Diamond Growth Rate Research Articles

Free-standing n-type phosphorus-doped diamond

n-type diamond substrates are highly desired for diamond electronics and quantum technology based on NV centers. In this work, we investigate the high growth rates obtained using plasma with high-power densities in a commercial bell-jar chemical vapor deposition reactor equipped with a gas panel for diamond doping with phosphorus impurities. We evidence that the diamond growth rate is increased by adding phosphorus precursor in the gas mixture, up to 21.6 μm/h. We found conditions for growing extremely thick (up 580 μm) phosphorus doped (100) diamond homoepilayers keeping a n-type character as shown by optical spectroscopy. From such films we succeed in slicing a free-standing phosphorus-doped diamond plate, showing the feasibility of n-type diamond substrate fabrication for further use in optoelectronics and quantum devices.

Effect of hydrogen flow rate on the plasma state and quality of diamond crystals grown by MPCVD

The electronic application of diamond is still immature because of the relatively high density of dislocation. Hydrogen flow rate is one of the key parameters that determine the crystalline quality of diamond, but most of the previous works focus on the growth of polycrystalline diamond. Herein, the effects of hydrogen flow rate on the growth rate and crystalline quality of single crystal diamond have been evaluated while keeping the CH4/H2 ratio. It demonstrates that a medium H2 flow rate can balance the C2 concentration and nitrogen leakage in the chamber, resulting in the maximum of growth rate. Similarly, the dislocation density decreases firstly and then increases with a minimum value of 4 × 104/cm2 under a medium H2 flow rate. The variation of growth rate and dislocation density versus hydrogen flow rate can be double-confirmed from both high pressure and high temperature and chemical vapor deposition samples. The incline angle of step riser relative to the terrace is smaller than 20°, which helps to switch the propagation direction of dislocation towards the raiser region. A relatively wider step width under a medium H2 flow rate means a lower density of step riser region to display the dislocation. Therefore, we conclude that a medium hydrogen flow rate can effectively balance the crystalline quality and growth rate of the single crystal diamond.

Effect of oxygen doping on cutting performance of CVD diamond coated milling cutters in zirconia ceramics machining

Diamond thin films were deposited on WC-Co tools using the hot-filament chemical vapor deposition (HFCVD) technique at varying pressures and oxygen doping levels. As the oxygen doping content increased, the purity of the diamond phase improved, and the density of the <111> crystal plane on the film's surface increased. The growth rate of diamond films initially increased and then decreased under low pressure, with a corresponding decrease in residual compressive stress. Conversely, at high pressure, increased oxygen doping enhanced the diamond phase purity and growth rate while reducing residual compressive stress. Cutting experiments on pre-sintered zirconia ceramics for milling linear slots and engraving dentures demonstrated that diamond-coated milling cutters exhibited superior cutting performance under consistent oxygen and carbon source concentrations and stable air pressure conditions. The oxygen-doped diamond-coated milling cutter grown at a pressure of 1 KPa exhibited the longest service life, attributed to its reduced surface roughness, lower cutting force, and increased density of the <111> crystal plane orientation. This cutter could machine up to 1300 crowns, making it approximately 80% more durable than non‑oxygen-doped diamond-coated milling cutters and about 20 times more durable than uncoated ones.

Enhanced growth rates of N-type phosphorus-doped polycrystalline diamond via in-liquid microwave plasma CVD

Phosphorus-doped diamond (PDD) exhibits excellent properties, making it suitable for a wide range of applications, such as electronic devices and electrodes. Here, we report the first synthesis of PDD by in-liquid microwave plasma CVD (IL-MPCVD) under high-pressure and low-power conditions. A mixture of methanol (MeOH) and ethanol (EtOH) with triethyl phosphate ((C2H5)3PO4) and (P/C = 1000 ppm) was used for the PDD deposition. Samples were characterized by laser microscopy, Raman spectroscopy, and glow discharge optical emission spectroscopy. Notably, PDD was successfully produced at a growth rate of 280 μm/h, which is two orders of magnitude higher than conventional CVD methods. Additionally, cyclic voltammetry (CV) and impedance spectroscopy (EIS) were used to evaluate the electrochemical properties of PDD. As a result, we confirmed the wide potential window characteristic of conductive diamond and determined that the donor density was [P] = 3.8 × 1017cm⁻³. Therefore, it is clear that IL-MPCVD is applicable for very high growth rates in the CVD process for PDD synthesis.

