Single Crystal Diamond Layers Research Articles

Effect of step-flow modulation on the large-size single crystal diamond through mosaic growth

In this paper, large-size single crystal diamond is grown by microwave plasma chemical vapor deposition using mosaic technique. The effects of the step-flow modulation on the surface morphology and crystal quality of epitaxial single crystal diamond layer are systematically investigated. It demonstrates that the two adjacent crystals can be merged into a single crystal layer with good surface morphology and uniform quality when their step-flow orientations are similar. Otherwise, over-lap is observed because of the overgrowth from one seed to another, resulting in stress concentration and a large number of crystalline defects at the mosaic boundaries. Finally, we demonstrate that the step-flow modulation method facilitates the mosaic growth of inch-scale single-crystal diamond with 10 CVD seeds arranged in a T-shape.

Comparison of heteroepitaxial diamond nucleation and growth on roughened and flat Ir/SrTiO3 substrates

Heteroepitaxial diamond deposition on iridium substrates allows production of single crystal diamond layers on large area that is difficult to achieve with homoepitaxy. Critically important is the first stage of the process when diamond nucleates on Ir upon biasing (a voltage applied to the substrate). Here, we compared the heteroepitaxial nucleation and successive growth of diamond thin films in a microwave plasma CVD reactor on Ir/SrTiO3 substrates with different surfaces modified by bias voltage. The roughened surface consists of furrows and ridges while the flat surface is a little wrinkled. The film morphology, crystal quality and stress are characterized with SEM, AFM, TEM, X-ray diffraction and Raman spectroscopy. It is found that the film on the roughened Ir surface has a lower roughness, smaller mosaic spread, but a larger residual stress than the film deposited on the flat Ir surface, which mainly originates from the difference in the domain density. By comparing diamond (111) lattice spacings of different positions from the Ir-diamond interface, it is inferred that diamond nucleation could occur at the furrows and then overgrow the ridges for Ir-roughened sample while diamond may nucleate at the wrinkle and flat regions for Ir-flat sample. These finding are helpful in understanding of details of diamond film heteroepitaxy, and in searching the ways to improve their crystallinity.

Surface Morphology and Microstructure Evolution of Single Crystal Diamond during Different Homoepitaxial Growth Stages.

Homoepitaxial growth of step-flow single crystal diamond was performed by microwave plasma chemical vapor deposition system on high-pressure high-temperature diamond substrate. A coarse surface morphology with isolated particles was firstly deposited on diamond substrate as an interlayer under hillock growth model. Then, the growth model was changed to step-flow growth model for growing step-flow single crystal diamond layer on this hillock interlayer. Furthermore, the surface morphology evolution, cross-section and surface microstructure, and crystal quality of grown diamond were evaluated by scanning electron microscopy, high-resolution transmission electron microcopy, and Raman and photoluminescence spectroscopy. It was found that the surface morphology varied with deposition time under step-flow growth parameters. The cross-section topography exhibited obvious inhomogeneity in crystal structure. Additionally, the diamond growth mechanism from the microscopic point of view was revealed to illustrate the morphological and structural evolution.

Impact of CVD-synthesis parameters and film thickness on growth rate of single-crystal diamond

The widespread use of CVD-reactors of various constructions and the influence of many factors on the formation of energy-saturated reaction zone has led to the fact of significant difference of technological parameters optimal for each reactor even of one brand. An economically important parameter, in addition to the quality of the obtained single-crystal diamond layer, is the growth rate, which depends on many factors: the flow rate and chemical composition of gases, pressure in the reaction chamber, substrate temperature, the shape of the formed plasma cloud, dimensions and shape of molybdenum substrate holders and et al. This work is devoted to the experimental determination of the single-crystal CVD-diamonds growth rate across various synthesis conditions on Ardis 300. In research, we shown the effect of the thickness of the synthesized diamond layer on the rate of formation of subsequent diamond layers, which is associated with a change in the degree of misorientation between the crystallographic plane (100) and direction [100]. Also, this can be associated with an increase in the roughness of the growing surface, leading to an increase in the specific number of active centers thermodynamically favorable for carbon deposition during the formation of the crystal structure of diamond.

