Improving the edge quality of single-crystal diamond growth by a substrate holder – An analysis

During the growth of a single-crystal diamond by MPCVD, polycrystalline diamonds are prone to grow in the edge regions. This substantially reduces the usable area of the grown diamond film. In addition, the inhomogeneous distribution of internal stress causes diamond to crack during continuous growth. In recent years, a series of experimental studies have been carried out to solve these problems and some achievements have been obtained. However, in order to understand fundamentally the growth mechanism of diamond, the relationship between growth quality and various influencing factors still needs to be quantitatively studied through integrated simulations and experiments. Electron number density and substrate temperature are important factors affecting diamond crystallization quality. In this paper, the growth conditions of the diamond were simulated and analyzed. Simulation results were compared with the experimental results. This evidences that the surface temperature distribution is relatively homogeneous, and that the significant electron number density gradient in the axial direction is the main reason for the formation of polycrystals in the edge regions. Therefore, substrate holders with different cavity depths were designed and the substrates grew in the same temperature range. The surface morphologies, crystalline qualities, and internal stress distributions of the grown diamonds were measured, and it was found that the quality of growth increased first and then decreased with the depth of the cavity, while the growth rate decreased with increasing the latter. These results are in good agreement with the simulation results. Finally, suggestions on the selection of the substrate holder for film growth with different thicknesses are proposed.     

单晶金刚石边缘表面倾斜角度对同质外延生长的影响

利用微波等离子体化学气相沉积法,对单晶金刚石(100)晶面边缘进行精细切割抛光处理,形成偏离(100)晶面不同角度的倾斜面,在CH_4/H_2反应气体中进行同质外延生长,研究单晶金刚石边缘不同角度倾斜面对边缘金刚石外延生长的影响.实验结果表明,边缘倾斜面角度对边缘的单晶外延生长质量有影响,随着单晶金刚石边缘倾斜面角度的增大,边缘多晶金刚石数量先减少后增多,在倾斜角3.8°时边缘呈现完整的单晶外延生长特性.分析认为,边缘不同角度的倾斜面会改变周围电场强度和等离子体密度,导致到达衬底表面的含碳前驱物发生改变,倾斜面台阶表面的含碳前驱物浓度低于能形成层状台阶生长的临界浓度是减弱单晶金刚石生长过程中边缘效应的主要原因.     

Growth and Characterization of the Laterally Enlarged Single Crystal Diamond Grown by Microwave Plasma Chemical Vapor Deposition

Laterally enlarged single crystal diamond is grown on(001) diamond substrates by microwave plasma chemical vapor deposition. Based on the largest side-to-side width of the seed of 7.5 mm, we achieve the as-grown epilayer with the width of about 10 mm between the same two sides. The luminescence difference between the broadened part of the single crystal diamond and the vertically epitaxial part is investigated by characterizing the vertical cross section of the sample, and the possible growth mechanism is suggested. Vertical epitaxy on the top(001)surface and lateral growth on the side surfaces occur simultaneously, and thus the growth fronts along the two directions adjoin and form a coalescence zone extending from the edge of the substrate towards the edge of the expanded single crystal diamond top surface. The luminescence intensity of the nitrogen-vacancy center is relatively high in the coalescence zone and a laterally grown part right below, which are attributed mainly to the higher growth rate. However, stress change and crystal quality change are negligible near the coalescence zone.     

籽晶尺寸对宝石级金刚石单晶生长的影响

本文在国产六面顶压机上,在5.6 GPa, 1250—1450℃的高压高温条件下,分别选用边长0.8, 1.5和2.2 mm三种尺寸的籽晶,系统开展了Ib型宝石级金刚石单晶的生长研究.文中系统考察了籽晶尺寸对宝石级金刚石单晶生长的影响.首先,考察了籽晶尺寸变化对宝石级金刚石单晶裂晶问题带来的影响.研究得到了籽晶尺寸变大,裂晶出现概率增加的晶体生长规律.其次,在25 h的生长时间内,考察了上述三种尺寸籽晶生长金刚石单晶时,生长时间与单晶极限生长速度的关系.得到了选用大尺寸籽晶,可以提高优质单晶合成效率、降低合成成本的研究结论.借助扫描电子显微镜和光学显微镜,对三种尺寸籽晶生长金刚石单晶的表面形貌进行了标定.最后,傅里叶微区红外测试,对三种尺寸籽晶生长宝石级金刚石单晶的N杂质含量进行了表征.研究得到了选用大尺寸籽晶实现快速生长金刚石的同时,晶体的N杂质含量会随之升高的晶体生长规律.     