A theoretical study on dopants substituted on the H-terminated surface regulating the threshold concentration of nitrogen for accelerating diamond growth

Nitrogen is widely believed to accelerate the diamond growth by chemical vapor deposition (CVD). While there is currently no consensus on the reaction mechanism of nitrogen increasing the growth rate of CVD diamond. In this work, we have proposed a chemical adsorption model formed by substitutional nitrogen on the H-terminated surface of diamond. The first principles calculations based on density functional theory are used to systematically study the effects of substitutional nitrogen on several key features (i.e., surface absorption energy, geometric structure, atomic charge, electron bond population, and electron density) of the H-terminated surfaces. The results indicate that nitrogen substituted on the H-terminated surface are probably more favorable for hydrogen desorption, which can not only affect the properties of directly bonding adjacent species, but also cause changes in the geometric and electronic properties around the surface by electron transfer or forming additional covalent bonds. Furthermore, compared with single nitrogen doping, the co-doped structures formed by adding boron or phosphorus at a relatively low N/H ratio on the H-terminated surface could enhance or weaken the stability of the diamond surface, that is, weaken or enhance the desorption process of hydrogen. It is therefore proved the existence of a regulatory effect on the threshold concentration required for nitrogen to accelerate diamond growth.

Low-Temperature Deposition of Diamond Films by MPCVD with Graphite Paste Additive

Modern integrated circuits (ICs) take advantage of three-dimensional (3D) nanostructures in devices and interconnects to achieve high-speed and ultra-low-power performance. The choice of electrical insulation materials with excellent dielectric strength, electrical resistivity, strong mechanical strength, and high thermal conductivity becomes critical. Diamond possesses these properties and is recently recognized as a promising dielectric material for the fabrication of advanced ICs, which are sensitive to detrimental high-temperature processes. Therefore, a high-rate low-temperature deposition technique for large-grain, high-quality diamond films of the thickness of a few tens to a few hundred nanometers is desirable. The diamond growth rate by microwave plasma chemical vapor deposition (MPCVD) decreases rapidly with lowering substrate temperature. In addition, the thermal conductivity of non-diamond carbon is much lower than that of diamond. Furthermore, a small-grain diamond film suffers from poor thermal conductivity due to frequent phonon scattering at grain boundaries. This paper reports a novel MPCVD process aiming at high growth rate, large grain size, and high sp3/sp2 ratio for diamond films deposited on silicon. Graphite paste containing nanoscale graphite and oxy-hydrocarbon binder and solvent vaporizes and mixes with gas feeds of hydrogen, methane, and carbon dioxide to form plasma. Rapid diamond growth of diamond seeds at 450 °C by the plasma results in large-grained diamond films on silicon at a high deposition rate of 200 nm/h.

Effect of sulfur and phosphorous doping on the growth rate of CVD diamond (111)

