Table of Content

15 May 2022, Volume 51 Issue 5

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Thirty Years of Chemical Vapor Deposition (CVD) Diamond Films Research in China

LYU Fanxiu, LI Chengming

2022, 51(5):  753-758. 

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Since the advent of the chemical vapor deposition (CVD) diamond film 1980s, Chinese researchers quickly follow up in a short time from the national level layout. In the era when China's science and technology need to catch up, the implementation of the “863 Program” has strongly promoted the progress of the CVD diamond film technology in China from 1987 to 2016. Until now, the national key research and development program is still supporting the application research of CVD diamond in various fields. The review of the development of CVD diamond film in the past 30 years has important reference significance for the design of science and technology strategy, the formulation of science and technology policy, the implementation of scientific research plan and the implementation of scientific and technological achievements in China.

Reviews

Progress of Chemical Vapor Deposition (CVD) Diamond

LI Chengming, REN Feitong, SHAO Siwu, MU Lianxi, ZHANG Qinrui, HE Jian, ZHENG Yuting, LIU Jinlong, WEI Junjun, CHEN Liangxian, LYU Fanxiu

2022, 51(5):  759-780. 

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Chemical vapor deposition (CVD) technology has enabled synthetic diamonds to be applied in many fields, in which the excellent comprehensiveness of diamond has been fully developed, and may lead to a leap-forward development. The color center makes the diamond quantum accelerator initially show the feasibility of great power. Various scenarios, including the application of UV laser writing technology windows, maximize the comprehensive advantages of diamond windows in terms of optics, electricity, heat and mechanics. Ultra-wide bandgap diamond semiconductor applications will soon be realized, and diamond heat dissipation applications are constantly expanding. By summarizing the preparation methods and characteristics of CVD diamond, according to the intrinsic characteristics of diamond, CVD diamond is classified into quantum grade, electronic grade, optical grade, thermal grade and mechanical grade. The current status of research and application of CVD diamond are reviewed in detail, which is of great significance for judging the future development trend of CVD diamond.

Research Progress of Cubic Boron Nitride

LIU Caiyun, GAO Wei, YIN Hong

2022, 51(5):  781-800. 

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As the Ⅲ-Ⅴ binary compound with the face-centered cubic structure of sphalerite, cubic boron nitride (c-BN) exhibits the largest band gap as one of the typical third-generation semiconductors, as well as other excellent properties including high thermal conductivity, high hardness, high-temperature oxidation resistance, chemical stability, wide range of light transmission wavelength, and can be both doped into p-type or n-type. It can be not only widely used as a superhard materials in the processing fields of various industries, but also has potential applications value as extreme electronics materials in high-power semiconductor and optoelectronic devices, making it suitable for extreme environments such as high temperature, high power, high pressure, high frequency and strong radiation. This article reviews the development of c-BN crystal preparation and epitaxial growth of c-BN thin films in recent years, focusing on the progress of growth technology and the improvement of crystal quality, as well as their mechanical, optical and electrical properties. Finally, the paper summarizes the content of the paper and prospects the challenges of c-BN application.

Research Progress on Diamond Radio-Voltaic Effect Isotope Batteries Devices

LIU Benjian, ZHANG Sen, HAO Xiaobin, WEN Dongyue, ZHAO Jiwen, WANG Weihua, LIU Kang, CAO Wenxin, DAI Bing, YANG Lei, HAN Jiecai, ZHU Jiaqi

2022, 51(5):  801-813. 

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MEMS, deep space and deep sea exploration tasks put forward higher requirements for long-term and portable power supply. Due to its high energy density and stable power output, isotopic battery can continuously provide energy for Lunar Rover and seabed detector in extreme environments such as high and low temperature and no sunlight. As the main type of isotope battery, radio-voltaic effect isotope battery has been widely studied because of its high theoretical energy conversion efficiency and easy miniaturization, and it has been successfully applied to cardiac pacemaker. The isotope battery made of energy converters using semiconductor with wide band gap can obtain higher energy conversion efficiency. The 5.5 eV band gap and radiation resistance of single crystal diamond make it the best choice for making energy converters for radio-voltaic effect isotope batteries. With the development of chemical vapor deposition technology, the epitaxial technology of diamond crystal has made rapid progress, which has laid a material foundation for the development of diamond semiconductor devices. The characteristics of common semiconductor materials for energy converters and radiation source materials for isotopic battery are compared in this paper, the basic principle of radio-voltaic effect is introduced, then the key parameters of radio-voltaic effect isotopic battery is analyzed, and the literatures on the research of diamond radio-voltaic effect isotopic battery are summarized. The development status and existing problems of diamond isotope battery are pointed out. By analyzing the current performance and application of hetero pn junction composed of diamond and other n-type semiconductor materials, the structural design of high-performance isotope battery based on diamond hetero pn junction is given, summarized and prospected.

