金刚石在太赫兹电真空器件中的应用

金刚石材料具有低的介电常数、小的微波损耗、良好的导热性能,成为太赫兹电真空器件发展过程中非常有研究价值和应用价值的材料。它可以作为输能窗的介质窗片和高频结构的介质支撑材料。本文介绍了微波等离子体化学气相沉积(MPCVD)金刚石材料在太赫兹电真空器件中的具体应用实例,以及在W波段行波管中的实际应用情况,包括MPCVD金刚石的制备过程,及其与金属材料的封接工艺。研制出的W波段金刚石窗冷测结果显示其在75 GHz-110 GHz频段内性能良好:驻波系数(VSWR)≤1.5,传输损耗≤0.5 dB。这种窗已经成功用于W波段折叠波导连续波与脉冲行波管中。     

MPCVD生长半导体金刚石材料的研究现状北大核心

简要介绍了半导体金刚石材料优异的电学和光学性质、主要制备方法以及采用微波等离子体化学气相沉积(MPCVD)技术在制备高质量半导体金刚石材料方面的优势。重点就MPCVD技术在半导体金刚石材料的高速率生长、大尺寸生长、高质量生长以及电学掺杂等四个方面的研究现状进行了详细总结。详细探讨了目前半导体金刚石材料在大尺寸单晶金刚石衬底制备、高质量单晶金刚石外延层生长以及金刚石电学掺杂等方面还存在的一些基本问题。指出在大面积单晶金刚石衬底还没有实现突破的情况下,半导体金刚石材料和器件结构的生长模式。     

微波功率和反应腔室压强对MPCVD生长AlN薄膜质量的影响

研究了微波功率和反应腔室压强对微波等离子体化学气相沉积(MPCVD)法生长AlN薄膜质量的影响。采用高温MPCVD法,以N₂为氮源,三甲基铝(TMAl)为铝源,在6H-SiC衬底上进行AlN薄膜的外延生长。在不同微波功率和不同反应腔室压强下,外延生长了AlN薄膜样品。生长样品的测试结果表明,在微波功率为4 500 W时,样品(002)面X射线摇摆曲线(XRC)半高全宽(FWHM)为217 arcsec。在反应腔室压强为130 Torr(1 Torr=133.3 Pa)时,样品(002)面XRC的FWHM为216 arcsec。该研究将为以后AlN材料的MPCVD生长提供一些参考。     

微波等离子体化学气相沉积法制备C_3N_4薄膜的研究

本文采用微波等离子体化学气相沉积法(MPCVD),高纯N2(99.999%)和CH4(99.9%)作反应气体,在多晶Pt(99.99%)基片上沉积C3N4薄膜。X-射线能谱(EDX)分析结果表明N/C原子比为1.0～1.4,接近C3N4的化学比;X射线衍射谱说明薄膜主要由β和α-C3N4组成;FT-IR谱和Raman谱支持C-N键的存在。     

基片预处理工艺对CVD金刚石成核行为的影响

本文采用微波等离子体辅助化学气相沉积工艺,对不同预处理的(100)单晶硅基片上金刚石的成核行为进行了初步研究,并利用定量金相及扫描电子显微镜分析了金刚石的成核速率及晶体特征。由此提出了用0.1μm超细金刚石粉对基片的研磨工艺。该工艺可有效提高金刚石成核率,从而有助于获得晶粒细小均匀,表面粗糙度低的金刚石薄膜。采用C60涂复并结合研磨工艺,使成核率获得了进一步提高。     

SAW器件用金刚石膜的制备工艺研究

针对声表面波( SAW)器件对金刚石膜的要求,采用石英钟罩式微波等离子体化学气相沉积(MPCVD)装置,研究了不同气体体系对金刚石膜生长速率、电阻率、表面形貌、表层C化合态及相对含量(粒子数分数Xc)的影响.结果表明:在H2-CH3COCH3、CH4-H2-Ar和CH4-H2-N2三种气体体系下,金刚石膜的生长速率分别...     

微米金刚石薄膜的制备与场发射研究

利用微波等离子体化学气相沉积（MPCVD）法,在镀金属钛层的陶瓷基底上面,调整优化沉积参数,制备出了碳膜。通过各种仪器分析了碳膜的内部结构和表面形貌,证明该碳膜是微米金刚石薄膜。进一步将微米金刚石薄膜作为场发射阴极材料,测试了其场致电子发射特性。稳定发射状态下的开启电场为1.15V/μm, 在3.35V/μm的电场下,其场发射电流密度为0.81mA/cm2,发射点密度约为104/ cm2。并对其发射机理进行了研究。     