The purpose with the present study has been to theoretically investigate the effect of P (or S) doping on the chemical vapor deposition (CVD) growth rate of diamond. Density functional theory (DFT) calculations under periodic boundary conditions were then used for the investigation of the highly symmetric H-terminated diamond (111) surface. It was shown that both the thermodynamics and kinetics of P (or S) substitutional doping during diamond (111) growth were severely affected by the dopants (as compared with the non-doped situation).As a result of the thermodynamic calculations, except for P doping in C layer 1, the thermodynamic driving force for the diamond (111) growth was found to be largely improved by positioning P within the upper surface region of the H-terminated diamond (111) surface, while the opposite was true for S-doping. The P doping had a local vertical influence on the H abstraction energies, which was not the situation for the S doping. Also, both P and S doping showed a local lateral influence on the H abstraction energies, which was more pronounced for P doping.As a result of the kinetic calculations, the vertical and lateral P doping showed no local effect on the H abstraction energy barriers. In fact, these energy barriers became zero for P positioned in C layer 2 and downwards and were also zero for longer distances from the H adsorbate. On the other hand, the vertical S doping showed a local effect on the calculated barrier energies, but no lateral effect. The calculated energy barriers were zero for all surface H adsorbates on the H-terminated diamond (111) surface when S was positioned in the 4th atomic C layer. The different results for P doping versus S doping could be explained by the fact that S contains one electron extra and that P has a larger electronegativity value.Consequently, the results showed that P positioned in the upper diamond (111) surface lattice caused an enhancement in the diamond growth rate. The exception was the position in C atomic layer 1, for which both P doping and S doping had no effect on the diamond growth rate. On the other hand, a growth rate improvement was only found for S positioned in the 4th C layer. Due to the much higher (i.e., more positive) theoretical incorporation energies of S dopants versus P dopants in the diamond lattice, it has here been concluded that P doping is more effective than S doping in increasing the growth rate of the H-terminated diamond (111). Especially when considering that the H adsorbates are very mobile on this diamond surface, which has been shown by ab initio MD simulations at experimental CVD temperatures. These observations correlate well with experimental results.

The analysis of the effect of the pressurization block on diamond synthesis cavity by finite element method

The cubic press is a common high-pressure equipment, used in scientific research and industrial production of diamonds because of its large sample cavity, simple operation, low cost, and high production efficiency. However, the ultimate pressure of the cubic press is low, which can be increased by adding the pressurization block (PB) to the assembly. In this paper, the pressurization effect of differently-shaped PBs (circle pressurization block (CIPB), square pressurization block (SPB), square frustum pressurization block (SFPB), and concave pressurization block (COPB)) was compared by the finite element method (FEM) calculations. Although the bottom areas of these PBs were identical, the pressurization effect of COPBs was better than that of other PBs. The main reason was that the shape of the COPB better contained pyrophyllite and reduced its outward flow. FEM calculations were also used to investigate changes in the temperature and convection fields inside the assemblies using COPBs. The results showed that adding COPBs increased the temperature difference between the top and bottom of the catalyst, increased the catalyst's convection velocity, and ultimately accelerated the diamond growth rate.

Two-dimensional modeling of diamond growth by microwave plasma activated chemical vapor deposition: Effects of pressure, absorbed power and the beneficial role of nitrogen on diamond growth

A two-dimensional (2D(r, z)) self-consistent model developed and validated in previous studies of diamond deposition processes in microwave (MW) plasma activated chemical vapor deposition reactors is applied in a systematic study of ways in which the gas pressure (over the range p = 75–350 Torr) and absorbed power (P = 1–3 kW) affect the plasma parameters, species distributions and diamond deposition processes from a gas mixture (1%CH4/H2 with 60 ppm added N2) at substrate temperatures (Ts = 1073 and 1323 K) and diameters (ds = 32–100 mm). A more limited set of process conditions for a 0.006%N2/4%CH4/H2 gas mixture and Ts = 1038–1153 K are investigated also. The study traces variations in the global distributions of electron concentration, electron and gas temperature, absorbed power density, key species concentrations and the hydrocarbon interconversion reactions, with particular focus on the radial profiles of CH3 radical and H atom concentrations just above the substrate and on predicted diamond growth rates, G(r). The results and the trends revealed when varying p and P should help guide future optimizations of deposition regimes. The absorbed power density is shown to exhibit quite steep gradients in both the radial (r) and axial (z) directions. This, and the finding of significant power absorption beyond the glowing plasma region, limits the utility of the oft-quoted ‘averaged power density’ as a parameter. The modeling also highlights the essential 2D character of the hydrocarbon interconversion and diffusion transfer processes, which challenges the applicability of any 1D modeling of such MW plasmas. Trace additions of N2 to a MW plasma activated CH4/H2 gas mixture have negligible effect on the plasma parameters or chemistry yet are known to boost the diamond growth rate. A semi-empirical expression for G(r) is developed further to explicitly include the effects of added N2 and a new mechanistic picture presented to account for the observed N-induced enhancements in G. This picture invokes stable moieties such as that formed by CH2 insertion into a CN dimer bond on the 2 × 1 reconstructed (100) diamond surface as ‘anchor’ sites that enable shorter CH2 surface migration lengths and more step-edges for irreversible incorporation of such migrating groups on the growing diamond surface.

