High-pressure Chemical Vapor Deposition Research Articles

Comparative analysis: CapEx in diamond mining versus diamond growing, based on open data sources and experimental results

The diamond industry has long been associated with environmental and social problems, ranging from mining practices to ethical concerns related to diamond sourcing. In recent years, there has been a growing interest in lab-grown diamonds as a sustainable alternative for diamond consumers. However, the production of lab-grown diamonds has own challenges. This article examines the capital expenditures per annualized carat of rough diamonds obtained through mining and two fabrication methods: high-pressure high-temperature (HPHT) and microwave plasma-assisted chemical vapour deposition (MP CVD). Lab-grown diamonds produced using HPHT and MP CVD methods require significantly higher capital expenditures per annualized carat compare to mined diamonds. HPHT diamonds require on-time CapEx of 500–833 US$ per carat annually, while MP CVD diamonds demand 549–1648 US$ per carat annually. Finding ways to reduce production cost and increase efficiency will be crucial in realizing the potential of lab-grown diamonds as a sustainable alternative to mined diamonds.

Numerical Analysis of a High-Pressure Spatial Chemical Vapor Deposition (HPS-CVD) Reactor for Flow Stability at High Pressures

Numerical Analysis of a High-Pressure Spatial Chemical Vapor Deposition (HPS-CVD) Reactor for Flow Stability at High Pressures

Basic characteristics of synthetic-diamond scintillator

To extend the use of diamond detectors to particle detail analysis and the development of radiation monitoring applications, we conducted a study on synthetic-diamond scintillators, which have so far not been sufficiently evaluated. To understand the basic characteristics of scintillators, we measured the luminescence characteristics of two types of commercially available synthetic diamonds manufactured via high-pressure high-temperature (HPHT) and chemical vapor deposition (CVD) methods. The color center of each diamond was identified by measuring the radio-luminescence spectrum under X-ray excitation, and the scintillation light waveform was measured by irradiating α-rays and β-rays. The light yield of the HPHT diamond with a nitrogen concentration less than 200 ppm had a higher emission than that of the CVD diamond with a nitrogen concentration of less than 1 ppm; the light yield for the former was estimated to be (5.5 ± 0.5) × 104 ph/MeV. Because of the significant light yield and physical properties of diamonds, unique particle detectors can be achieved.

Study on preparation and electromagnetic shielding properties of GNs/NaCl/SCF composite carbon foam

Herein, the graphenes/sodium chloride/sucrose composite carbon foam (GNs/NaCl/SCF) was prepared by high pressure pyrolysis and chemical vapor deposition (CVD) It was found that NaCl micron particles played the role of nucleating agent in the foaming process of sucrose based carbon foam, which could effectively tailoring the pore structure of composite carbon foam. When the thickness of GNs/NaCl/SCF is only 3 mm, the total shielding efficiency (SET) of composite carbon foam in the X-band range is up to 49.25 dB, and the absorption loss (SEA) is much greater than the reflection loss (SER). The SET of GNs/NaCl/SCF was 2.8 times higher than that of pure sucrose based carbon foam (SCF). This is due to the unique structure of the composite carbon foam. First, the rich 3D continuous pore cell structure of carbon foam improves the impedance matching degree of electromagnetic wave, so that the electromagnetic wave “trapped” in the pore cell, forming multiple reflection and scattering. Second, under the catalysis of elemental copper, the graphene grown in situ on the pore cell of the carbon foam formed a conductive network, which significantly improved the conductivity of the composite carbon foam. Third, the composite carbon foam has abundant heterogeneous interfaces (such as Cu-GNs, Cu-SCF, GNs-SCF, etc.), which act as the center of polarization of induce dipole polarization to further enhance the electromagnetic shielding performance. Sequentially, the synergistic effect of the above three aspects leads to the significant improvement of the electromagnetic shielding performance of composite carbon foam.

