High Quality Single Crystal Diamond Research Articles

High-performance single crystal diamond pixel photodetector with nanosecond rise time for solar-blind imaging

Solar-blind ultraviolet imaging detector is widely applied in many commercial and military fields, such as missile warning, guidance, ultraviolet communication, biomedical analysis, and police reconnaissance. High-performance pixel photodetector is the core of imaging technology. Therefore, its construction attracts intensive attentions in recent years. In this work, 8 × 8 planar pixels were constructed on high quality single crystal diamond using ultraviolet direct writing lithography. A typical pixel photodetector in metal-semiconductor-metal (MSM) structure achieved outstanding photo-response properties of a low dark current of 10−13–10−12 A at 50 V, a high light-dark current switching ratio over 105), a high responsivity of 22.6 A/W, and a decent specific detectivity of 4.2 × 1014 Jones. Moreover, the detector has a fast response time of 13 ns. Additional optoelectronic studies demonstrate the strong homogeneity and repeatability of the photodetectors array, enabling it to serve as a reliable solar-blind imaging photodetector with high spatial resolution.

Precision machining of single crystal diamond cutting tool via picosecond laser irradiation

Due to its high hardness and excellent wear resistance, single crystal diamond has been widely applied in mechanical processing. However, the outstanding hardness leads to great difficulties in the machining of diamond by traditional strategies. In this study, a synchronous feed laser method is developed to realize low damage, high efficiency, and high precision machining of single crystal diamond cutting tools. The disadvantages of traditional direct laser machining, including fullerene residue, bending behavior, and the plasma-shield effect, are well avoided by the good control of the scanning path during the laser fabrication, which enlarges the entrance of the kerf and reduces the air pressure inside the kerf. The synchronous feed laser machining can realize the remarkable increase of kerf depth at high speed, as well as a minimum roughness of ∼147 nm on the cutting surface. It provides a novel, high efficiency, and high precision strategy for the preparation of high quality single crystal diamond tools.

High charge collection efficiency detector based on plasma purified high-quality diamond

Diamond radiation detector is an ideal choice for the next-generation radiation detection in harsh environments, due to its small size, high irradiation resistance and fast response. However, high-purity single crystal diamond is hard to be prepared at the high growth rate due to the inevitable impurity incorporation. In this paper, based on the high-quality high-temperature/high-pressure (HPHT) single crystal diamond substrate, detector-grade single crystal diamonds material with high purity and low defect density were epitaxially grown at growth rate of about 4 μm/h by using plasma environment purification technology. It showed that the full width at half maximum of X-ray rocking curve of high-quality single crystal diamond could reach 0.007°, there was no nitrogen related impurity in PL spectrum, and the substitutional nitrogen content estimated by UV absorption spectrum was less than 10 ppb. After metallization and packaging process, the diamond detectors were prepared and the detector response under irradiation with 241 Am α-particles was realized. For the sample with fewer dislocations, the charge collection efficiency and energy resolution of this detector were 86.8 % and 7.85 % for electrons, and 96.7 % and 2.48 % for holes. The product of mobility and lifetime of electrons and holes were 1.7 × 10 −4 cm 2 V −1 and 3.7 × 10 −4 cm 2 V −1 , respectively. The high performances of the detector indicate that the current diamond detector can meet the application requirements of commercial diamond detectors. • Detector-grade diamond was prepared by plasma environment purification technology. • The high-purity single crystal diamond was grown at growth rate of about 4 μm/h. • The diamond detector with charge collection efficiency of 96.7 % was realized. • The products of mobility and lifetime of electrons and holes were 1.7 × 10 −4 and 3.7 × 10 −4 cm 2 V −1 .

High-rate growth of single-crystal diamond with an atomically flat surface by microwave plasma chemical vapor deposition

High quality single crystal diamond builds the foundation for the applications in high-power, high-frequency electronic devices. In this paper, high-quality (100) single-crystal diamond film grown by microwave plasma chemical vapor deposition (MPCVD) was studied. By optimizing the pre-etching process before growth, where the distance between the substrate and plasma plays an important role, high-quality chemical vapor deposition (CVD) diamond layer with a smooth surface can be acquired. The root-mean-square roughness of CVD diamond surface was reduced to 0.2 nm ∼ 0.5 nm within 5 μm × 5 μm area while maintaining the growth at a high rate of 3 μm/h ∼ 30 μm/h. The sheet resistance of the CVD diamond layer was 6.1 kΩ/sq by transmission line method, indicating a high potential to fabricate high-performance hydrogen-terminal diamond-based electronic devices.