金刚石层厚度对复合片(PDC)残余应力的影响

 通过X射线应力测试和有限元分析相结合的方法,研究了金刚石层厚度对聚晶金刚石复合片（PDC）残余应力的影响,并根据实验测试结果推导出了PDC表面中心与边缘的应力随金刚石层厚度变化的关系式。随着金刚石层厚度由0.5 mm增加到2.0 mm,PDC表面中心的压应力从1 800 MPa下降至700 MPa左右,而边缘部分的应力逐渐由压应力转为拉应力。金刚石层加厚虽然对边缘部分的最大拉应力影响不大,但使PDC边缘拉应力区宽度由0.76 mm增加到了2.85 mm。金刚石层厚度的增加还使得PDC边缘界面附近y方向的最大拉应力和位于界面边缘处的最大剪应力显著加大,这是金刚石层较厚的PDC界面容易产生裂纹的主要原因。     

高压熔渗生长法制备金刚石聚晶中碳的转化机制研究

在6 GPa和1500 ℃的压力和温度范围内, 利用高压熔渗生长法制备了纯金刚石聚晶, 深入研究了高温高压下金刚石聚晶生长过程中碳的转化机制. 利用光学显微镜、X-射线衍射、场发射扫描电子显微镜检测, 发现在熔渗过程中金刚石层出现了石墨化现象, 在烧结过程中金刚石颗粒表面形貌发生了变化. 根据实验现象分析, 在制备过程中存在三种碳的转化机制: 1)金属熔渗阶段金刚石颗粒表面石墨化产生石墨; 2)产生的石墨在烧结阶段很快转变为填充空隙的金刚石碳; 3)金刚石直接溶解在金属溶液中, 以金刚石形式在颗粒间析出, 填充空隙. 本文研究碳的转化机制为在高温高压金属溶剂法合成金刚石的条件下(6 GPa和1500 ℃的压力和温度范围内)工业批量化制备无添加剂、无空隙的纯金刚石聚晶提供了重要的理论指导.     

温度对Ib型和IIa型金刚石大单晶(100)表面特征的影响

本文在5.6 GPa, 1250–1340 ℃的条件下, 利用温度梯度法, 以FeNiMnCo 合金为触媒, 沿籽晶的(100)晶面成功合成了不同晶形的优质Ib型和IIa型金刚石大单晶. 利用激光拉曼附件显微镜, 分别对上述不同温度下合成的两类金刚石样品上表面(100)面的中心区域及棱角区域进行观察分析. 研究发现, Ib型和IIa型金刚石大单晶(100)晶面上从中心到棱角处黑色纹路的分布逐渐变黑变密集; 另外, 随着金刚石合成温度的升高, Ib型金刚石大单晶(100)面上黑色纹路由稀疏逐渐变稠密, 而IIa型金刚石大单晶的黑色纹路较为稀疏; Ib型金刚石大单晶的形貌特征表现为从低温晶体的不规则分布过渡到中温、高温晶体的典型树枝状分布. IIa型金刚石大单晶(100)面特征随温度变化规律与Ib型的类似. 这两类金刚石大单晶表面特征的差异可能是由于IIa 型金刚石具有比Ib型更小的生长速度和更少的氮含量. 最后, 对两类塔状金刚石大单晶进行拉曼光谱测试分析, 结果表明IIa型金刚石大单晶的品质较Ib型金刚石大单晶好.     

Determination of the thermal conductivity of polycrystalline diamond films by means of the photoacoustic effect

A new method of determining the heat-conducting properties of diamond films is proposed, based on the photoacoustic effect. This method is used to study diamond polycrystalline films grown on silicon by chemical vapor deposition in a microwave discharge plasma. The thermal conductivity obtained was approximately half that for single-crystal diamond. Zh. Tekh. Fiz. 69, 97–101 (April 1999)     

UV detectors based on epitaxial diamond films grown on single-crystal diamond substrates by vapor-phase synthesis

The prospects for use of CVD-technology for epitaxial growth of single-crystal diamond films of instrumental quality in UHF plasma for the production of optoelectronic devices are discussed. A technology for processing diamond single crystals that provides a perfect surface crystal structure with roughness less than 0.5 nm was developed. It was demonstrated that selective UV detectors based on synthetic single-crystal diamond substrates coated with single-crystal films can be produced. A criterion for selecting clean and structurally perfect single crystals of synthetic diamond was developed for the epitaxial growth technology.     