Nanostructured germanium synthesized by high-pressure chemical vapor deposition in mesoporous silica templates

Nanostructured germanium synthesized by high-pressure chemical vapor deposition in mesoporous silica templates

Nitrogen related paramagnetic defects: Decoherence source of ensemble of NV− center

We investigated spin-echo coherence times T2 of negatively charged nitrogen vacancy center (NV−) ensembles in single-crystalline diamond synthesized by either the high-pressure and high-temperature and chemical vapor deposition methods. This study specifically examined the magnetic dipole–dipole interaction (DDI) from the various electronic spin baths, which are the source of T2 decoherence. Diamond samples with NV− center concentration [NV−] comparable to those of neutral substitutional nitrogen concentration [Ns0] were used for DDI estimation. Results show that the T2 of the ensemble NV− center decreased in inverse proportion to the concentration of nitrogen-related paramagnetic defects [NPM], being the sum of [Ns0], [NV−], and [NV0], which is a neutrally charged state NV center. This inversely proportional relation between T2 and [NPM] indicates that the nitrogen-related paramagnetic defects of three kinds are the main decoherence source of the ensemble NV− center in the single-crystalline diamond. We found that the DDI coefficient of NVH− center was significantly smaller than that of Ns0, the NV0 center, or the NV− center. We ascertained the DDI coefficient of the NV− center DNV− through experimentation using a linear summation of the decoherence rates of each nitrogen-related paramagnetic defect. The obtained value of 89 μs ppm for DNV− corresponds well to the value estimated from the relation between DDI coefficient and spin multiplicity.

Spectroscopic Study of the 3107 cm−1 and 3143 cm−1 H-Related Defects in Type Ib Diamonds

Hydrogen-related infrared absorption bands in natural diamonds have been extensively investigated and widely used to identify natural, treated, and synthetic diamonds grown by high pressure and high temperature (HPHT) and chemical vapor deposition (CVD) techniques. However, the evolutional behavior of the hydrogen-related defects and the relationship between the hydrogen-related and nitrogen-related defects in natural and HPHT-treated Ib diamonds are unclear. In this article, the hydrogen-related defects, particularly the infrared absorption bands of 3107 cm−1 and 3143 cm−1 in natural type Ib diamonds and HPHT-treated natural diamonds, were systematically investigated using spectroscopic techniques. It was found that the 1405 cm−1 absorption intensity was directly proportional to the 3107 cm−1 absorption intensity; the 3143 cm−1 absorption intensity increased with the increase in the 3107 cm−1 absorption intensity, but there was no strict linear relationship between them. The 3143 cm−1 band was not only related to the intensity of the 3107 cm−1 but also related to the value of NC/NA in natural diamonds. When the value of NC/NA was less than one, the 3143 cm−1 band was more pronounced. After high-temperature annealing, the absorption intensities of the 3107 cm−1 and 3143 cm−1 in natural type Ib diamonds became stronger. However, in HPHT synthetic diamonds, only a 3107 cm−1 defect was introduced with the increase in the A centers in the diamonds. The difference and the detectability of the 3143 cm−1 and 3107 cm−1 bands investigated could be efficiently used to identify natural type Ib diamonds from their counterparts, including the synthetic diamonds and the HPHT-treated diamonds.

Structural, Compositional, and Thermal Stability Studies on In0.96ga0.04n Epilayers Grown by High Pressure Chemical Vapor Deposition

Structural, Compositional, and Thermal Stability Studies on In0.96ga0.04n Epilayers Grown by High Pressure Chemical Vapor Deposition

Chemical Vapor Deposition Single‐Crystal Diamond: A Review

With its outstanding physical properties, single‐crystal diamond is the material of choice for future power electronics and quantum devices. The later application field is based on the optical and spin properties of color centers hosted in diamond lattice. Two synthesis methods are currently developed to grow high‐quality diamond: high pressure and high temperature (HPHT) synthesis and chemical vapor deposition (CVD). Herein, the state of the art of single‐crystal diamond growth by CVD, either starting with diamond substrate (homoepitaxy) or controlling diamond epitaxial nucleation on a foreign substrate (heteroepitaxy) is described. Progress on substrates, dislocation propagation, and reduction of structural defects, doping, upscaling, and applications are reviewed. In light of recent progress, future challenges and the respective roles of homoepitaxial and heteroepitaxial materials in the applications roadmap are discussed.