Optimization of diamond optomechanical crystal cavities

Due to recent development of growing and processing techniques for high-quality single crystal diamond, the large scale production of diamond optomechanical crystal cavities has become feasible, enabling optomechanical devices that can operate in higher mechanical frequencies and can be coupled to two-level systems based on diamond color centers. In this paper we describe a design optimization method to produce diamond optomechanical crystal cavities operating at the high-cooperativity regime (close to unity) at room temperature.

A novel visible-light catalyzed assisted single crystal diamond chemical mechanical polishing slurry and polishing mechanism

Single crystal diamond has significant chemical and mechanical stability, which makes it challenging to efficiently obtain high quality single crystal diamond surface. In this study, the effect of four different sets of chemical mechanical polishing (CMP) slurries on the surface roughness Ra and the material removal rate MRR was investigated. The optimum slurry consisted of hydrogen peroxide, diamond micro-powder, synthesis product of nanodiamond and CuFe-layered double hydroxide (ND/LDH), oxalic acid and deionized water. After CMP by the optimum slurry, the average Ra value of three scanning ranges of 868 µm× 868 µm was 0.112 ± 0.003 nm and the average MRR value of three measurements was 416 ± 5 nm/h. High efficiency to obtain high quality single crystal diamond surface was achieved. The variation of hydroxyl radicals (·OH) concentration in the optimum slurry with time was measured. The optimum slurry CMP mechanism was elucidated by X-ray diffractometry (XRD) and X-ray photoelectron spectrometer (XPS). Visible-light photoelectrons and the rapid oxidation of C2O4·- radicals were accelerated the redox cycle of Fe3+/Fe2+ and Cu2+/Cu+ to produce·OH. The·OH oxidised the C atoms on the single crystal diamond surface to form -C-O-C-, -C-O-H and -CO. Finally, they were removed by diamond micro-powder abrasive, obtaining an ultra-smooth surface.

Synthesis of h-BN/diamond heterojunctions and its electrical characteristics

Conductive channel on the surface of hydrogen terminated diamond with two-dimensional h-BN passivation exhibits high hole mobility. However, the current h-BN passivated diamond mainly uses the method of mechanical peeling, which cannot achieve a large-size conductive channel and is difficult to meet the actual application requirements. In this study, the effect of classical transfer h-BN on the conductive channel on the surface of hydrogen terminated diamond is studied. High-quality single crystal diamond is epitaxially grown by microwave chemical vapor deposition (MPCVD) and the hydrogen terminated diamond is obtained by surface hydrogenation treatment. H-BN/H-diamond heterojunctions with different layers of h-BN are prepared by wetting transfer, and the characteristics of channel carrier transport are systematically studied. The results show that the channel conductivity is significantly enhanced after h-BN transfer, and with the increase of h-BN thickness, the enhancement effect of channel conductivity tends to be stable. The transfer of multilayer h-BN can increase the carrier density on the surface of hydrogen terminated diamond by nearly 2 times, and the square resistance is reduced to 50%. The current results show that the h-BN/H-diamond heterojunction may have a transfer doping effect, resulting in a significant increase in carrier density. With the increase of the channel carrier density, the channel mobility on the surface of the h-BN passivated diamond remains stable. The H-BN absorbs on the surface of the diamond, so that the negative charge originally on the surface of the hydrogen termination moves to the surface of h-BN, and the distance of action increases, weakening the coupling of the negative charge of the hole with the negative charge of the dielectric layer in the conductive channel of the hydrogen terminated diamond, which makes the mobility stable.

Simulation of diamond synthesis by microwave plasma chemical vapor deposition with multiple substrates in a substrate holder

To simulate the electric field distribution in a cylindrical resonant cavity during diamond crystal growth by microwave plasma chemical vapor deposition (MPCVD), a three-dimensional (3D) model, based on the electromagnetic field part of the finite element simulation solver COMSOL Multiphysics software, was established in this study. It was found that precise fillet treatment for the edge of the sample holder in the cavity can effectively improve the distribution of the electric field in this area, which is more conducive for the epitaxial growth of diamond. Based on the actual experimental requirements, nine diamond substrates were added to the holder with a previously processed edge fillet. By comparing with the simulated situation without substrates, it was proved that the addition of substrates influences the electric field distribution nearby. Furthermore, a new groove substrate holder with rounded corners was designed. Nine substrates with specific spacing were added to the groove holder, and the 3D and two-dimensional electric field distribution in this region were obtained. The optimized substrate holder makes the substrates less exposed to strong microwave plasma, which aids in high-quality single-crystal diamond synthesis. The simulation results were further verified experimentally.