Research Progress of Nuclear Radiation Detectors with CVD Synthetic Diamond

MU Lianxi, ZENG Hansen, ZHU Xiaohua, TU Juping, LIU Jinlong, CHEN Liangxian, WEI Junjun, LI Chengming, OUYANG Xiaoping

2022, 51(5):  814-829. 

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Owing to their small volume, strong radiation resistance and fast time response, diamond detectors show the obvious advantage of application in nuclear radiation area. At early stage, diamond nuclear radiation detectors were made of natural diamond materials. With the development of chemical vapor deposition (CVD) diamond synthetic technology, the development and application of diamond radiation detector has been greatly promoted. In this paper, starting with the CVD synthetic diamond material, the impurities and defects that restrict the performance of diamond detectors, the synthetic process of CVD diamond, the characterization method of impurities and defects in detector grade diamond are analyzed systematically. Based on the performance indicators such as the product of carrier mobility and life, the charge collection efficiency of detector, etc., the effects of impurities and defects in CVD diamond on the performance of the detector are summarized. The application status of diamond nuclear radiation detectors abroad is introduced and the development prospect of domestic diamond nuclear radiation detectors is also viewed.

HPHT Synthesis of Boron Co-Doped Single Crystal Diamond

WANG Zhiwen, MA Hongan, CHEN Liangchao, CAI Zhenghao, JIA Xiaopeng

2022, 51(5):  830-840. 

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Diamond is a superhard and multi-functional material with excellent properties. Synthetic diamond can own unique properties by doping. Boron-doped diamond has both conductive characteristics of p-type semiconductor and excellent physical and chemical properties. It has wide application value in national defense, medical treatment, exploration, scientific research and other fields. Based on boron-doped diamond and boron co-doped diamond single crystals synthesized by high pressure and high temperature (HPHT) method in our laboratory, the synthesis and properties of boron-doped diamond, boron-hydrogen co-doped diamond and boron-nitrogen co-doped diamond are discussed. The influence of different additives on the synthesis properties of the synthetic diamonds through the optical and electrical characterization are analyzed, which provides some ideas for further synthesizing high-performance semiconductor diamonds.

p-Type and n-Type Doping of Single Crystal Diamond

NIU Keyan, ZHANG Xuan, CUI Boyao, MA Yongjian, TANG Wenbo, WEI Zhipeng, ZHANG Baoshun

2022, 51(5):  841-851. 

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Diamond as an ultra-wide band gap semiconductor material shows excellent properties in thermal conductivity, carrier mobility and breakdown field strength, and has broad application prospects in the field of power electronics. The realization of p-type and n-type conduction is essential to fabricate diamond electronic devices. Between them, the development of p-type diamond is relatively mature, and boron is the mainstream doping element. However, the hole mobility decreases rapidly at a high doping concentration. The main doping element of n-type diamond is phosphorus. At present, there are still challenges such as deep impurity level, large ionization energy, and defects in diamond crystals after doping, resulting in low carrier concentration and mobility, and the resistivity is difficult to meet the requirements of devices. Therefore, the realization of high quality p-type and n-type diamond has become the focus of researchers. This paper mainly introduces the unique physical properties of single crystal diamond, outlines the basic principles and key parameters of the chemical vapor deposition method and ion implantation method of doping, then reviews the research progress on the p-type and n-type doping of single crystal diamond films by the two methods, systematically summarizes the facing problems and the prospects of future development.

Research Progress on the Effects of Surface Functionalization of Nanodiamonds

ZHAO Ziwei, GAO Xiaowu, CAO Wenxin, LIU Kang, DAI Bing, WANG Yongjie, ZHU Jiaqi

2022, 51(5):  852-864. 

