obtained from GaN films grown by molecular-beam epitaxy (MBE), metalorganic chemical-vapor deposition and hydride vapor-phase epitaxy. The SiC samples were obtained from 3C SiC/Si grown by chemical vapor deposition (CVD), 4H and 6H single crystal SiC substrates. The samples were optically excited with two CW lasers at the red (840 nm) and the infrared (1.0 μm). SHG at 420 nm and 500 nm and SFG at 455 nm were observed. SFG and SHG were verified by measuring their relative intensities against the pumping laser power. The SHG signals from GaN and SiC samples are compared with that from KH₂PO₄ (KDP).     

Investigation of Co/SiC interface reaction

Interface reaction, phase transition, and composition were investigated for Co thin films on amorphous SiC films as a function of heat treatment (600～1000°C). Amorphous SiC layers were grown on (001) Si substrate by magnetron sputter deposition. The SiC layers had a 1:1 stoichiometric ratio of Si to C and an amorphous structure containing microcrystals. The interface reaction between a sputter-deposited Co (250Å thick) and amorphous SiC (2000Å thick) layer on a (001) Si substrate induced by vacuum annealing at temperatures of 600–1000°C was examined. Co₂Si was formed at 700°C as the first crystalline phase and CoSi at 800°C as the final stable phase of the Co/SiC interface reaction. This phase sequence of Co₂Si→CoSi was interpreted in terms of the effective heat of formation and the calculated ternary Co-Si-C phase diagram, and it was consistent with the experimental results. The high formation temperature of the first crystalline Co₂Si phase and no formation of a final stable CoSi₂ phase are discussed in comparison with Co/Si interface reaction and related to the binding energy of the reacting materials. In addition, the behavior of free carbon remaining after the Co/SiC reaction was investigated. This free carbon moved to the top of the reacted cobalt silicide/SiC layer.     

nc-SiC/SiO_2镶嵌薄膜材料的制备、结构和发光特性

采用二氧化硅/碳化硅复合靶,用射频磁控共溅射技术和后高温退火的方法在Si(111)衬底上制备了碳化硅纳米颗粒/二氧化硅基质(nc-SiC/SiO2)镶嵌结构薄膜材料。用X射线衍射(XRD),傅里叶红外吸收(FTIR),扫描电子显微镜(SEM)和光致发光(PL)实验分析了薄膜的微结构以及光致发光特性。实验结果表明,样品薄膜经高温退火后,部分无定形SiC发生晶化,形成β-SiC纳米颗粒而较均匀地镶嵌在SiO2基质中。以280nm波长光激发薄膜表面,有较强的365nm的紫外光发射以及458nm和490nm处的蓝光发射,其发光强度随退火温度的升高显著增强,发光归结为薄膜中与Si—O相关的缺陷形成的发光中心。     

The microstructural analysis of SiC nanorods by high-resolution electron microscopy

Beta-SiC nanorods have been synthesized by the reaction of SiO and carbon nano-capsules. For the synthesis of SiC nanorods, it was examined that the reaction temperature and the ratio of SiO to carbon nanocapsules are important and the most appropriate temperature and ratio are around 1380 degreesC and 5:2, respectively. The synthesized SiC nanorods were characterized by high-resolution electron microscopy. Most of the SiC nanorods are straight and have the diameter of 30-150 nm while the SiC tips of the SiC nanorods have the size 100-400 nm. The SiC nanorods have many stacking faults normal to the [111] direction. Each SiC nanorod has one kind of preferential axis direction, which is either parallel or normal to the [111] direction. Based on the microstructural analysis of the SiC nanorods, a possible growth mechanism of the SiC nanorods is proposed.     

A Vapor–Liquid–Solid Mechanism for Growing 3C‐SiC Single‐Domain Layers on 6H‐SiC(0001)

Growing device‐quality 3C‐SiC monocrystalline material is still an issue despite two decades of work dedicated to the subject. Using silicon as the substrate generates too many defects in the layers, owing to lattice mismatch, while it is very difficult to control the initial nucleation on an α‐SiC substrate so that 60° rotated domains are randomly formed. Herein, the elaboration of mono‐orientated 3C‐SiC layers on a 6H‐SiC(0001) on‐axis, Si face substrate using a vapor–liquid–solid mechanism is reported. This non‐conventional approach for growing monocrystalline layers involves feeding a Ge–Si melt by a propane flux at a temperature ranging from 1250 to 1550 °C. We show that, by using this technique, the 3C‐SiC material is almost always obtained on an hexagonal substrate, even if the crystal seed is oriented 8° off‐axis. Using on‐axis 6H‐SiC seeds and optimal growth conditions results in the reproducible deposition of single‐domain 3C‐SiC layers. A mechanism is proposed to clarify some aspects of this process.     

Study on ta diffusion barrier in Al/Si system

The property of Ta as a diffusion barrier is studied for Al/Ta/Si structure. Interfacial reactions of Al(180 nm)/Ta(130 nm)/Si and Al(180 nm)/Ta(24 nm)/Si, in the temperature range 450∼600°C for 30 min, have been investigated. In Al/Ta(130 nm)/Si system, which is Ta-excess case, Al₃Ta is formed at 500°C. At 575°C, TaSi₂ is formed at the interface of Ta Si. At 600°C, after Al₃Ta decomposes at the interface of Al₃Ta TaSi₂, free Ta is bonded to TaSi₂ with the supply of Si from Si substrate and free Al diffuses through TaSi₂, resulting in Al spiking. In Al/Ta(24 nm)/Si system, which is Al-excess case, Al₃Ta is formed at 500°C. At the same temperature of 500°C, after Al₃Ta decomposes at the interface of Al₃Ta/Si, free Ta reacts with Si to form TaSi₂ and free Al diffuses to Si substrate, resulting in Al spiking. The results of interfacial reactions can be understood from the calculated Al-Si-Ta ternary phase diagram. It can be concluded that the reaction at Al/Ta should be suppressed to improve the performance of Ta diffusion barrier in Al/Si system.