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  • Coessential-connection by microwave plasma chemical vapor deposition: a common process towards wafer scale single crystal diamond

    Guoyang Shu,
    Bing Dai,
    Andrey Bolshakov,
    Weihua Wang,
    Yang Wang,
    Kang Liu,
    Jiwen Zhao,
    Jiecai Han,
    Jiaqi Zhu

    Large size single crystal diamond (SCD) wafer has been strongly desired for various of advanced applications, while two major potential approaches, including mosaic growth and heteroepitaxy based on chemical vapor deposition method, are both stuck with respective technical barriers. This paper reveals and summarizes the essential commonality of the two schemes, and denominates the concept of “coessential-connection” (CC) growth. Such generalized concept involved the nature of the single crystal and polycrystalline diamond film deposition with similar mechanism and processes. The principle of CC growth process with detailed classification was elaborated, and influence of nucleus size and orientation mismatch was clarified, which is regarded as the core problem of large area SCD film growth via coessential-connection process.

    Single crystal diamond;
    crystal growth;
    Functional Diamond
    Volume 1, Issue 1 (2021)
  • Hydrogen-terminated diamond MOSFETs on (0 0 1) single crystal diamond with state of the art high RF power density

    Cui Yu,
    Chuangjie Zhou,
    Jianchao Guo,
    Zezhao He,
    Mengyu Ma,
    Hao Yu,
    Xubo Song,
    Aimin Bu,
    Zhihong Feng

    Diamond field-effect transistor (FET) has great application potential for high frequency and high power electronic devices. In this work, diamond FETs were fabricated on (0 0 1) single crystal diamond with homoepitaxial layer. The nitrogen impurity content in the homoepitaxial layer is greatly decreased as measured by the Raman and photoluminescence spectra. The diamond field effect transistor with 100 nm Al2O3 as gate dielectric shows ohomic contact resistance of 35 Ω . mm, maximum drain saturation current density of 500 mA/mm, and maximum transconductance of 20.1 mS/mm. Due to the high quality of Al2O3 gate dielectric and single crystal diamond substrate, the drain work voltage of −58 V is achieved for the diamond FETs. A continuous wave output power density of 4.2 W/mm at 2 GHz is obtained. The output power densities at 4 and 10 GHz are also improved and achieve 3.1 and 1.7 W/mm, respectively. This work shows the application potential of single crystal diamond for high frequency and high power electronic devices.

    field effect transistor;
    power density
    Functional Diamond
    Volume 2, Issue 1 (2022)
  • Diamond dislocations analysis by X-ray topography

    Shinichi Shikata

    The dislocation identification method using X-ray topography by reflection mode geometry was applied to characterize IIa, Ib and highly B doped high pressure high temperature (HPHT) grown crystals. In both IIa and Ib crystals, dislocations are found to propagate in the <111> grown direction, with dominant vectors of [110] and [1-10], neither of which has no c-axis segment. For Ib crystal, many dislocations are also generated in the <112> and <121> directions, which are slightly tilted to <111>. It was confirmed that the dislocations in the same direction have the same Burgers vectors, but the dislocations are spread in broad area. A total of up to 20 HPHT crystals were measured and found to exhibit different dislocation distributions. This indicates an immature growth technique in terms of dislocation. Measurements of four chemical vapor deposition (CVD) substrates showed numerous dislocation bundles, making individual dislocation directions analysis impossible. CVD substrates suffer from an increase in dislocations due to CVD growth, resulting in poor diamond quality in terms of dislocation. XRT analysis on dislocations of epitaxial growth will be very important prior to CVD substrates analysis.

    power device;
    X-ray topography
    Functional Diamond
    Volume 2, Issue 1 (2022)
  • Room-temperature bonding of GaN and diamond via a SiC layer

    Ayaka Kobayashi,Hazuki Tomiyama,Yutaka Ohno,Yasuo Shimizu,Yasuyoshi Nagai,Naoteru Shigekawa,Jianbo Liang

    A GaN-on-diamond structure is the most promising candidate for improving the heat dissipation efficiency of GaN-based power devices. Room-temperature bonding of GaN and diamond is an efficient technique for fabricating this structure. However, it is extremely difficult to polish diamond to an average roughness (Ra) below 0.4 nm, especially for polycrystalline diamond. In this work, Room-temperature bonding of GaN and rough-surfaced diamond with a SiC layer was successfully achieved by a surface-activated bonding (SAB) method. The diamond surface’s initial Ra value was 0.768 nm, but after deposition of the SiC layer, the Ra decreased to 0.365 nm. The SiC layer formed at the as-bonded GaN/diamond interface was amorphous, with a thickness of about 7 nm. After annealing at 1000-°C, the amorphous SiC layer became polycrystalline, and its thickness increased to approximately 12 nm. These results indicate that the deposition of a SiC layer on diamond can efficiently lower the diamond surface’s roughness and thus facilitate room-temperature bonding.

