Chemical Vapor Deposition Diamond Growth Research Articles

Monitoring of the Initial Stages of Diamond Growth on Aluminum Nitride Using In Situ Spectroscopic Ellipsometry.

The high thermal conductivity of polycrystalline diamond makes it ideally suited for thermal management solutions for gallium nitride (GaN) devices, with a diamond layer grown on an aluminum nitride (AlN) interlayer atop the GaN stack. However, this application is limited by the thermal barrier at the interface between diamond and substrate, which has been associated with the transition region formed in the initial phases of growth. In this work, in situ spectroscopic ellipsometry (SE) is employed to monitor early-stage microwave plasma-enhanced chemical vapor deposition diamond growth on AlN. An optical model was developed from ex situ spectra and applied to spectra taken in situ during growth. Coalescence of separate islands into a single film was marked by a reduction in bulk void fraction prior to a spike in sp2 fraction due to grain boundary formation. Parameters determined by the SE model were corroborated using Raman spectroscopy and atomic force microscopy.

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 > 25% (O/H > 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.

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.

Perfect alignment and preferential orientation of nitrogen-vacancy centers during chemical vapor deposition diamond growth on (111) surfaces

Synthetic diamond production is a key to the development of quantum metrology and quantum information applications of diamond. The major quantum sensor and qubit candidate in diamond is the nitrogen-vacancy (NV) color center. This lattice defect comes in four different crystallographic orientations leading to an intrinsic inhomogeneity among NV centers, which is undesirable in some applications. Here, we report a microwave plasma-assisted chemical vapor deposition diamond growth technique on (111)-oriented substrates, which yields perfect alignment (94% ± 2%) of as-grown NV centers along a single crystallographic direction. In addition, clear evidence is found that the majority (74% ± 4%) of the aligned NV centers were formed by the nitrogen being first included in the (111) growth surface and then followed by the formation of a neighboring vacancy on top. The achieved homogeneity of the grown NV centers will tremendously benefit quantum information and metrology applications.

Diamond growth by chemical vapour deposition

This paper reviews the growth of diamond by chemical vapour deposition (CVD). It includes the following seven parts: (1) Properties of diamond: this part briefly introduces the unique properties of diamond and their origin and lists some of the most common diamond applications. (2) Growth of diamond by CVD: this part reviews the history and the methods of growing CVD diamond. (3) Mechanisms of CVD diamond growth: this part discusses the current understanding on the growth of metastable diamond from the vapour phase. (4) Characterization of CVD diamond: we discuss the two most common techniques, Raman and XRD, which have been intensively employed for characterizing CVD diamond. (5) CVD diamond growth characteristics: this part demonstrates the characteristics of diamond nucleation and growth on various types of substrate materials. (6) Nanocrystalline diamond: in this section, we present an introduction to the growth mechanisms of nanocrystalline diamond and discuss their Raman features.This paper provides necessary information for those who are starting to work in the field of CVD diamond, as well as for those who need a relatively complete picture of the growth of CVD diamond.

Enhanced control of diamond nanoparticle seeding using a polymer matrix

We have improved the diamond nanoparticle seeding approach for chemical vapor deposition diamond growth in a novel process that consists of embedding the nanoparticles into a polymer matrix. We used a thin film of polyvinyl alcohol (PVA) doped with nanoparticles, which burns away during the initial stages of growth, leaving a stable distribution of nanoparticles on the substrate to initiate growth. The study shows that by varying the initial concentration of nanoparticles in the polymer preparation, it is possible to control the density of nanoparticles on the surface, over a wide range of densities. In some experimental conditions, the high densities of diamond seeding values obtained compare well with the highest values reported by the state-of-the-art. Moreover, the technique also opens up the route to very large area seeding, and this onto most types of substrates. In situ x-ray photoelectron spectroscopy (XPS) analyses showed that after pyrolysis of the polymer under H2 plasma, no significant residual carbon from the polymer was observed. Also, in the case of growth on silicon substrates, no silicon carbide was observed at the surface, showing that no reaction takes place between the polymer and the silicon surface itself. Finally, XPS also demonstrated that the polymer has not modified significantly the surface of the diamond nanoparticles after its pyrolysis. This approach improves the reproducibility of diamond nanoparticle seeding on flat surfaces and is more versatile as it may be applied to complex three-dimensional structures or cavities.