Nitrogen Investigation by SIMS in Two Wide Band-Gap Semiconductors: Diamond and Silicon Carbide

Diamond and Silicon Carbide (SiC) are promising wide band-gap semiconductors for power electronics, SiC being more mature especially in term of large wafer size (200 mm). Nitrogen impurities are often used in both materials for different purpose: increase the diamond growth rate or induce n-type conductivity in SiC. The determination of the nitrogen content by secondary ion mass spectrometry (SIMS) is a difficult task mainly because nitrogen is an atmospheric element for which direct monitoring of N± ions give no or a weak signal. With our standard diamond SIMS conditions, we investigate 12C14N- secondary ions under cesium primary ions by applying high mass resolution settings. Nitrogen depth-profiling of diamond and SiC (multi-) layers is then possible over several micrometer thick over reasonable time analysis duration. In a simple way and without notably modifying our usual analysis process, we found a nitrogen detection limit of 2x1017 at/cm3 in diamond and 5x1015 at/cm3 in SiC.

Oxygen Concentration Dependence in Microwave Plasma‐Enhanced Chemical Vapor Deposition Diamond Growth in the (H, C, O, N) System

The dependence of nitrogen incorporation and crystalline quality of the nitrogen‐doped single‐crystal diamond on oxygen concentration is investigated. Nitrogen‐doped diamond is grown by microwave plasma‐enhanced chemical vapor deposition in the (H, C, O, N) system. Nitrogen concentration (N/H) and methane concentration (CH4/H2) are fixed at 100 ppm and 4%, respectively. Oxygen concentration (O/C) is controlled from 12.5 to 50% (O/H = 0.25–1%). The growth rate of diamond decreases from 38 to 7 μm h−1. The nitrogen concentration in the epitaxial layer increases with increasing oxygen concentration and starts to decrease when O/C &gt; 25% (O/H &gt; 0.5%). The full width at half maximum (FWHM) of the Raman peak at 1332 is 2.0–2.2 cm−1. Introduction of oxygen affects incorporation of nitrogen into diamond. There is an optimum value of oxygen concentration to give the highest nitrogen concentration. This is attributed to the enhancement of the effective concentration of nitrogen‐related species in the gas phase and reduction of the growth rate both due to oxygen introduction. The results suggest that the (H, C, O, N) system could give higher concentration of nitrogen than that of the (H, C, N) system without degradation of the crystal quality.

Self-consistent modeling of microwave activated N2/CH4/H2 (and N2/H2) plasmas relevant to diamond chemical vapor deposition

The growth rate of diamond by chemical vapor deposition (CVD) from microwave (MW) plasma activated CH4/H2 gas mixtures can be significantly enhanced by adding trace quantities of N2 to the process gas mixture. Reasons for this increase remain unclear. The present article reports new, self-consistent two-dimensional modeling of MW activated N2/H2 and N2/CH4/H2 plasmas operating at pressures and powers relevant to contemporary diamond CVD, the results of which are compared and tensioned against available experimental data. The enhanced N/C/H plasma chemical modeling reveals the very limited reactivity of N2 under typical processing conditions and the dominance of N atoms among the dilute ‘soup’ of potentially reactive N-containing species incident on the growing diamond surface. Ways in which these various N-containing species may enhance growth rates are also discussed.