    GaN/diamond interface;
    SiC layer;
    heat dissipation;
    thermal management;
    surface-activated bonding
    Functional Diamond
    Volume 2, Issue 1 (2022)
  • Progress in semiconductor diamond photodetectors and MEMS sensors

    Meiyong Liao

    Diamond with an ultra-wide bandgap shows intrinsic performance that is extraordinarily superior to those of the currently available wide-bandgap semiconductors for deep-ultraviolet (DUV) photoelectronics and microelectromechanical systems (MEMS). The wide-bandgap energy of diamond offers the intrinsic advantage for solar-blind detection of DUV light. The recent progress in high-quality single-crystal diamond growth, doping, and devices design have led to the development of solar-blind DUV detectors satisfying the requirement of high Sensitivity, high Signal-to-Noise ratio, high spectral Selectivity, high Speed, and high Stability. On the other hand, the outstanding mechanical hardness, chemical inertness, and intrinsic low mechanical loss of diamond enable the development of MEMS sensors with boosted sensitivity and robustness. The micromachining technologies for diamond developed in these years have opened the avenue for the fabrication of high-quality single-crystal diamond mechanical resonators. In this review, we report on the recent progress in diamond DUV detectors and MEMS sensors, which includes the device principles, design, fabrication, micromachining of diamond, and devices physics. The potential applications of these sensors and a perspective are also described.

    Single-crystal diamond;
    Functional Diamond
    Volume 1, Issue 1 (2021)
  • Orientated growth the 3D diamond/graphene hybrid arrays and the application in thermal interface materials

    Guorong Zhang,
    Huiqiang Liu,
    Yangxin Xiao,
    Bing Wang,
    Jian Wang,
    Wen Zhang,
    Ying Xiong
    Diamond and graphene are considered to be one of the most promising thermal interface materials (TIMs) for electronic devices benefited from their highest thermal conductivity in the natural world. However, orientated fabrication of high thermal conductivity diamond and graphene hybrid arrays with three dimensions (3 D) thermal conductive networks are still problematic. Here, we used a unique one-step microwave plasma chemical vapor deposition, n-butylamine, as the liquid source to prepare a novel high thermal conductivity 3 D vertical diamond/graphene (VDG) hybrid arrays films. The orientated 3 D thermal conduction path of the VDG is regulated by the growth temperature, and the through-plane thermal conductivity value of the VDG700 films up to 97 W m−1 K−1. In the actual TIM performance measurement, the system cooling efficiency with our VDG as TIM is higher than the state-of-the-art commercial TIM, demonstrating the superior ability to solve the inter-facial heat transfer issues in electronic systems.
    liquid source;
    hybrid films;
    heat dissipation
    Functional Diamond
    Volume 2, Issue 1 (2022)
  • Past, present, and the future of the research and commercialization of CVD diamond in China

    F. X. Lu

    It has been half of a century since the publication of the early reports about CVD diamond films in the world in the early 1970’s. The reports for meaningful laboratory growth of diamond films with much higher growth rate and higher quality could be found in the early 1980’s, under the so-called “Diamond Fever” initiated all over the world. In less than 10 years later, CVD diamond research had started in China as “863 Plan” (High Technology Research and Development Plan in China), a newly launched program in 1987. 35 years later, it is very interesting to explore what really happened to the CVD diamond in China. As a multi-functional material with a vast combination of extraordinary electrical, mechanical, thermal, optical, acoustic, and electro-chemistry properties, the CVD diamond has wide applications potentially in the field of multidiscipline high technologies. Therefore, this article aims to provide a general review on the CVD diamond by presenting a clearer picture about the history, the research status and its development, particularly the commercialization in China. Finally, the general trend in the near future is discussed.