Impact of methane concentration on surface morphology and boron incorporation of heavily boron-doped single crystal diamond layers

The methane concentration dependence of the plasma gas phase on surface morphology and boron incorporation in single crystal, boron-doped diamond deposition is experimentally and computationally investigated. Starting at 1%, an increase of the methane concentration results in an observable increase of the B-doping level up to 1.7×1021 cm−3, while the hole Hall carrier mobility decreases to 0.7±0.2 cm2 V−1 s−1. For B-doped SCD films grown at 1%, 2%, and 3% [CH4]/[H2], the electrical conductivity and mobility show no temperature-dependent behavior due to the metallic-like conduction mechanism occurring beyond the Mott transition. First principles calculations are used to investigate the origin of the increased boron incorporation. While the increased formation of growth centers directly related to the methane concentration does not significantly change the adsorption energy of boron at nearby sites, they dramatically increase the formation of missing H defects acting as preferential boron incorporation sites, indirectly increasing the boron incorporation. This not only indicates that the optimized methane concentration possesses a large potential for controlling the boron concentration levels in the diamond, but also enables optimization of the growth morphology. The calculations provide a route to understand impurity incorporation in diamond on a general level, of great importance for color center formation.

Liftoff of single crystal diamond by epitaxial lateral overgrowth using SiO2 masks

We describe a method that allows an easy separation of a single crystal diamond layer grown by homoepitaxy in a chemical vapour deposition (CVD) process from the growth substrate. In a first step a thin SiO2 layer is deposited on top of the seed crystal. This layer is patterned by photolithography and reactive ion etching (RIE) to obtain a mask with open windows and covered areas. In an epitaxial lateral overgrowth (ELO) process diamond is grown homoepitaxially through the free window areas and laterally across the covered areas until the mask is completely covered by diamond. During cool down from deposition temperature tensile stress σzz perpendicular to the growth surface is formed in the diamond bridges grown in the window areas. The absolute value of the stress depends on growth temperature, difference in coefficients of thermal expansion (CTE) between diamond and the specific mask material and finally on the fill factor (FF). The stress amplitude can reach more than +2 GPa and stress intensity factors in the range of typical fracture toughness values reported for single crystal diamond. Our experiments demonstrate that an immediate crack formation can be achieved which facilitates an easy separation between the CVD grown diamond layer and the seed crystal. The described concept develops its highest potential with increasing lateral dimensions of the seed wafers.

Enhancing diamond NV center density in HPHT substrate and epitaxy lateral overgrowth layer by tungsten pattern

The nitrogen vacancy (NV) center distribution in epitaxial lateral overgrowth (ELO) single crystal diamond layer grown on tungsten patterned HPHT substrate by microwave plasma chemical vapor deposition (CVD) system has been investigated. It has been found that in ELO diamond layer densities of NV0 and NV− center above the tungsten metal are enhanced. Meanwhile, in patterned high-pressure and high-temperature (HPHT) substrate the density of NV− center beneath the tungsten metal is much higher than that of NV0. The HPHT substrate does not contain NV centers before CVD growth, and there is almost no NV center in the region without tungsten metal after growth.

Surface conductivity enhancement of H-terminated diamond based on the purified epitaxial diamond layer

Diamond-based semiconductor with high electrical conductivity is a key point in diamond device development. In this paper, a thin single crystal diamond layer of high quality was epitaxially grown on a commercial tool-grade diamond seed by incorporating active O atoms from the typical growth environment. Subsequently, the H-termination density was enhanced on the diamond surface by exposure to the pure hydrogen plasma, and the surface conductivity of H-terminated diamond was analyzed in detail. The thin epitaxial layers on the high-pressure high-temperature diamond seeds show lower resistance than the ones on the chemical vapor deposition diamond seeds, which could be comparable with the lowest values reported. After the thin diamond layers were grown with and without addition of O2, the carrier mobility in the conductive channel increased to almost 80 cm2 V−1 s−1 under O2 contained condition, much higher than those without O2 incorporation. The ionization scattering is dominant to the carrier mobility compared with the surface scattering. The higher carrier mobility is attributed to the lower impurity density in the epitaxial layer, which is because the active O atoms could purify the epitaxial layer by removing or reducing Si- and N-related impurities.

Process and apparatus for hydroprocessing and cracking hydrocarbons

Vertical structure metal-insulator-p-type diamond Schottky barrier diodes (SBDs) with different thickness drift layers have been fabricated. Un-doped single crystal diamond layers were grown on HPHT boron doped diamond substrates as the drift layers. Then, Mo/Ni/Au was deposited on the drift layer as Schottky electrode and Ti/Au was deposited on the back side of diamond substrate as ohmic electrode. The ideality factor and Schottky barrier height of diode were evaluated from current-voltage curve. The minimum reverse current density of SBD could be as low as 100 pA/cm2 at 10 V and the maximum forward current density is 7570 A/cm2 at − 10 V. The rectification ratio and the breakdown electric field reached 12 orders and 4.2 MV/cm, respectively.