Effect of Substitutional N on Important Chemical Vapor Deposition Diamond Growth Steps

This study analyses theoretically the effects of substitutional N on three different chemical vapor deposition diamond growth steps. The investigation is based on density functional theory, using both cluster and periodic models. The reaction steps, assumed to be predominantly occurring during diamond growth, are (i) CH(2) insertion within a carbon dimer, (ii) H transfer from a neighboring surface carbon to an adsorbed CH(2), and (iii) surface migration of CH(2). Carbon atoms at various lateral positions are substituted by N within the second, third, and fourth carbon layers beneath the surface. Both reaction energies and barrier energies were for all reaction steps carefully calculated. For the CH(2) insertion into a carbon dimer, the reaction energy was found to be in principle unaffected by substitutional N. However, the activation energy for the CH(2) insertion reaction was with one exception observed to be significantly increased by the presence of substitutional N. The H migration reaction was only found to be sensitive to the lateral position of N in the carbon layers. The reaction is observed to be favored or disfavored depending on this lateral position. For the CH(2) migration reaction, the substitutional N was observed to increase the activation barriers and thereby negatively affect the reaction kinetics.

Simulation of nanodiamond and nanographite formation from molten carbon in the presence of hydrogen

Hydrogen plays a significant role in the formation of nanodiamond, terminating diamond surfaces, and removing $s{p}^{2}$-bonded atoms from the surface during chemical-vapor deposition diamond growth. However, there are only few calculations that simulate nanodiamond development directly and even less that do so in a hydrogen-containing environment. Recently, nanoscale graphitic layers embedded in amorphous carbon were observed experimentally. We report here on results from a comprehensive study of nanodiamond and nanographite formation from molten carbon in the presence of hydrogen under varied conditions of external pressure and cooling rate. We find that hydrogen-free nanodiamond crystals are precipitated more readily at increased melt densities and cooling rates, whereas slower cooling rates permit formation of graphitic layers.

Diamond growth in solid substrate from gaseous source

Diamond growth on iron-based materials is extremely important for mechanical and electrical applications because the iron-based materials are widely used in domestic science. In our previous study, chemical-vapor deposition diamond nucleation and subsequent film deposition have been precisely controlled by the residence time of the source gas, which is an essential parameter during chemical-vapor deposition diamond growth. In order to investigate the mechanism of diamond growth on the iron-based materials, the inside of the stainless-steel substrates has been investigated by observing the cross-sectional images after the substrates are fractured by halves. The diamond grains were confirmed in the inside of the stainless-steel substrates. At an optimum condition, diamond growth with high crystalline quality in stainless-steel substrates was identified by Raman spectroscopy and scanning electron microscopy.

Process for Buried Metallization in Diamond Film

This paper investigates methods of combining chemical vapor deposition diamond growth techniques with a physical vapor deposition technique and an ion-beam-enhanced deposition technique, respectively, to produce buried metallization of polycrystalline diamond films. The mechanical and electrical integrity of the insulating and conducting elements following metallization and diamond overgrowth is shown. Both methods are shown to have bonding strength sufficient to withstand tape lift-off. Diamond overgrowth is also shown, thus enabling buried metallized layers to be created. Electrical resistivity measurements on metallized layers and between metallization separated by diamond films are shown to be sufficient to allow the use of diamond as an insulating interlayer material for multilayer circuit boards.

The impact of inert gases on the structure, properties and growth of nanocrystallinediamond

For biomedical and electronic applications, it is highly desirable to depositsmooth diamond films with crystal sizes in the nanoscale range. We presentexperimental results of chemical vapour deposition diamond growth fromCH4 with incrementalsubstitution of H2 with He or Ar gases; the concentrations of the inert gases were varied between 0 and98 vol%. Results show that initially the addition of either argon or helium increases thegrowth rate and significantly alters the film structure and crystallinity up to 60 vol%. Withadditions of argon or helium greater than 60 vol% in the gas phase the growthdecreases and there is degradation of the crystal structure. In general, nanocrystallinediamond has been deposited at dilutions in excess of 90 vol% helium or argon.