Computational fluid dynamics modeling of a new high-pressure chemical vapor deposition reactor design

The design of a new super-atmospheric pressure metal organic chemical vapor deposition (MOCVD) reactor with spatially separated source zones and rotating susceptor is proposed and analyzed using computational fluid dynamics (CFD) techniques to determine fluid transport phenomena and suitability for thin-film synthesis of group III nitrides. This High-Pressure Spatial Chemical Vapor Deposition (HPS-CVD) reactor is designed to permit high-temperature growth of high-indium content group III nitrides. This is made possible by increasing the partial pressure of nitrogen by up to two orders of magnitude in the system thereby increasing decomposition temperatures of the group III nitride thin film. The effects of rector design, chamber height, system pressure, inlet flow rate, and rotational speed are investigated and discussed. Flow instabilities arising from the heated and rotating susceptor traversing separate source zones are minimized. Growth rates of group III nitride materials synthesized in an HPS-CVD reactor are estimated to be enhanced by approximately a factor of 10 compared to an existing super-atmospheric MOCVD reactor due to improved reactor design thereby providing comparable growth rates to current atmospheric MOCVD systems.

Synchrotron X-ray metrology of dopant distribution and oxidation state in high pressure CVD grown TM2+:ZnSe optical fibers

High pressure chemical vapor deposition (HPCVD) has shown to be a promising method for producing Cr2+:ZnSe and Fe2+:ZnSe mid-IR optical fiber lasers. The oxidation state of the dopants and their spatial homogeneity are critical for the characterization of effective fiber laser performance; however, this is challenging for small fiber cores and small doping concentrations. We demonstrate using synchrotron micro X-ray fluorescence (XRF) mapping to study the distribution of the dopants throughout the fiber cross-sections. Furthermore, we study the local chemical environment of these unique fiber structures using micro X-ray near edge absorption spectroscopy (XANES). Our study reveals that transition metal doped ZnSe deposited using HPCVD has nanoscale dopant aggregation although the material is chemically identical to the commercially produced diffusion doped laser crystals, as indicated by the presence +2 oxidation state of the dopants. This work demonstrates the power of synchrotron-based X-ray techniques for use as metrology tools for improving the performance of laser materials in fiber geometry.

Post-processing ZnSe optical fibers with a micro-chemical vapor transport technique

Polycrystalline zinc selenide optical fibers and fiber lasers are expected to provide powerful capabilities for infrared waveguiding and laser technology. High pressure chemical vapor deposition, which is the only technique currently capable of producing zinc selenide optical fibers, leaves a geometric imperfection in the form of a central pore which is detrimental to mode quality. Chemical vapor transport with large temperature and pressure gradients not only fills this central pore but also encourages polycrystalline grain growth. Increased grain size and a reduction in defects such as twinning are demonstrated with transmission electron microscopy, Raman spectroscopy, and X-ray diffraction, supporting that high-quality material is produced from this method. Finally, the mode structure of the waveguide is improved allowing most of the guided optical intensity to be centrally positioned in the fiber core. Loss as low as 0.22 dB/cm at 1908nm is demonstrated as a result of the material improvement.

Continuous wave Fe2+:ZnSe mid-IR optical fiber lasers.

Today fiber lasers in the visible to near-infrared region of the spectrum are well known, however mid-infrared fiber lasers have only recently approached the same commercial availability and power output. There has been a push to fabricate optical fiber lasers out of crystalline materials which have superior mid-IR performance and the ability to directly generate mid-IR light. However, these materials cannot currently be fabricated into an optical fiber via traditional means. We have used high pressure chemical vapor deposition (HPCVD) to deposit Fe2+:ZnSe into a silica optical fiber template. These deposited structures have been found to exhibit laser threshold behavior and emit CW mid-IR laser light with a central wavelength of 4.12 µm. This is the first reported solid state fiber laser with direct laser emission generated beyond 4 µm and represents a new frontier of possibility in mid-IR laser development.