Surface erosion of tungsten and the morphology of erosion products in experiments simulating plasma disruption

The surface erosion of different sorts of tungsten subjected to high-power pulsed plasma streams simulating plasma disruption is studied. With W-13I polycrystalline and (111) single-crystal tungsten samples used as examples, the size distributions for the erosion products collected at different angles to the target are compared. The typical drop erosion of the surface is observed. Fine drops either return to the surface or fly away in a direction parallel to the surface. Coarse drops leave the surface nearly at right angles to the surface. The single-crystal surface displays the absence of fine (<0.125 μm) drops typical of a polycrystalline tungsten surface. The erosion of the single-crystal samples is least among the tungsten sorts considered.     

Study of microwave plasma-assisted chemical vapor deposition of poly-and single-crystalline diamond films

We study conditions for microwave plasma-assisted chemical vapor deposition of high-quality single-crystal diamond films in a CVD reactor. These conditions are studied using the results of homoepitaxial growth of polycrystalline diamond films on diamond substrates and on the basis of numerical simulation of the microwave discharge in a CVD reactor. A high-quality single-crystal diamond layer is synthesized on a synthetic, type Ib diamond substrate. The properties of the obtained monolayer are studied by means of Raman and X-ray diffraction spectroscopy as well as optical and atomic-force microscopy.     

Behavior of the Water-Cooled Polycrystalline Diamond Plate at Extreme Densities of Laser Radiation

Resistance of a water-cooled polycrystalline diamond window is experimentally studied in the beam of the 10-kW fiber laser. The irradiated zones are 4 and 0.4 mm in diameter. It is shown that the transmitted beam is not distorted when the power density increases to 7 MW cm^?2. It is found out that the temperature difference of a few hundreds of degrees between the center of the diamond window and its water-cooled edge does not deteriorate the distribution quality of the laser beam transmitted through the window, which allows the arising thermal lens to be corrected.     

富勒烯作为过渡层生长金刚石薄膜研究

采用微波等离子体化学气相淀积法，以Ｃ６０膜过渡层，在光滑的单晶Ｓｉ衬底（１００）表面的研磨的石英衬底表面等光学衬底上，首次在无衬底负偏压条件下生长出多晶金刚石薄膜，通过扫描电镜观察到生长膜晶粒呈莱花状，生长表面为金刚石（１００）界面。     

High quality CVD diamond: a Raman scattering and photoluminescence study

High quality synthetic diamonds were grown on single-crystal silicon by microwave plasma enhanced chemical vapour deposition (CVD). A careful optimisation of both the experimental setup and the growth parameters was necessary before that the achievement of the best results was made possible. The films were deposited using a CH₄-H₂ gas mixture at methane concentrations variable in the range 0.6-2.2%, while the substrate temperature was fixed at 750 ^°C. Raman spectroscopy and photoluminescence (PL) were utilised to monitor the quality of the deposited films and to study the spatial distribution of defects, respectively. Micro-Raman analysis shows that linewidths of the diamond peak lower than 2.4 cm^-1 can be easily measured at the growth surface, indicating that the crystalline quality of individual grains is comparable to that of the best natural diamonds. The excellent phase purity of the diamond microcrystals at the growth surface is witnessed by the complete absence of any non-diamond carbon feature and by a very weak luminescence background in the 1.6-2.4 eV spectral range. A worsening of the quality of the diamond particles is found moving from the growth surface towards the film-substrate interface. A photoluminescence feature at about 1.68 eV, commonly associated to Si impurities, is distinctly observed as the exciting laser beam is focused close to the interface. A progressive degradation of the global quality of the films is found with increasing methane concentration in the gas mixture, as witnessed by an increased PL background in the films grown at higher methane concentrations. Received 24 November 2000     

不同晶面的氢终端单晶金刚石场效应晶体管特性

通过微波等离子体化学气相淀积技术生长单晶金刚石并切割得到(110)和(111)晶面金刚石片,以同批器件工艺制备两种晶面上栅长为6μm的氢终端单晶金刚石场效应管,从材料和器件特性两方面对两种晶面金刚石进行对比分析.(110)面和(111)面金刚石的表面形貌在氢终端处理后显著不同,光学性质则彼此相似.VGS=–4 V时,(111)金刚石器件获得的最大饱和电流为80.41 m A/mm,约为(110)金刚石器件的1.4倍;其导通电阻为48.51 W·mm,只有(110)金刚石器件导通电阻的67%.通过对器件电容-电压特性曲线的分析得到,(111)金刚石器件沟道中最大载流子密度与(110)金刚石器件差异不大.分析认为,(111)金刚石器件获得更高饱和电流和更低导通电阻,应归因于较低的方阻.     