Express in situ measurement of epitaxial CVD diamond film growth kinetics

We used a low-coherence interferometry for precise continuous in situ measurements of thickness and growth rate of epitaxial single crystal diamond layers in microwave plasma CVD in H2-CH4 gas mixtures in a broad range of substrate temperatures Ts (750–1150°C) and CH4 concentrations (1–13%). Rich growth kinetics is collected in a single experiment by depositing about 60 layers on one (100) Ib HPHT diamond substrate in different regimes (the substrate temperature was controlled by the microwave power) at fixed pressure P=130Torr, without the plasma switch-off. The growth rate is found to follow Arrhenius dependence with activation energy Ea=11.1±1.0kcal/mol. By appropriate choice of the substrate temperature the growth rate can be significantly enhanced. The growth rate as high as 82μm/h is achieved by optimizing the temperature and gas composition. At low CH4 content (1%) growth competes with etching by atomic hydrogen, the etching dominating at high Ts (>1000°C in the present conditions). The etching rate in pure H2 plasma was measured and activation energy Ea=9.8±0.8kcal/mol was deduced. Gas temperature Tg in the plasma core evaluated from optical emission spectra for dimer C2 (Swan band), was found to be either constant or slightly and monotonically increasing with absorbed power, whereas the absorbed microwave power density shows a decreasing, although slight, trend. This suggests the temperature depended surface reactions to play a major role in the diamond growth kinetics under variable microwave power. Raman mapping of cross-section of the produced multilayered sample confirmed high quality of diamond structure over all the deposition regimes explored.

Diamond MIP structure Schottky diode with different drift layer thickness

Vertical structure metal-insulator-p-type diamond Schottky barrier diodes (SBDs) with different thickness drift layers have been fabricated. Un-doped single crystal diamond layers were grown on HPHT boron doped diamond substrates as the drift layers. Then, Mo/Ni/Au was deposited on the drift layer as Schottky electrode and Ti/Au was deposited on the back side of diamond substrate as ohmic electrode. The ideality factor and Schottky barrier height of diode were evaluated from current-voltage curve. The minimum reverse current density of SBD could be as low as 100pA/cm2 at 10V and the maximum forward current density is 7570A/cm2 at −10V. The rectification ratio and the breakdown electric field reached 12 orders and 4.2MV/cm, respectively.

Fabrication of UV Photodetector on TiO2/Diamond Film

The properties of ultraviolet (UV) photodetector fabricated on TiO2/diamond film were investigated. Single crystal diamond layer was grown on high-pressure-high-temperature Ib-type diamond substrate by microwave plasma chemical vapor deposition method, upon which TiO2 film was prepared directly using radio frequency magnetron sputtering technique in Ar and O2 mixing atmosphere. Tungsten was used as electrode material to fabricate metal-semiconductor-metal UV photodetector. The dark current is measured to be 1.12 pA at 30 V. The photo response of the device displays an obvious selectivity between UV and visible light, and the UV-to-visible rejection ratio can reach 2 orders of magnitude. Compared with that directly on diamond film, photodetector on TiO2/diamond film shows higher responsivity.

Photoluminescence of SiV centers in single crystal CVD diamond in situ doped with Si from silane

Homoepitaxial single crystal diamond layers with bright photoluminescence (PL) of silicon‐vacancy (SiV) color centers at 738 nm wavelength have been grown on (100) diamond substrates by a microwave plasma CVD using a controlled Si doping via adding silane to CH4H2 reaction gas mixture in the course of the deposition process. In the range of the silane concentrations SiH4/CH4 explored, from 0 to 2.4%, the SiV PL intensity shows a nonmonotonic behavior with silane addition, with a maximum at 0.6%SiH4/CH4, and a rapid PL quenching at higher Si doping. The maximum SiV concentration of ≈450 ppb in the samples has been determined from optical absorption spectra. It is found that the SiV PL intensity can strongly, an order of magnitude, increase within non‐epitaxial inclusions in single crystal diamond film.

High-rate homoepitaxial growth of CVD single crystal diamond by dc arc plasma jet at blow-down (open cycle) mode

Abstract Growth and applications of large size high quality single crystal diamond is one of the most significant progresses in the field of CVD diamond film research ever made in the past 15 years. However, up to now most of the works were done by microwave plasma CVD operating at high pressures. In the present investigation it is demonstrated that relatively high quality single crystal diamond layer with the FWHM of the diamond Raman peak of less than 2 cm− 1 and the FWHM of the diamond (400) reflection X-ray Rocking Curve of 0.028° can be obtained by the 20 kW dc arc plasma jet operating at blow down (open cycle) mode at a growth rate as high as 36 μm/h. The reason why dc arc plasma jet is also suitable for high quality epitaxial growth of single crystal diamond is that very high concentration of atomic hydrogen can be easily provided by the extremely high gas temperature due to the arc discharging. Detailed results on the effects of the ratio of H2/Ar, the distance between the substrate to the anode nozzle of the arc plasma torch, the concentration of methane, and the substrate temperature on the growth of single crystal diamond are presented, and discussed comprehensively, and compared to that with the MWCVD, and with our previous work on the 30 kW dc arc plasma jet operating at arc root rotation and gas recycling mode.