Diamond encapsulated silicon optical fibers synthesized by chemical vapor deposition

Semiconductor optical fibers encapsulated in a protective diamond coating can theoretically lead to immense power handling capabilities and infrared functionality. Here, silicon optical fibers are grown using high pressure chemical vapor deposition before being coated by 50 μm–300 μm of diamond by microwave plasma-assisted chemical vapor deposition. This coating extends conformally around the fiber cross section with diamond crystallites in the film on the order of several micrometers. Complete coating of high-quality diamond around the fiber is indicated by scanning electron microscopy and Raman measurements. The encapsulated silicon fibers are durable enough to survive the diamond deposition process, as demonstrated by their ability to guide infrared light.

Chromium doped zinc selenide optical fiber lasers

The optical fiber geometry is known for rugged, high power laser sources that are preferred for many applications, but is typically limited to the visible and near-infrared regions of the electromagnetic spectrum due to the transmission limits of silica (< 2 µm). This wavelength range could be extended into the mid-infrared using transition metal doped, crystalline II-VI optical gain media, but these materials cannot be fabricated into optical fibers using conventional glass drawing methods. An in-situ high pressure chemical vapor deposition method for the fabrication of silica-cladded ZnSe fiber cores uniformly doped with Cr 2 + is reported. Optical pumping experiments reveal that these doped fibers exhibit threshold behavior and thus function as mid-infrared optical fiber lasers. Finite element calculations show that undesirable thermal effects common in bulk II-VI crystals are mitigated in the fiber geometry.

Fourier Transform Limited Linewidth of Optical Transitions in Single SiV Centers in “Adamantane” Nanodiamonds

Silicon-vacancy (SiV) color centers in diamond offer a promising system for quantum information applications owing to their intense narrowband emission and optically detectable spin states. Here, the fluorescent properties of ensembles and single SiV centers in diamonds obtained by high-pressure high-temperature synthesis from adamantane (below referred to as adamantane diamonds) are investigated at liquid-helium temperatures. Ensembles of SiV centers (~103) are studied in large diamond crystals (1–2 µm in size). Despite the large number of excited centers, the fine structure of the zero-phonon line, corresponding to four allowed optical transitions between the ground- and excited-state doublets of the SiV center, can be observed in the fluorescence spectra of these crystals. The width of individual lines is in the range of 60–80 GHz, which is explained by their inhomogeneous broadening. Single SiV centers are studied in diamond crystallites with sizes of about 200 nm. The width of the narrowest transition lines observed in the fluorescence spectra of single SiV centers under resonant excitation is almost three orders of magnitude smaller than linewidths in the spectra of SiV ensembles and is as small as 94 MHz; i.e., these lines are so narrow that their width is determined by the lifetime of the upper state of the transition. Therefore, adamantane nanodiamond features the narrowest emission line width of a single SiV center at cryogenic temperatures among other types of SiV-con-taining nanodiamonds of similar sizes obtained by the high-pressure high-temperature and chemical vapor deposition techniques.

Nitrogen in Diamond

Nitrogen is ubiquitous in both natural and laboratory-grown diamond, but the number and nature of the nitrogen-containing defects can have a profound effect on the diamond material and its properties. An ever-growing fraction of the supply of diamond appearing on the world market is now lab-grown. Here, we survey recent progress in two complementary diamond synthesis methods-high pressure high temperature (HPHT) growth and chemical vapor deposition (CVD), how each is allowing ever more precise control of nitrogen incorporation in the resulting diamond, and how the diamond produced by either method can be further processed (e.g., by implantation or annealing) to achieve a particular outcome or property. The burgeoning availability of diamond samples grown under well-defined conditions has also enabled huge advances in the characterization and understanding of nitrogen-containing defects in diamond-alone and in association with vacancies, hydrogen, and transition metal atoms. Among these, the negatively charged nitrogen-vacancy (NV-) defect in diamond is attracting particular current interest in account of the many new and exciting opportunities it offers for, for example, quantum technologies, nanoscale magnetometry, and biosensing.