磁镜场在直接耦合式微波等离子体化学气相沉积金刚石膜制备装置中的应用

在直接耦合式微波等离子体化学气相沉积金刚石膜装置的石英管反应腔加上磁镜场来更好地约束等离子体,使等离子体球成为“碟盘”状,提高了等离子体球的密度,在基本参数：反应压力2．5kPa、基片温度450℃、气体流量为Ar：40sccm、CH4：4sccm、Hz：60sccm不变的情况下,沉积面积直径由30mm增长到50mm,沉积速度由3．3μm／h增长到3．8μm／h,最大反射电流由15μA减小5μA。从而大大减少了在石英管壁和观察窗的沉积,有效利用微波能量电离出更多的活性基团沉积出高质量的（类）金刚石薄膜。     

微波等离子体化学气相沉积法制备C3N4薄膜的研究

本文采用微波等离子体化学气相沉积法（ＭＰＣＶＤ）,高纯Ｎ２（９９．９９９％）和ＣＨ４（９９．９％）作反应气体,在多晶Ｐｔ（９９．９９％）基片上沉积Ｃ３Ｎ４薄膜。Ｘ－射线能谱（ＥＤＸ）分析结果表明Ｎ／Ｃ原子比为１．０～１．４,接近Ｃ３Ｎ４的化学比;Ｘ射线衍射谱说明薄膜主要由β和α－Ｃ３Ｎ４组成;ＦＴ－ＩＲ谱和Ｒａｍａｎ谱支持Ｃ－Ｎ键的存在。     

管道式固体材料微波加热装置的仿真设计*

为了解决工业上固体材料在微波加热过程中普遍存在的能量不集中、效率低、加热不均匀的问题,提 出了一种管道式固体材料微波加热装置的设计方案。利用多物理场仿真对固体材料微波加热均匀性影响因素进行 分析,并优化了微波馈入装置的分布和管道结构,仿真表明该装置具有较好的加热均匀性和较高的效率。基于优化 后的设计,计算了褐煤在微波加热时的温度分布情况,其温度场的变异系数COV 值达到0.166,表明温度分布具有 良好的均匀性。该装置实现了对褐煤的微波均匀加热,对固体材料微波加热的工业应用具有指导意义。     

Growth and Isolation of Large Area Boron‐Doped Nanocrystalline Diamond Sheets: A Route toward Diamond‐on‐Graphene Heterojunction

Many material device applications would benefit from thin diamond coatings, but current growth techniques, such as chemical vapor deposition (CVD) or atomic layer deposition require high substrate and gas‐phase temperatures that would destroy the device being coated. The development of freestanding, thin boron‐doped diamond nanosheets grown on tantalum foil substrates via microwave plasma‐assisted CVD is reported. These diamond sheets (measuring up to 4 × 5 mm in planar area, and 300–600 nm in thickness) are removed from the substrate using mechanical exfoliation and then transferred to other substrates, including Si/SiO₂ and graphene. The electronic properties of the resulting diamond nanosheets and their dependence on the free‐standing growth, the mechanical exfoliation and transfer processes, and ultimately on their composition are characterized. To validate this, a prototypical diamond nanosheet–graphene field effect transistor‐like (DNGfet) device is developed and its electronic transport properties are studied as a function of temperature. The resulting DNGfet device exhibits thermally activated transport (thermionic conductance) above 50 K. Below 50 K a transition to variable range hopping is observed. These findings demonstrate the first step towards a low‐temperature diamond‐based transistor.     

金刚石电子器件的研究进展

简述了金刚石半导体电气性质,即高击穿电场、宽带隙、高载流子饱和速度、高载流子迁移率和高热导率。回顾了金刚石器件的研究进程。讨论了器件的工作机理,包括掺杂和空穴积累层。详细描述了几种具有潜力的金刚石电子器件,如高压二极管和功率场效应管。尽管金刚石器件研究仍存在一些问题,如掺杂机理复杂,金刚石的单晶尺寸太小等,严重制约金刚石电子的进展,但是由于金刚石是超高功率和高温器件的优良半导体材料,具有替代行波管技术的潜力。当前,CVD金刚石已经大量用于微电子和光电子,包括激光二极管、微波器件、半导体散热器等。     

High performance InP JFETs grown by MOCVD using tertiarybutylphosphine

Indium phosphide channel junction field effect transistors were fabricated by metalorganic chemical vapor deposition using tertiarybulylphosphine (TBP) as the alternative source for phosphine. At growth temperatures of 600°C, InP with specular surface morphology and mobilities as high as 61000 cm₂/V s at 77Khas been achieved using trimethylindium and TBP. To improve device isolation, pinch-off characteristics, and output transconductance, we employ a high resistivity (1 × 10⁸ Ω-cm) semi-insulating InP buffer layer using ferrocene as the Fe-dopant. Devices with gate lengths of 1 urn exhibit very high extrinsic transconductance of 130 mS/mm, gate-drain breakdown voltage exceeding 20 V, maximum current density of >450 mA/mm with record high f_T and f_max of 15 GHz and 35 GHz, respectively. These results indicate: that InP JFETs are promising electronic devices for microwave power amplification, and that TBP is capable of device quality materials.     

