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This paper reviews recent progress in diamond radiation detectors. Diamond is an ultra-wide gap (5.5 eV) semiconducting material which has several ideal properties for radiation detectors, such as solar blindness, high temperature operation, and fast response. Furthermore, diamond has near tissue-equivalence due to its low atomic number (Z = 6) and chemical stability due to its strong covalent bonds. Because of these features, diamond has long been used as a radiation detector in the fields of nuclear engineering, nuclear fusion, high energy physics and medical therapy. Until the 1990s, most of the research was conducted using selected high purity natural diamonds. Since the 2000s, the detector characteristics of synthetic diamond detectors have been greatly improved by achieving high purity diamond by microwave plasma enhanced chemical vapor deposition (CVD). Single-crystal CVD diamonds present best characteristics for spectroscopy in diamond radiation detectors. For applications requiring large sensitive areas, polycrystalline CVD diamond is mostly used. Heteroepitaxial diamond detectors are a promising alternative to increase the area of spectroscopic diamond radiation detectors. For applications in extreme environments, high radiation flux which leads to polarization effects is a crucial issue. Even with diamond, which has excellent radiation hardness, degradation of detector characteristics due to irradiation is inevitable. Detectors designed with small carrier travel distances, such as membrane diamond detectors and three-dimensional diamond radiation detectors, are effective ways to mitigate the degradation.

The burgeoning multi-field applications of diamond concurrently bring up a foremost consideration associated with nitrogen. Ubiquitous nitrogen in both natural and artificial diamond in most cases as disruptive impurity is undesirable for diamond material properties, eg deterioration in electrical performance. However, the feat of this most common element-nitrogen, can change diamond growth evolution, endow diamond fancy colors and even give quantum technology a solid boost. This perspective reviews the understanding and progress of nitrogen in diamond including natural occurring gemstones and their synthetic counterparts formed by high temperature high pressure (HPHT) and chemical vapor deposition (CVD) methods. The review paper covers a variety of topics ranging from the basis of physical state of nitrogen and its related defects as well as the resulting effects in diamond (including nitrogen termination on diamond surface), to precise control of nitrogen incorporation associated with selective post-treatments and finally to the practical utilization. Among the multitudinous potential nitrogen related centers, the nitrogen-vacancy (NV) defects in diamond have attracted particular interest and are still ceaselessly drawing extensive attentions for quantum frontiers advance.

AbstractThe mainstream polishing methods were reviewed in light of polycrystalline CVD diamond wafer with large area. The principles, equipment, and processes of the mainstream polishing methods were reviewed, and the processing characteristics of these methods were compared. The material removal rate (MRR), polishing rate (PR), and minimum surface roughness (Ra) obtained by each polishing method were summed up. The non-contact method has a relatively higher MRR than the contact method, while the contact method has a relatively smaller final roughness than the non-contact method. Two factors, K (K = ΔRa/Δm, ΔRa is the reduction of the surface roughness, Δm is the mass loss) and CI (CI = K/t, t is the total polishing time), were proposed to evaluate the influence of the polishing parameters on the polishing course in the contact polishing methods and to describe the feature of each polishing method, respectively. The variation of the K value indicated that the polishing load and the polishing plate speed did not always influence the polishing effect monotonically in every contact polishing method, and it should be optimized to obtain fine surface roughness with the tiny mass loss. The CI value showed that the non-contact polishing method possessed the feature of high roughness improvement with low mass loss in the unit polishing time. These results reveal how to move forward on the path to polishing large area polycrystalline CVD diamond wafer.

With the increasing power density and reduced size of the GaN-based electronic power converters, the heat dissipation in the devices becomes the key issue toward the real applications. Diamond, with the highest thermal conductivity among all the natural materials, is of the interest for integration with GaN to dissipate the generated heat from the channel of the AlGaN/GaN high electron mobility transistors (HEMTs). Current techniques involve three strategies to fabricate the GaN-on-diamond wafers: bonding of GaN with diamond, epitaxial growth of diamond on GaN, and epitaxial growth of GaN on diamond. As a result of the large lattice mismatch and thermal mismatch, the integration of GaN-on-diamond wafer is suffered from stress, bow, crack, rough interfaces, and large thermal boundary resistance. The interfaces with transition or buffer layers impede the heat flow from the device channel and greatly influence the device performance. In this review, we summarize the three different techniques to achieve the GaN-on-diamond wafers for the fabrication of AlGaN/GaN HEMTs. The problems and challenges of each method are discussed. In addition, the effective thermal boundary resistance between GaN and diamond, which characterizes the heat concentration, is analyzed with regard to different integration and measurement methods.