Conformal coating of amorphous silicon and germanium by high pressure chemical vapor deposition for photovoltaic fabrics

Conformally coating textured, high surface area substrates with high quality semiconductors is challenging. Here, we show that a high pressure chemical vapor deposition process can be employed to conformally coat the individual fibers of several types of flexible fabrics (cotton, carbon, steel) with electronically or optoelectronically active materials. The high pressure (∼30 MPa) significantly increases the deposition rate at low temperatures. As a result, it becomes possible to deposit technologically important hydrogenated amorphous silicon (a-Si:H) from silane by a simple and very practical pyrolysis process without the use of plasma, photochemical, hot-wire, or other forms of activation. By confining gas phase reactions in microscale reactors, we show that the formation of undesired particles is inhibited within the microscale spaces between the individual wires in the fabric structures. Such a conformal coating approach enables the direct fabrication of hydrogenated amorphous silicon-based Schottky ...

Characterization of 880 V Normally Off GaN MOSHEMT on Silicon Substrate Fabricated With a Plasma-Free, Self-Terminated Gate Recess Process

In this paper, we report the device performance of a high-voltage enhancement-mode (E-mode) GaN MOSHEMT on silicon substrate. Normally off operation is realized by a self-terminated precision gate recess process on an optimized high-electron mobility transistor structure. The GaN MOSHEMT is fully pinched off at zero gate bias, suggesting a “true” normally off operation. The threshold voltage is 0.4 V with a drain current density of 1 $\mu \text{A}$ /mm as the criteria. The device with 15- $\mu \text{m}$ gate-drain distance and 100- $\mu \text{m}$ gate width exhibits a maximum drain current of 356 mA/mm at 8-V gate bias. The on/off current ratio of the device is larger than 1010 with a subthreshold slope of 80 mV/dec. The gate leakage current is below 10−7 mA/mm up to 9-V gate bias. The off-state breakdown voltage (BV) is as high as 1528 V (880 V) measured with floating (grounded) silicon substrate at a drain leakage current criterion of 5 $\mu \text{A}$ /mm. The specific on-resistance ( ${R}_{\text {ON,SP}}$ ) of the device is 2.79 $\text{m}\Omega \cdot$ cm2, and the power figure of merit (BV2/ ${R}_{ \text {ON,SP}}$ ) is 277 MW/cm2. High-voltage pulsed I–V measurement indicates that the dynamic on-resistance is only 1.6 times the static one with a pulsewidth of 10 $\mu \text{s}$ at 400-V off-state quiescent drain bias. The high performance of the normally off GaN MOSHEMT is supposed to benefit from the high quality low pressure chemical vapor deposition Si3N4 passivation layer and the advanced E-mode device fabrication process.

Kinetics of Silane Decomposition in High-Pressure Confined Chemical Vapor Deposition of Hydrogenated Amorphous Silicon

We study the kinetics of silane pyrolysis via confined high-pressure chemical vapor deposition (HPCVD) at pressures of 20–33 MPa in a microcapillary of 5.9 μm inner diameter. We find the growth rate to be first order with respect to silane concentration, with an activation energy of 53.7 ± 2.9 kcal/mol and a pre-exponential factor of 1.5 × 1010 m/s. The obtained activation energy is in the range of activation energies reported for hydrogen desorption from c-Si surfaces, suggesting that hydrogen desorption from the surface is the rate-limiting step in film growth. To further investigate this finding, reactive molecular dynamics simulations of thermal decomposition of silane on clean and hydrogen-passivated c-Si were performed. Homogeneous reactions were not observed in any of the simulations, in support of the hypothesis that heterogeneous silane decomposition on the silicon surface is the dominant mechanism for film deposition. In silane pyrolysis simulations on clean c-Si surfaces, almost all available s...