Electrically active sulfur-defect complexes in sulfur implanted diamond

Single crystal type IIa 〈100〉 diamonds were implanted with sulfur, phosphorus, and argon ions under different implantation and annealing conditions. Shallow (sub-MeV) as well as deep (MeV) implantations into samples held at low (liquid nitrogen) ambient (room temperature) and high (400 °C) temperatures were employed. The implanted samples were subjected to postimplantation annealing up to 1000 °C. Following each processing step the samples were subjected to (i) Raman spectroscopy, in order to investigate the implantation related residual defects, and (ii) electrical (resistivity and sometimes Hall effect) measurements as function of temperature. The correlation between the results of these structural and electrical measurements and the comparison of results obtained under identical processing conditions for possible n-type dopant ion-implantations (S and P) and inert (Ar) ion-implantations, as controls, leads to the following conclusions: (a) Sulfur implanted samples always exhibit at least one order of magnitude higher conductivity than Ar control implanted samples. The activation energy associated with the S related conductivity is 0.32–0.37 eV whereas that of the Ar control is 0.5 to 0.6 eV. Hall effect shows, for selected cases, n-type conductivity with low carrier concentration and mobility. (b) Although the presence of some residual defects (mainly split interstitials) seems to accompany the appearance of the S related electrical activity, the level of residual damage in the S implanted samples is always less than that of the Ar control. (c) The electrical effects due to the implantation of S vanish upon annealing at temperatures in access of 800 °C. (d) No significant difference in the electrical properties between P and control Ar implantations are evident. It is concluded that a sulfur-defect related complex, which decomposes at T>800 °C, is responsible for the electrical effects in S implanted diamond. The presence of B contamination which has complicated the interpretation of experiments involving S doping during chemical vapor deposition diamond growth is excluded in the present work in which ion-implantation doping was employed.

High quality chemical vapor deposition diamond growth on iron and stainless steel substrates

Due to the catalytic effect and the rapid diffusion coefficients of carbon species into iron-based materials such as iron and 18-8 stainless steel [18% chrome (Cr) and 8% nickel (Ni)], it is very difficult to produce diamond grains on such substrates. However, diamond growth on iron-based materials is extremely important for mechanical and electrical applications, since these materials are widely used in industrial field and fundamental science. In our previous study, diamond nucleation and subsequent growth have been precisely controlled by the residence time of the source gas, which is an essential parameter. Here, we have carried out diamond growth on iron-based materials using the hot-filament chemical vapor deposition technique with varying residence times. At low residence times, diamond grains with practically useful growth rate are grown. The growth rate of diamond grains on stainless steel substrates was a factor of about 10 greater than that on a regular silicon substrate at optimum conditions. At optimized conditions, diamond growths with high crystalline quality on stainless steel substrates were confirmed by Raman spectroscopy and scanning electron microscopy. The full width of half maximums of the Raman peaks for diamonds grown in this study are comparable to the ones of natural diamonds.

Thermoluminescence Characteristics of a New Production of Chemical Vapour Deposition Diamond

The dosimetric properties are presented of a recent production of chemical vapour deposition diamond growth. Experimental data concerning the TL response as a function of dose, the energy response and fading behaviour are reported. Very preliminary results suggest that diamond can be used in TL mode as well as an activation detector.

Effects of temperature and pressure on CVD diamond growth from the C-H-O system

Isotherm, isopiestic, and vertical sections of the theoretical phase diagram for CVD (chemical vapor deposition) diamond growth are calculated. It is found that CVD diamond synthesis is restricted not only by the gas phase composition, but also by the temperature and pressure. The effects of temperature, pressure, and oxygen addition on the diamond growth region can be explained quantitatively. The calculation of the phase diagram provides a general prediction about suitable conditions for CVD diamond growth.

Influence of nanoscale surface curvature on prenucleation phenomena in chemical vapor deposition diamond growth

The problem of adsorption desorption of methyl radicals on a surface with nanoscale curvature is numerically studied for typical chemical vapor deposition diamond growth conditions. Surface profiles with concave nanoscale curvature lead to an increase in the energy of adsorption, which can enhance the nucleation of the new phase on the substrates. Moreover, the nanoscale curvature is even able to provoke a nucleation of the new phase on substrates which do not have an affinity for nucleation.