Evolution of growth characteristics around the junction in the mosaic diamond

In order to realize the practical use of diamond as a semiconductor material, large-area single-crystal diamond wafers with uniform quality are required. Mosaic growth is an effective method to produce inch-grade single-crystal diamonds. However, the quality of the wafer is limited by the junction interface seriously, because cracking occurs easily due to the high internal stress. In this paper, the repetition growth method was adopted to grow mosaic splicing single-crystal diamond without polycrystalline diamond interface. The high-quality single crystal diamond slices were reduplicated by microwave plasma chemical vapor deposition (MPCVD). The substrates were obtained by cutting a piece of CVD diamond along a plane perpendicular to 〈001〉 (with a (100)-oriented surface). The evolution of the growth characteristics around the junction of the substrates at different stages was studied. The results show that the surface of the epitaxial layers gradually evolves from blurry terraces to a regular well-ordered step flow. When the substrates have the same deviation direction and the off-direction angles are within 3°, the junction of the substrates can connect smoothly. Raman mapping shows that there is a mixture of tensile stress and compressive stress near the junction. As the thickness of the epitaxial layer increases from 280 μm to 560 μm, the range of tensile stress near the joint area expands from 85 μm to 150 μm, the maximum tensile stress increases from 0.08 GPa to 0.16 GPa. In addition, the value of FWHM in the X-ray rocking curve is less than 2.80 cm−1 around the junction, which indicates good crystal quality.

High quality CVD single crystal diamonds grown on nanorods patterned diamond seed

Microwave plasma chemical vapor deposition (MPCVD) has been developed as a popular method to grow artificial single crystal diamonds with high crystal quality due to its feasibility and economical effectivity. However, the surface roughness and defects will lead to the generation of cracks in the growth process and significant degradation of the crystal quality of epitaxial CVD diamond. Although optimized growth parameters and subsequent chemico-mechanical polishing (CMP) could improve the surface morphology of CVD diamond layer for device fabrication, more investigations need to be done. In this study, nano-sized patterns were prepared by self-assembled Ni mask and inductively coupled plasma (ICP) etching method on diamond seed, and the height of nanorods were optimized for high quality single crystal diamond growth. According to the Microscope imaging, Raman spectroscopy, photoluminescence (PL) mapping and X-ray diffraction measurements, the influence of diamond nucleation on nanorod structures has been evaluated. The results demonstrate that the surface morphology and crystal quality of CVD diamond layer can be improved by the nano-sized patterned diamond seed, indicating a promising method for diamond-based device fabrication.

Progress in semiconductor diamond photodetectors and MEMS sensors

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.

Recent Advances in Single Crystal Diamond Device Fabrication for Photonics, Sensing and Nanomechanics.

In the last two decades, the use of diamond as a material for applications in nanophotonics, optomechanics, quantum information, and sensors tremendously increased due to its outstanding mechanical properties, wide optical transparency, and biocompatibility. This has been possible owing to advances in methods for growth of high-quality single crystal diamond (SCD), nanofabrication methods and controlled incorporation of optically active point defects (e.g., nitrogen vacancy centers) in SCD. This paper reviews the recent advances in SCD nano-structuring methods for realization of micro- and nano-structures. Novel fabrication methods are discussed and the different nano-structures realized for a wide range of applications are summarized. Moreover, the methods for color center incorporation in SCD and surface treatment methods to enhance their properties are described. Challenges in the upscaling of SCD nano-structure fabrication, their commercial applications and future prospects are discussed.

Single crystal diamond growth by MPCVD at subatmospheric pressures

Microwave plasma assisted chemical vapor deposition (MPCVD) is the established technique to produce high quality single crystal diamond (SCD). While typical pressures for SCD growth regimes in methane-hydrogen plasma are currently within 100–300 Torr, a transition to much high pressures promises enhanced growth rates. Here, we report on successful SCD synthesis by MPCVD in CH4-H2 gas mixtures at pressures up to 600 Tорр. A strong change of the plasma shape and volume (the latter shrinks by 10 times at fixed MW power) with pressure rise from 100 to 600 Torr was observed, still keeping the plasma stable. The record high absorbed MW power density of ≈1800 W/cm3 was achieved at 600 Torr. Optical emission spectroscopy (OES) was used for the plasma analysis via monitoring emission intensities of radicals Hα, C2 and CH. The gas temperature Tg determined from analysis of rotational fine structure of OES Swan transitions of dimer C2 (516 nm) turned out to be essentially constant ∼ 3100 ± 150 K over the pressure range explored. The diamond growth rate is found to increase by an order of magnitude with pressure to achieve 57 μm/h at 500 Torr at relatively low (4%) CH4 concentration, as measured in situ using low-coherence interferometry, but declined at further pressure increase. The produced films were characterized with SEM, XRD, Raman and photoluminescence spectroscopy, and a high/moderate quality of the obtained material was confirmed.