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Nanodiamonds have shown excellent mechanical properties, thermal conductivity, biocompatibility and structural tunability, and have been widely demonstrated their application in the fields of composite materials, electrochemistry, catalysis, medicine and so on. In industry, the mass production of nanodiamonds by detonation method provides a foundation for their application. Due to the complex surface structure of nanodiamonds, precise control is required to achieve the target performance and the research on surface functionalization is of great practical significance. This review firstly introduces various surface modification methods of nanodiamonds, then focuses on the impact of surface functionalization research on the application of nanodiamonds in mechanical properties, catalytic properties and biomedical fields, and finally prospects the future research direction of nanodiamonds.

Doping, Surface/Interface Regulation and Properties of Nanocrystalline Diamond Films

HU Xiaojun, ZHENG Yuhao, CHEN Chengke, LU Shaohua, JIANG Meiyan, LI Xiao

2022, 51(5):  865-874. 

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In this paper, doping, electric conductivity, field emission and electrochemical properties of nanocrystalline diamond films are reviewed, which contain n-type nanocrystalline diamond (NCD) films prepared by chemical vapor deposition, improvement of n-type electrical conductivity in NCD films by ion implantation, excellent field emission properties of NCD films prepared by metal ion implantation, high mobility n-type conductivity obtained by low dose ion implantation and oxygen termination on grain surface, regulation of the structure of NCD/graphene and its influence on electrical and electrochemical properties, microstructure and electrochemical regulation of boron-doped NCD film electrodes and so on. It shows through comprehensive analysis that grain doping and surface/interface coordination can improve the electrical properties, field emission properties and electrochemical properties of thin films, which has important application prospects in the fields of diamond-based nano-electronic devices and electrochemical electrodes.

Retention of New Functional Carbon Materials under High Pressure

LYU Chaofan, ZANG Jinhao, YANG Xigui, SHAN Chongxin

2022, 51(5):  875-880. 

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Functional materials with highly desirable properties have been highly pursued for a long time due to their potential applications in many fields. High pressure can effectively reduce the interatomic distances and modulate the bonding patterns of materials without changing their chemical compositons, which has been considered as a powerful and important approach to design new functional materials with desired structures and properties. Many interesting types of functional carbon materials, such as optical transparent carbon, super strong and elastic carbon, and ultrahard bulk amorphous carbon have been obtained from different carbon precuresors under high pressure. Recent progress on the high pressure research of low dimensonal carbon composite materials are introduced. Based on the predesigned carbon-based precursors, new carbon materials with superhard properties, covalent polymerization and anomalous photoluminescence enhancement by the application of high pressure have been obtained.

Transition Metal Light Elements Compounds Synthesized by High Pressure and High Temperature

YOU Cun, ZHAO Wei, WANG Xin, DONG Shushan, TAO Qiang, ZHU Pinwen

2022, 51(5):  881-892. 

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Transition metal light elements compounds (TMLEs) are a kind of robust functional materials due to high hardness, high melting point, superior conductivity, magnetic properties, and superconductivity. The combination of excellent mechanical properties and functionality makes TMLEs special materials used in extreme environments. However, synthesizing TMLEs need high pressure and high temperature (HPHT) conditions to overcome the energy barrier. Although many TMLEs were synthesized by HPHT, the growth mechanism is still mysterious. Summary of TMLEs synthesized by HPHT is significant to understand the growth process and develop of new TMLEs. In this work, the TMLEs synthesized by HPHT which include our groups research experience and other relevant literatures are summarized. The TMLEs include transition metal borides (TMBs), transition metal carbides (TMCs), and transition metal nitrides (TMNs). The starting materials, experimental conditions, and morphologies etc. are analyzed. The main results are as follows: proportion of starting materials and the suitable temperature are very important to obtain the single phase of TMBs; the boron subunit in TMBs is related to growth kinetics, which induces step growth process; choosing different starting materials of carbon and nitrogen will define the growth process of TMLEs. Synthesizing single crystal with millimeter size in the future is meaningful to understand the basic properties of TMLEs. The new structures of TMLEs with high content of light elements still need to be developed. With the development of new materials, TMLEs will be a kind of irreplaceable robust materials in the future.

Research Articles

Homoepitaxial Boron Doped Single Crystal Diamond and Its Electrical Properties

WANG Ruozheng, YAN Xiuliang, PENG Bo, LIN Fang, WEI Qiang, WANG Hongxing

2022, 51(5):  893-900. 