High-sensitivity absorption spectroscopy on a microwave plasma-assisted chemical vapour deposition diamond growth facility

High-sensitivity absorption spectroscopy using a multi-element detector was performed on a microwave plasma-assisted chemical vapour deposition (MPACVD) diamond growth facility. The absolute methyl radical column density and the line-of-sight average of the gas temperature were measured as functions of position in the discharge with input methane concentration 0 - 1%. The average absolute methyl radical density was nearly independent of position in the discharge and varied in the range as the input mole fraction varied in the range 0 - 1%. The gas temperature was measured using emission spectroscopy and was found to be independent of position throughout the discharge. An upper bound of was placed on the CH density, which gives an upper bound of 0.008 on the hydrogen dissociation ratio .

Interactions of hydrogen and methyl radicals with diamond C(111) studied by sum-frequency vibrational spectroscopy.

Methyl-radical and atomic hydrogen adsorption on C(111) have been studied by infrared-visible sum-frequency vibrational spectroscopy. Methyl iodide, di-tert-butyl-peroxide, and methane passing through a hot filament are used to produce methyl radicals (${\mathrm{CH}}_{3}$). Low-energy ${\mathrm{CH}}_{3}$ from pyrolytic dissociation at \ensuremath{\sim}800 \ifmmode^\circ\else\textdegree\fi{}C adsorb intact on the surface, but with surface annealing above 350 \ifmmode^\circ\else\textdegree\fi{}C, convert to tetrahedrally bonded CH. High-energy ${\mathrm{CH}}_{3}$ produced at \ensuremath{\sim}1800 \ifmmode^\circ\else\textdegree\fi{}C convert readily to CH upon adsorption. Co-dosing a high-temperature (\ensuremath{\sim}800 \ifmmode^\circ\else\textdegree\fi{}C) C(111) substrate with hydrogen and methane via a hot filament at \ensuremath{\sim}1800 \ifmmode^\circ\else\textdegree\fi{}C yields only the stable tetrahedrally-bonded CH-species on the surface. They appear to stabilize the diamond surface structure. The coverage is not full, leaving sites open for ${\mathrm{CH}}_{3}$ to adsorb and convert to CH as is necessary for chemical vapor deposition diamond growth. \textcopyright{} 1996 The American Physical Society.

The formation of atomic steps in chemical vapour deposition diamond growth

A mechanism for the formation of atomic steps in chemical vapour deposition diamond growth is proposed. First, a number of groups is adsorbed on the diamond (111) surface, each of which consists of three neighbouring methyl radicals, and there are small steric repulsions among these groups because of the large distances between them; second, the three CH 3 radicals in each of the groups are bound to form the step diamond structure via H abstraction of hydrogen atoms and CH 3 radical intermediates. The epitaxial growth possibly proceeds on addition of a certain species, such as C 2H 2 or CH 3 addition, until it encounters another step structure from epitaxial growth of another group of CH 3 radicals. Once the atomic steps are flattened, the process will be repeated again. This mechanism is supported by the results of first-principles discrete variational method calculations and is consistent with the conclusions reported in the literature.

Thermal chemical vapour deposition of homoepitaxial diamond: dependence of surface morphology and defect structure on substrate orientation

The crystallographic anisotropy in chemical vapour deposition diamond growth has been investigated by the homoepitaxial deposition of diamond layers on substrates of different orientations. The films were grown in a hot filament reactor. Diamond plates parallel to and 4° misoriented from {111}, {100} and {110}, as well as a hemispherically shaped diamond were used as substrates. Optical and scanning electron microscopy demonstrated that the surface morphology and thus the mechanism of diamond formation is strongly orientation dependent. Shallow growth hillocks, indicative of step growth, were found on the {111} and {100} faces. The plates slightly misoriented from these two low index directions are covered by surface dendrites, bunch patterns and macrosteps. The other orientations, including {110}, are rough and show features characteristics of S or K faces. The F character of {100} suggests the occurence of (2 × 1) surface reconstruction during crystal growth. Cathodoluminescence topography and spectroscopy proved that the crystallographic orientation of the growing surface also plays a main role in the formation of point defects.