高质量单晶金刚石的合成、结构与光学性能研究

高质量单晶金刚石的合成、结构与光学性能研究

Homoepitaxy Growth of Single Crystal Diamond under 300 torr Pressure in the MPCVD System.

The high-quality single crystal diamond (SCD) grown in the Microwave Plasma Chemical Vapor Deposition (MPCVD) system was studied. The CVD deposition reaction occurred in a 300 torr high pressure environment on a (100) plane High Pressure High Temperature (HPHT) diamond type II a substrate. The relationships among the chamber pressure, substrate surface temperature, and system microwave power were investigated. The surface morphology evolution with a series of different concentrations of the gas mixture was observed. It was found that a single lateral crystal growth occurred on the substrate edge and a systemic step flow rotation from the [100] to the [110] orientation was exhibited on the surface. The Raman spectroscopy and High Resolution X-Ray Diffractometry (HRXRD) prove that the homoepitaxy part from the original HPHT substrate shows a higher quality than the lateral growth region. A crystal lattice visual structural analysis was applied to describe the step flow rotation that originated from the temperature driven concentration difference of the C2H2 ion charged particles on the SCD center and edge.

High-quality single crystal diamond diffraction gratings fabricated by crystallographic etching.

We demonstrate a novel method for fabricating single crystal diamond diffraction gratings based on crystallographic etching that yields high-quality diffraction gratings from commercially available <100> diamond plates. Both V-groove and rectangular gratings were fabricated and characterised using scanning electron microscopy and atomic force microscopy, revealing angles of 57° and 87° depending on the crystal orientation, with mean roughness below Ra = 5 nm on the sidewalls. The gratings were also optically characterised, showing good agreement with simulated results. The fabrication method demonstrated in this contribution shows the way for manufacturing high-quality diamond diffractive components that surpass existing devices both in quality and manufacturability.

Research on band-edge emission properties and mechanism of high-quality single-crystal diamond

The band-edge emission properties from a homoepitaxial chemical vapor deposition single-crystal diamond have been studied in detail through photoluminescence (PL) measurement from room temperature down to 8 K. In particular, we firstly observed the third phonon replica of the intrinsic emission at 5.277 eV and the second phonon replica of the intrinsic emission at 5.330 eV in the PL spectra, indicating the high crystallinity of our diamond sample. The main optical characteristics of intrinsic recombination radiation for single crystal diamond at low temperatures have been reported and its light emission mechanism has been discussed in this paper.

Development of a plate-to-plate MPCVD reactor configuration for diamond synthesis

The design and performance of a microwave plasma chemical vapor deposition (MPCVD) reactor based on compressed microwave waveguides and plate-to-plate substrate holders are described. This reactor can be operated at pressures from 10 to 40kPa with microwave power of 0.4–1.2kW, and a high plasma power density up to 500W/cm3 can be obtained. The single-crystal diamond (lower substrate holder) and polycrystalline diamond (upper substrate holder) have been grown by the plate-to-plate MPCVD reactor using high pressure CH4-H2 mixture gases. Experimental results show that high quality single-crystal diamond and polycrystalline diamond were simultaneously synthesized at a growth rate of 25μm/h and 12μm/h, respectively. The results indicate that our MPCVD reactor is unique for the synthesis of diamond with high efficiency.

Analyses of single crystal diamond substrates grown in a pocket substrate holder via MPACVD

High quality single crystal diamond (SCD) substrates are required for several different important current applications. Microwave Plasma Assisted Chemical Vapor Deposition (MPACVD) is a convenient deposition method for high quality substrates. It is hence imperative to synthesize and analyze substrates grown via different CVD techniques. This paper describes the quality of single crystal diamond substrates which have been grown via one such deposition strategy, which is in a “pocket substrate holder” design. The growth process in such a holder helps in depositing substrates which have almost no polycrystalline diamond (PCD) rim growth. The exact pocket holder growth process at high pressures (240 Torr) and high microwave power densities (~ 500 W/cm3) has been discussed in a previous publication [1]. The SCD CVD substrates were analyzed with different characterization techniques. By synthesizing diamond substrates in a pocket holder, the lack of any/almost any PCD rim helped in reducing the amount of stress in the crystals. To study the electronic quality of the substrates, etching experiments were conducted to determine the etch pit density. Nomarski images confirm that the number of etch pits at the edges is higher than at the center of the etched surface thereby implying the feasibility of this simpler method of reducing the etch pit density. The pocket holder process thus not only reduces the PCD rim but also reduces the substrate etch pit density and hence shows good promise of delivering high quality substrates.

High-quality single-crystal diamond nanophotonic and nanomechanical resonators

High-quality single-crystal diamond nanophotonic and nanomechanical resonators