A new technique of diamond and InGaP room temperature bonding in atmospheric air is reported. Diamond substrate cleaned with H2SO4/H2O2 mixture solution is bonded to InGaP exposed after removing the GaAs layer by the H2SO4/H2O2/H2O mixture solution. The bonding interface is free from interfacial voids and mechanical cracks. An atomic intermixing layer with a thickness of about 8 nm is formed at the bonding interface, which is composed of C, In, Ga, P, and O atoms. After annealing at 400 °C, no exfoliation occurred along the bonding interface. An increase of about 2 nm in the thickness of the atomic intermixing layer is observed, which plays a role in alleviating the thermal stress caused by the difference of the thermal expansion coefficient between diamond and InGaP. The bonding interface demonstrates high thermal stability to device fabrication processes. This bonding method has a large potential for bonding large diameter diamond and semiconductor materials.

AbstractNanodiamond (ND) has strong chemical stability, the initial oxidation temperature of ND is above 500 °C. A variety of oxygen-containing functional groups are adsorbed on the surface of ND, which makes ND has certain conductivity. Then ND can be used as highly stable catalyst or ideal support material. This paper reviews the properties, functionalization and electrochemical applications of ND. In this review, the catalytic activity and stability of diamond-based catalysts can be further improved by appropriately functionalizing ND, and the research progress in the field of electrochemistry can be increased.

The response property and stability of diamond Schottky barrier photodiodes (SBPDs) were investigated for the monitor applications of deep ultraviolet (DUV) light and high-energy radiation particles. The SBPDs were fabricated on the unintentionally doped insulating diamond epilayer grown on a heavily boron-doped p+-diamond (100) conductive substrate by microwave plasma chemical vapor deposition. The vertical-type SBPDs were constructed of semitransparent tungsten carbide (WC) Schottky contact on the top of the device and a WC/titanium ohmic contact on the bottom. The SBPDs were operated to detect the DUV light and protons in zero-bias photovoltaic mode. The spectral response of the SBPDs showed that the peak wavelength was at 182 nm with a sensitivity of 46 ± 1 mA/W. The response speed was shorter than 1 sec, with a negligible charge-up effect and persistent photoconductivity. The SBPDs showed a stable response upon the irradiation by 172-nm xenon excimer lamp with 70 mW/cm2 for 200 hrs and 70 MeV protons for the dose of 10 MGy, corresponding to a non-ionizing energy loss of 1.4 × 1016 MeV neq/cm2.

In this article, a series of highly boron-doped diamond ([B] > 1021 cm−3) electrodes with small gradient variations in boron concentration were prepared by hot filament chemical vapor deposition (HF-CVD). Reactive blue 19 (RB-19) dye solution was used as a prototype wastewater. Interestingly, we found that the electrochemical properties (electrochemically active surface area and oxygen evolution potential) and the electrochemical degradation performance did not deteriorate linearly with increasing boron concentration. Specifically, the electrochemically active surface area of the electrode at [B]/[C] = 50,000 ppm was the highest of 9.366 cm2, the chromaticity removal rate of RB-19 dye wastewater reached 100% after 90 min, and the TOC removal rate reached 74.48% after 180 min with the lowest energy consumption.

Investigation of germanium gate hydrogen-terminated (H-terminated) diamond field effect transistor (FET) with Al2O3 dielectric layer has been successfully performed. The device demonstrates a normally-on characteristics, whose maximum drain-source current density, threshold voltage, maximum transconductance, on/off ratio, subthreshold swing, capacitance, carrier density, saturation carrier mobility, fixed charge density and interface state density are of −37.3 mA/mm, 0.22 V, 6.42 mS/mm, 108, 134 mV/dec, 0.33 μF/cm2, 9.83 × 1012 cm−2, 97.9 cm2/V·s, 7.63 × 1012 cm−2 and 2.56 × 1012 cm−2·eV−1, respectively. This work is significant to the development of H-terminated diamond FET.

Aiming at developing inch-sized processing of diamond, B-doped layer was grown on mosaic single-crystallin diamond wafers by using hot-filament chemical vapor deposition (CVD), which is expected to have an advantage in terms of the deposition area compared with microwave plasma (MWP) CVD. Uniformity in horizontal and vertical directions is studied. It is found that the junctions of the monocrystalline diamond domains in the mosaic wafer and the direction of the crystal off-angles against to these junctions are less effective to the uniformity of the impurity concentrations. On the other hand, it is suggested that excess incorporation of W from the filament suppresses the growth and incorporation of B. It is shown that millimeter scale or more precise control of the arrangement of the wafer and the filament enables to obtain more uniform and efficient doping.