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The breakthrough of high quality and high efficiency diamond doping is the premise of realizing high-performance diamond power electronic devices. In this paper, the homoepitaxial growth of high-quality boron doped single crystal diamond was prepared by MPCVD with trimethylboron as the source gas. The surface roughness is 0.35 nm, the full width at half maximum (FWHM) of XRD (004) rocking curves is 28.4 arcsec, and the FWHM of Raman spectrum is 3.05 cm^-1. By changing the boron concentration in the gas component, the controlled p-type diamond doping with the concentration from 10¹⁶ cm^-3 to 10²⁰ cm^-3 was realized. Then, the effects of deposition conditions such as B/C ratio, growth temperature and methane content on the electrical properties of p-type diamond were studied. The hole mobility of 207 cm²/(V·s) has been obtained with the B/C ratio of 20×10^-6, the growth temperature of 1 100 ℃, the CH₄/H₂ ratio of 8% and the chamber pressure of 160 mbar. Furthermore, the crystal quality of boron doped diamond can be improved with the adding of oxygen in the gas component, that is to say, reducing the impurity scattering. When the O₂/H₂ ratio is 0.8%, the hole mobility increases significantly to 614 cm²/(V·s).

Preparation and Surface Optimization of Synthetic Diamond Single Crystal Film

YIN Zimeng, ZHENG Kaiwen, ZOU Xingjie, LU Xinyu, CHEN Kai, YE Yucong, HU Wenxiao, TAO Tao

2022, 51(5):  901-909. 

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Single crystal diamond film has been developed as high efficiency thermal management substrate, which has a promising potential in the field of wide bandgap semiconductor electronic devices. However, the slow production yield and rough surface of diamond film grown by microwave plasma chemical vapor deposition (MPCVD) make it unavailable as the substrate for semiconductor devices. In this work, single crystal diamond films were grown by MPCVD step by step, of which the growth rate was compared and the surface morphology and crystal quality was estimated by photos, XRD, AFM and Raman measurements. High-speed single crystal epitaxial diamond layer which could reach 20 μm/h with smooth surface was acquired by two-step growth technique of adjusting methane concentration. It is beneficial to solve the problems of rough surface morphology and processing difficulties of diamond epitaxial films in the subsequent fabrication of related electronic devices, so as to support the development of high power electronic devices.

Microwave Power and Deposition Pressure Matching of MPCVD Diamond Films

ZHANG Shuai, AN Kang, SHAO Siwu, HUANG Yabo, YANG Zhiliang, CHEN Liangxian, WEI Junjun, LIU Jinlong, ZHENG Yuting, LI Chengming

2022, 51(5):  910-919. 

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High-quality diamond prepared by microwave plasma chemical vapor deposition (MPCVD) has application prospects in many high-precision fields. The film deposition experiments were carried out using microwave power 9 kW. The chamber pressures are 13 kPa, 14 kPa, 15.5 kPa, and 17 kPa, respectively. It was found that the deposited films under pressure of 15.5 kPa and 17 kPa exhibit abnormal growth in the central region, which is manifested as an obvious stepped bulge in the center. Surface morphology and film quality of the film were analyzed by SEM and Raman in order to reveal the reason for the abnormal deposition in the center of the film. Meanwhile, the deposition process was modeled, the power density and flow field distribution were calculated and analyzed by numerical simulation. The results show that at the same power, increasing the chamber pressure and compressing the plasma will lead to more dense growth in the central region of the film than that in the edge region and obvious steps in the central region of the diamond film, due to the short mean free path and insufficient diffusion capacity. The overall growth rate, uniformity and quality of the film will decrease after exceeding pressure limit.

Structure, Optical Properties and Thermal Stability of Nanodiamond

CHENG Xuerui, HUANGFU Zhanbiao, CAI Yule, WU Xiwang, YANG Kun

2022, 51(5):  920-925. 

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Nanodiamond combines the properties of both nanomaterials and diamond materials, resulting in different characteristics from that of micron and bulk diamond. In this work, the structure, optical properties and thermal stability of diamond samples with different sizes were studied by scanning electron microscopy, X-ray diffraction, spectroscopy techniques and thermogravimetric analysis. The results show that the sizes of three samples are 300 μm, 30 μm and 100 nm, respectively. Diamond samples with larger size present better crystal quality, and are confirmed to be Ⅰb type diamond because single nitrogen impurities are observed. In contrast, the crystallinity of nanodiamond samples is poor, and residual graphite is detected in nanodiamond samples from both XRD and Raman results. In addition, H₂O, N—H and C—H bonds are observed in nanodiamond, suggesting there may be many organic reactive groups on surface. Two emission peaks are observed in both samples of 300 μm and 30 μm, originated from two types of nitrogen vacancy defects with neutral and negative charge respectively. In contrast, no emission is observed for nanodiamond because of fluorescence quenching from nonradiative center originated from organic groups and surface defects in the nanodiamond. Diamond samples with large size have the intensive absorption in the range from 300 nm to 525 nm, while the nanodiamond sample show strong absorption in the entire UV-visible-NIR region resulting in much lower transmittance. With the decrease of particle size, both the initial oxidizing temperature and oxidizing rate gradually decline. As a result, larger size samples have better thermal stability.