High growth rate synthesis of diamond film containing perfectly aligned nitrogen-vacancy centers by high-power density plasma CVD

Diamond film sensors with large volumes that are synthesized by microwave plasma chemical vapor deposition (MPCVD) and contain perfectly aligned nitrogen-vacancy (NV) ensembles are promising material for achieving highly sensitive quantum magnetometers. The step-flow growth mode of MPCVD on diamond (111) surface is required to realize aligned NV center ensembles. However, it is difficult to control the growth mode on diamond (111) surface due to the presence of twins and the conventional growth rate of aligned NV center ensembles is lower than 0.5 μm/h. In this study, we achieved a high growth rate (6.6 μm/h) of diamond (111) film containing perfectly aligned NV ensembles with high contrast (30%) by applying high power density plasma (103 W/cm3) and precisely controlling the gas flow rate ratios of CH4/H2 and N2/CH4. The growth mode was controlled to realize step flow growth by inducing the hydrogen etching of the nucleation with decreasing the CH4/H2. It was considered that increasing the microwave power density produces a large amount of atomic hydrogen and carbon precursor, leading to a high growth rate of perfectly aligned NV center diamond film. By controlling the N2/CH4 ratio, the nitrogen density in the diamond film could be precisely controlled to obtain a high contrast. Moreover, we measured the quality of the obtained diamond sensor films using the ODMR spectra and Ramsey sequence. We confirmed a high Rabi contrast (approximately 30%) and no significant decrease in T2∗ due to the deterioration of the crystallinity of the diamond film was observed. This result is promising for building material technology for highly sensitive quantum sensors with large sensor volumes.

High-pressure synthesis and characterization of diamond from europium containing systems

Experimental studies have been carried out on diamond synthesis in Mg-based systems with additions of europium in various charge states, including Eu0, Eu2+, and Eu3+. The experiments were carried out at a pressure of 7.8 GPa and a temperature of 1800 °C. Metallic Eu, Eu-oxalate, Eu-carbonate, Eu2O3, EuCl3, EuF3, and EuF2 were used as additives. The influence of the content of Eu-containing compounds on diamond crystallization and the photoluminescence characteristics of synthesized diamonds was determined. The addition of europium compounds to Mg-based systems in all cases had an integral inhibitory effect on the diamond crystallization process, which manifested in a decrease in the degree of graphite conversion to diamond, a decrease in the diamond growth rate, and the appearance of metastable graphite. It was found that the inhibiting ability of europium compounds decreased in the following sequence: Eu-oxalate > Eu-carbonate > EuCl3 > Eu2O3 > metallic Eu > EuF3 > EuF2. Spectroscopic studies of the synthesized diamonds revealed a new defect center manifesting in photoluminescence as an optical system with a zero-phonon line structure at 502 nm. The center was tentatively assigned to defects involving Eu impurities and the main factors controlling the formation of the 520 nm center were determined.

Insight into temperature impact of Ta filaments on high-growth-rate diamond (100) films by hot-filament chemical vapor deposition

To improve the growth rate of diamond films, we grew single-crystalline (100) diamond films by hot-filament chemical vapor deposition (HFCVD), and investigated their growth mechanism. The methane/hydrogen concentration (CH4/H2) dependence of the growth rate was evaluated at a filament temperature of 3000 °C. The growth rate reached 17.9 μm/h at CH4/H2 = 5% and saturated at higher CH4/H2. We then investigated the filament-temperature dependence of the CH4 reaction rate at CH4/H2 = 5% (at which the methane supply is sufficient). The growth rate decreased with inverse filament temperature, indicating that the growth rate is governed by reactions on the filament surface. From the Arrhenius plot, the activation energy of diamond growth was estimated as 440 kJ/mol, close to that of CH4 → CH3⁎ + H⁎ decomposition. This result indicates that decomposition of CH4 and the formation of CH3 by the filament surface affect the growth rate of HFCVD-grown diamond.

Unusual Dependence of the Diamond Growth Rate on the Methane Concentration in the Hot Filament Chemical Vapor Deposition Process

Although the growth rate of diamond increased with increasing methane concentration at the filament temperature of 2100 °C during a hot filament chemical vapor deposition (HFCVD), it decreased with increasing methane concentration from 1% CH4 –99% H2 to 3% CH4 –97% H2 at 1900 °C. We investigated this unusual dependence of the growth rate on the methane concentration, which might give insight into the growth mechanism of a diamond. One possibility would be that the high methane concentration increases the non-diamond phase, which is then etched faster by atomic hydrogen, resulting in a decrease in the growth rate with increasing methane concentration. At 3% CH4 –97% H2, the graphite was coated on the hot filament both at 1900 °C and 2100 °C. The graphite coating on the filament decreased the number of electrons emitted from the hot filament. The electron emission at 3% CH4 –97% H2 was 13 times less than that at 1% CH4 –99% H2 at the filament temperature of 1900 °C. The lower number of electrons at 3% CH4 –97% H2 was attributed to the formation of the non-diamond phase, which etched faster than diamond, resulting in a lower growth rate.