两种微米金刚石聚晶颗粒薄膜的制备与场发射研究

采用微波等离子体化学气相沉积,在不同的沉积条件下得到两种微米金刚石颗粒薄膜,通过拉曼光谱仪和X射线仪分析了两种薄膜的成分,用扫描电子显微镜分析了两种薄膜的表面形貌,用二级结构的场发射装置研究了薄膜的场发射性能,最终分析并讨论了场发射性能优异的微米金刚石薄膜的特征。     

4H-SiC MESFET工艺中的高温氧化及介质淀积技术

采用自主开发的4H-SiC高温氧化技术,并结合低压化学气相淀积方法,在器件表面形成较为致密的氧化层,降低了器件的反向泄漏电流,提高了器件的击穿电压,同时也提高了器件的输出功率及功率增益,为器件长期稳定可靠工作奠定了工艺基础。采用此技术后,单胞20 mm左右栅宽器件在2 GHz脉冲条件下(脉冲宽度300μs,占空比10%)输出功率达78 W,比原工艺的器件输出功率提高了20 W以上,功率增益提高了1.5 dB,达到8.9 dB左右,功率附加效率也从23%提升到32%,初步显示了该工艺技术在制备4H-SiC微波功率器件中的优势。     

Molecular view of diamond CVD growth

In this paper, we discuss the simulation of the chemical vapor deposition (CVD) of diamond films on the molecular scale. These simulations are performed using a kinetic Monte Carlo method that combines the surface chemistry that is important to diamond growth with an atomic-scale picture of the diamond surface and its evolving atomic structure and morphology. We address the determination of surface reaction kinetics and growth conditions from experiments and reactor-scale models, and the prediction of polycrystalline film texture and morphology from the molecular-scale results. The growth rates and the concentrations of incorporated point defects as a function of substrate temperature for {100}- and {111}-oriented diamond films are obtained from the molecular-scale growth simulations. The {100} growth rates increase with temperature up to 1200K and then decrease above this value. The {111} growth rates increase with temperature at all of the temperatures studied. The concentrations of point defects in the {100} and {111} films are low at substrate temperatures below 1200K, but increase substantially at higher temperatures. The growth efficiency, measured as the ratio of film growth rate to defect concentration, is maximum between 1100–1200K for both film orientations, suggesting that this temperature range is ideal for CVD diamond growth under the simulated growth conditions.     

The role of the low temperature buffer layer and layer thickness in the optimization of OMVPE growth of GaN on sapphire

In agreement with previous work,¹² a thin, low temperature GaN buffer layer, that is used to initiate OMVPE growth of GaN growth on sapphire, is shown to play a critical role in determining the surface morphology of the main GaN epilayer. X-ray analysis shows that the mosaicity of the main GaN epilayer continues to improve even after several μm of epitaxy. This continuing improvement in crystal perfection correlates with an improvement in Hall mobility for thicker samples. So far, we have obtained a maximum mobility of 600 cm²/V-s in a 6 μm GaN epilayer. Atomic force microscopy (AFM) analysis of the buffer layer and x-ray analysis of the main epilayer lead us to conclude that the both of these effects reflect the degree of coherence in the main GaN epitaxial layer. These results are consistent with the growth model presented by Hiramatsu et al., however, our AFM data indicates that for GaN buffer layers partial coherence can be achieved during the low temperature growth stage.     

基于不同金属衬底制备碳膜的场发射研究

利用磁控溅射的方法,在相同的陶瓷衬底上面分别镀上三种不同金属,形成三种不同的金属衬底,对金属层进行相同的表面处理后,放入微波等离子体化学气相沉积腔中,制备出三种碳膜。对制备出不同的碳膜用扫描电镜、拉曼光谱、X射线衍射仪进行结构分析,并用二极管型结构测试了它们的场致发射电子的性能。找到了最适合场发射的金属衬底,进一步对不同金属衬底制备碳膜的场发射特性不同的原因进行了初步的研究。     

球状微米金刚石的制备过程及其场发射性能的研究

在纯平的陶瓷衬底上面,利用磁控溅射方法镀上一层金属钛。对金属钛层进行表面缺陷处理后,放入微波等离子体化学气相沉积腔中,利用正交实验方法制备出场发射性能最优的薄膜,通过扫描电镜、X射线衍射仪、拉曼光谱仪等仪器,研究了薄膜的微观表面形态、结构组成等,得到了该薄膜是球状微米金刚石薄膜的结论。并进一步研究了最优场发射薄膜的发射机理。