考虑相界效应的Ni基单晶合金纳米压痕模拟

利用分子动力学方法分别模拟金刚石压头压入Ni模型和Ni基单晶合金γ/γ′模型的纳米压痕过程,通过计算得到两种模型[001]晶向的弹性模量及硬度.采用中心对称参数分析不同压入深度时两种模型内部位错形核、长大过程以及Ni基单晶合金γ/γ′(001)相界面错配位错对纳米压痕过程的影响.结果显示:压入深度0.641 nm之前,两种模型的压入载荷-压入深度曲线相似,说明此时相界面处的错配位错对纳米压痕过程的影响很小;压入深度0.995 nm时,在错配位错处发生位错形核,晶体在γ相中沿着{111}面滑移,随即导致Ni基单晶合金γ/γ′模型压入载荷的下降,并在压入深度达到1.487 nm之前低于Ni模型相同压入深度时的压入载荷;压入深度从1.307 nm开始,由于相界面错配位错的阻碍作用,Ni基单晶合金γ/γ′模型压入载荷上升速度较快.     

山东蒙阴金刚石多晶的显微红外光谱研究及其成因意义

山东蒙阴金刚石多晶可划分为多角刻面状和浑圆状金刚石多晶两大类,它们的显微红外光谱研究结果表明,金刚石多晶中的氮含量较低,介于16.69～72.81μg.g-1之间,且同一金刚石多晶的不同金刚石晶粒(或部位)中的氮含量不相同;刻面状金刚石多晶均为ⅠaAB型,且A心的浓度大于B心的浓度。浑圆状金刚石多晶也多为ⅠaAB型,但具有更高浓度的B心,且存在少数同时包含单替代氮、A心和B心的浑圆状金刚石多晶;金刚石多晶不是在金刚石颗粒的成核阶段所形成的,而是在金刚石长大期间或金刚石颗粒形成后的某个特殊条件下聚集而成;山东蒙阴金刚石多晶可能形成于氮浓度较低的较深部地幔。同时,多角刻面状金刚石多晶的形成时间稍晚于金刚石单晶体,浑圆状金刚石多晶的形成时间明显早于金刚石单晶体。     

ZnO薄膜/金刚石在不同激励条件下声表面波特性的计算与分析

本文首先以刚度矩阵法为基础, 给出了ZnO薄膜/金刚石在四种不同激励条件下的有效介电常数计算公式. 然后以此为工具, 分别计算了多晶ZnO(002) 薄膜/多晶金刚石和单晶ZnO(002) 薄膜/多晶金刚石的声表面波特性, 并根据计算结果及设计制作声表面波器件的要求, 对ZnO膜厚的选择进行了详细地分析. 最后讨论了ZnO/金刚石/Si复合晶片可以忽略Si衬底对声表面特性影响时对金刚石膜厚的要求. 关键词： 声表面波 压电多层结构 有效介电常数 刚度矩阵法     

What is the ground-state structure of the thinnest Si nanowires?

Pristine silicon whiskers are compared through energy analysis by separating the surface, edge, and bulk contributions, and by energy computation for a variety of structures and diameters d. It is shown that for d<6 nm a polycrystalline wire of five-fold symmetry, rather than single-crystal types, represents the ground state. It remains stable in molecular dynamics tests up to approximately 1000 K. Its specific surface reconstruction also stands out in that it favors kinetics of whisker growth and thus appears potentially realizable.     

Field-emission diodes based on semiconductor—polycrystalline diamond heterojunctions

A complex of electrophysical and technological studies of solid-state field-emission diodes is carried out. Emission comes from an array of nanometer objects near the semiconductor—polycrystalline diamond interface. The process route of the diode heterostructures includes the fabrication of nanometer masks and nanometer cone (tip) arrays, as well as plasma-assisted growth of polycrystalline diamond films on the surface of structures with nanometer cone arrays. In field-emission diodes thus formed, a current density as high as 20 A/cm² is achieved at a threshold of field emission from the nanotip arrays into the diamond of about 0.5 V.