Engineering quantum-coherent defects: The role of substrate miscut in chemical vapor deposition diamond growth

The engineering of defects in diamond, particularly nitrogen-vacancy (NV) centers, is important for many applications in quantum science. A materials science approach based on chemical vapor deposition (CVD) growth of diamond and in situ nitrogen doping is a promising path toward tuning and optimizing the desired properties of the embedded defects. Herein, with the coherence of the embedded defects in mind, we explore the effects of substrate miscut on the diamond growth rate, nitrogen density, and hillock defect density, and we report an optimal angle range for the purposes of engineering coherent ensembles of NV centers in diamond according to our growth parameters. We provide a model that quantitatively describes hillock nucleation in the step-flow regime of CVD growth, shedding insight on the physics of hillock formation. We also report significantly enhanced incorporation of nitrogen at hillock defects, opening the possibility for templating hillock-defect-localized NV center ensembles for quantum applications.

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.

Crystallization of Diamond from Melts of Europium Salts

Diamond crystallization in melts of europium salts (Eu2(C2O4)3·10H2O, Eu2(CO3)3·3H2O, EuCl3, EuF3, EuF2) at 7.8 GPa and in a temperature range of 1800–2000 °C was studied for the first time. Diamond growth on seed crystals was realized at a temperature of 2000 °C. Spontaneous diamond nucleation at these parameters was observed only in an Eu oxalate melt. The maximum growth rate in the europium oxalate melt was 22.5 μm/h on the {100} faces and 12.5 μm/h on the {111} faces. The diamond formation intensity in the tested systems was found to decrease in the following sequence: Eu2(C2O4)3·10H2O &gt; Eu2(CO3)3·3H2O &gt; EuF3 &gt; EuF2 = EuCl3. Diamond crystallization occurred in the region of stable octahedral growth in melts of Eu3+ salts and in the region of cubo-octahedral growth in an EuF2 melt. The microrelief of faces was characterized by specific features, depending on the system composition and diamond growth rate. In parallel with diamond growth, the formation of metastable graphite in the form of independent crystals and inclusions in diamond was observed. From the spectroscopic characterization, it was found that diamonds synthesized from Eu oxalate contain relatively high concentrations of nitrogen (about 1000−1200 ppm) and show weak PL features due to inclusions of Eu-containing species.

Investigation of homoepitaxial growth by microwave plasma CVD providing high growth rate and high quality of diamond simultaneously

Single crystal diamond (SCD) growth on (100)-oriented high-pressure high-temperature (HPHT) type 2a diamond substrate was investigated to optimize growth conditions providing high growth rate and high quality of diamond simultaneously. CVD operating regime for SCD synthesis was determined which allows achieving the highest possible growth rate and at the same time the minimum number of defects in diamond at minimum amount of nitrogen (less than 200 pbb) in the reactor. At the optimized microwave plasma CVD growth condition at high power density the formation of non-epitaxial diamond crystallites or hillocks or polycrystalline diamond rim around the SCD top surface was prevented. The high power density was achieved with a relatively low gas pressure of 160 Torr due to local electric field amplification above the substrate holder with projection. High quality SCD grown with a relatively high growth rate in the range of 6−8 μm/h at a microwave power of 3 kW and a temperature of 900 °C was obtained. It was found that the formation of surface defects could be effectively suppressed by choosing the misorientation angle of the substrate surface. At this angle the step-flow growth regime was implemented. By choosing the misorientation angle, CH4/H2 ratio and the power density or the concentration of atomic hydrogen the high quality SCDs of 1 mm thickness were successfully grown.