Growth of single-crystal diamonds in microwave plasma

A microwave plasma (2.45 GHz) was used for depositing single crystal diamond layers at the deposition rate up to 40 μm/h in hydrogen-methane mixtures on the substrates from natural and synthetic diamond with the (100) deposition surface and with the size up to 5 × 5 mm. The structure and the defect-impurity composition of the fabricated single crystals with the thickness up to 600 μm have been investigated using Raman spectroscopy, photoluminescence spectroscopy, cathode luminescence spectroscopy, and electron and optical microscopy. A high quality and purity of the diamond layers deposited from a plasma was confirmed.

Optical and Spin Coherence Properties of Nitrogen-Vacancy Centers Placed in a 100 nm Thick Isotopically Purified Diamond Layer

We have studied optical and spin properties of near-surface nitrogen-vacancy (NV) centers incorporated during chemical vapor phase growth of isotopically purified (12)C single-crystal diamond layers. The spectral diffusion-limited line width of zero-phonon luminescence from the NV centers is 1.2 ± 0.5 GHz, a considerable improvement over that of NV centers formed by ion implantation and annealing. Enhanced spin dephasing times (T(2)* ≈ 90 μs, T(2) ≈ 1.7 ms) due to the reduction of (13)C nuclear spins persist even for NV centers placed within 100 nm of the surface.

Characterization of single-crystal diamond grown from the vapor phase on substrates of natural diamond

The results of studies of single-crystal diamond layers with orientation (100) grown on substrates of IIa-type natural diamond by chemical-vapor deposition and of semiconductor diamond obtained subsequently by doping by implantation of boron ions are reported. Optimal conditions of postimplantation annealing of diamond that provide the hole mobility of 1150 cm2 V−1 s−1 (the highest mobility obtained so far for semiconductor diamond after ion implantation) are given.

Arsenic-Doped n-Type Diamond Grown by Microwave-Assisted Plasma Chemical Vapor Deposition

We grew n-type arsenic (As)-doped single-crystal diamond layers using tertiarybutylarsine as an As source. The n-type conduction of the As-doped layers was confirmed both in Hall measurements and from the current–voltage characteristics of the diodes. In the As-doped layers, electron concentration increased with As concentration in the layers. The ionization energy of the As donor decreased from 1.6 to 0.7 eV with As concentration from 1×1017 to 9×1019 cm-3. A diamond p–n junction diode with an n-type As-doped layer exhibited a rectification ratio of ∼1000 at ±10 V at room temperature.

Surface stress measurement with interference microscopy of thick homoepitaxial single-crystal diamond layers

In this article, we present a study of surface stress measurements of a thick single-crystal diamond (SCD) layer (110 μm) deposited onto a high-temperature high-pressure (HTHP) Ib substrate. The measurement is based on observations of the deformation of the backside of the HTHP substrate due to internal stress that varies as the thickness of the SCD layer is modified by ion-beam etching. The deformation is obtained from the height-distribution analysis of interference microscopy (IM) observation. The results show that the tensile surface stress σ increases linearly with SCD-layer thickness with t f according to σ = 0.065t f MPa/μm. The tensile surface stress may be attributed to the intrinsic stress that originates from the lattice mismatch between the CVD-diamond layer and the HTHP-Ib substrate. The increased internal stress is a principle cause of crack formation of the crystal.

Doping of single crystalline diamond with nickel

AbstractNickel doped single crystal diamond layers were grown by microwave‐plasma enhanced chemical vapour deposition. Optical emission spectroscopy (OES) utilised during growth proved that the organometallic compound nickelocene is an applicable nickel source. It was possible to produce stable and adjustable nickel OES signals during growth by altering the flux of the nickelocene carrier gas. The successful incorporation of nickel into the diamond layers was verified by secondary ion mass spectrometry. Cathodoluminescence (CL) was applied to reveal optically active defects related to nickel. The signature of substitutionally incorporated nickel, namely the nickel related 1.4 eV centre, as well as the 2.369 and 1.563 eV centres were observed in CL. The latter is supposed to be a single‐photon emitter on the basis of a nickel–nitrogen defect centre.