Spectroscopy Characterization Study on Quality and Defects of Pure Diamond

ZHANG Yufei, WANG Kaiyu, LI Junlin, QIN Zhenxing, TIAN Yuming

2022, 51(5):  926-932. 

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In this paper, the low-temperature Raman and photoluminescence (PL) spectroscopy were employed to study the crystallization degree, stress distribution of the pure diamond film. Combined with electron irradiation and rapid annealing, the impurity defect structure of the pure diamond film was studied. Raman spectroscopy analysis shows that the stress distributions in edge and surface of the film are higher than in interior, which may be ascribed to the diamond growth mechanism, physical cutting and polishing damage to the films. The zero phonon lines in PL spectra show obvious temperature dependent, and the spectra peaks redshift, intensity reduction and low-temperature splitting with increase of temperature were explained by Jahn-Teller effect and electron-phonon coupling theory. Low temperature PL spectra observed distinct NV defects in the film after electron irradiation and 700 ℃ annealing,which indicate that the nitrogen mainly existed in the lattice with a form of substitution impurities.

Effect of Ti, V, Ni and Mo on Nucleation of CVD Diamond Coating

JIAN Xiaogang, PENG Xinying, YANG Tian, HU Jibo, YIN Mingrui

2022, 51(5):  933-940. 

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To better understand the influence mechanism of transition metal elements (Ti, V, Ni, Mo) on the nucleation of chemical vapor deposition (CVD) diamond coating, the intrinsic mechanism of the CH₃ adsorption on impregnated diamond cemented carbides through geometry, interaction energy, Mulliken charge distribution, visualization of the interactions, charge density difference and density of state (DOS) were investigated theoretically. All the calculations were performed by density functional theory. The calculated results indicate that diamond surface doped with Ti/V/Ni/Mo, rather than pure diamond surface, exhibits stronger interactions. The adsorption capacity is related to the valence electron structure of each atom, and the surface doped with Ti has the most stable adsorption capacity. The charge transfer between CH₃ and Ni is more easier to form covalent bond, Mo is beneficial to promote the dehydrogenation reaction of CH₃. Ti, V, Ni and Mo are conducive to increasing the nucleation density and improving the strength of CVD diamond coating.

Integrated Processing of Grinding and Polishing for Large-Size Single Crystal Diamond

WEN Hailang, LU jing, LI Chen, HU Guangqiu

2022, 51(5):  941-947. 

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Due to its excellent physical properties, diamond is regarded as a next-generation semiconductor material. However, its extremely high hardness, brittleness, and corrosion resistance cause the diamond difficult to process, especially for large-size chemical vapor deposition (CVD) single crystal diamonds (SCD). Currently, researchers have not explored an efficient and low-cost method for ultra-precision processing diamond wafers. Based on the rotary infeed surface grinding, integrated processing technology of grinding and polishing by the concentric double grinding wheel was proposed in this paper. In one clamping, the SCD surface is flattened by the inner ring ceramic grinding wheel that the abrasive is diamond, and then the surface after grinding is polished by sol-gel (SG) polishing wheel that the abrasives are diamond mixed with CuO. In the processing of grinding and polishing integration, the surface roughness of SCD can be reduced from about 46 nm to less than 0.3 nm in a short time. In the grinding, the ceramic grinding wheel with diamond abrasive scratches the SCD surface at high speed. The strong mechanical action causes the large material removal, obtains nano-level smooth surface of SCD, and causes the surface amorphization. In the SG polishing, the diamond abrasive scratches the SCD surface at high speed to form a high-temperature and high-pressure environment, which further induces the oxidation-reduction reaction between the CuO powder and the amorphous carbon for realizing reactive polishing. The integrated processing technology of grinding and polishing provides a reference for the industrial production of SCD wafers and polycrystalline diamond (PCD) wafers in the future.