    CVD diamond;
    research and development;
    Functional Diamond
    Volume 2, Issue 1 (2022)
  • Research progress of spectra and properties of ultrahard carbon materials at high pressure and high temperature

    Zhiqiang Hou,
    Haikuo Wang,
    Yao Tang,
    Jiakun Wu,
    Chao Wang,
    Zhicai Zhang,
    Xiaoping Ouyang
    Carbon, the fourth most abundant element in the Universe, possesses numerous allotropes with diverse bonding character (sp1-, sp2- and sp3-hybridized bonds) and structural motif of the constituting atoms. In particular, the carbon materials with a fully or nearly 100% sp3-hybridized strong C-C bonds often lead to excellent mechanical properties, chemical stability, thermal and optical properties, such as crystalline diamond and diamond-like amorphous carbon (DLC). In this review, we systematically summarize the synthesis, microstructure, mechanical properties, thermal and optical properties of ultrahard carbon materials with current experimental results on nano-polycrystalline diamond (NPD), nanotwinned diamond (NTD), micro-grained polycrystalline diamond (MPD), and amorphous diamond/carbon. In addition, we discuss the difference of spectra of XRD, Raman and EELS between various nanocrystalline diamond powder and ultrahard carbon materials. Finally, we provide our insights into the future development and applications in the research of ultrahard carbon bulk materials by high-pressure and high-temperature techniques according to the current advantages, limitations and challenges in the experiment.
    high pressure and high temperature (HPHT)
    Functional Diamond
    Volume 2, Issue 1 (2022)
  • Science and technology of a transformational multifunctional ultrananocrystalline diamond (UNCD) coating

    Orlando Auciello

    This review focuses on describing the fundamental/applied materials science and technological applications of a transformational multifunctional diamond-based material named ultranano­crytalline diamond (UNCDTM) in film form. The UNCDTM films are synthesized using microwave plasma chemical vapor deposition (MPCVD) and hot filament chemical vapor deposition (HFCVD), via patented Ar/CH4 gas flown into air evacuated chambers, using microwave power, or hot filaments’ surface, to crack CH4 molecules to generate C atoms and CHx (x = 1, 2, 3) species, which produce chemical reactions on substrates’ surfaces, producing diamond film with grain sizes in the range 3–5 nm (smallest grain size known today for any polycrystalline diamond film), providing the bases for the name UNCD. UNCD coatings exhibit a unique combination of properties, namely: (1) super high hardness and Young modulus, similar to the crystal gem of diamond; (2) lowest coefficient of friction compared to other diamond or diamond-like coatings; (3) no mechanical surface wear; (4) highest resistance to chemical attach by any corrosive fluid; (5) only diamond film exhibiting electrical conductivity via Nitrogen inserted in grain boundaries, binding to C atoms and providing electrons for electrical conduction, or B atoms substituting C atoms in the diamond lattice, providing electrons to the conduction band; and (6) best biocompatibility, since UNCD coatings are formed by C atoms (element of life in human DNA, cells/molecules). The UNCD films’ properties provide unique multifunctionalities, enabling new generations of industrial, electronic, high-tech, and implantable medical devices/prostheses, enabling substantial improvement in the way and quality of life of people worldwide.

    Functional Diamond
    Volume 2, Issue 1 (2022)
  • Heteroepitaxy of diamond semiconductor on iridium: a review

    Weihua Wang,Benjian Liu,Leining Zhang,Jiecai Han,Kang Liu,Bing Dai,Jiaqi Zhu

    As one of the representatives of carbon-based semiconductors, diamond is called the “Mount Everest” of electronic materials. To maximize its properties and realize its industrial applications, the fabrication of wafer-scale high-quality diamonds is critical. To date, heteroepitaxy is considered as a promising method for the growth of diamond wafers with considerable development. In this review, fundamentals of diamond heteroepitaxy is firstly introduced from several perspectives including nucleation thermodynamics and kinetic, nucleation process at the atomic level, as well as the interplay between the epitaxial film and substrate. Second, the bias enhanced nucleation (BEN) method is reviewed, including BEN setup, BEN process window, nucleation phenomenology (mainly on Iridium), nucleation mechanism by ion bombardment, and large-scale nucleation realization. Third, the following textured growth process is presented, as well as grain boundary annihilation, and dislocation and stress reduction technologies. Fourth, the applications of diamonds in electronic devices are studied, showing its excellent performances in the future power and electronic devices. Finally, prospects in this field are proposed from several aspects.

    Diamond wafer;
    large size;
    bias enhanced nucleation;
    textured growth;
    electronic applications
    Functional Diamond
    Volume 2, Issue 1 (2022)