Step growth in single crystal diamond grown by microwave plasma chemical vapor deposition

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

Diamond nitrogen vacancy (NV) color centers have good stability at room temperature and long electron spin coherence time, and can be manipulated by lasers and microwaves, thereby becoming the most promising structure in the field of quantum detection. Within a certain range, the higher the concentration of NV color centers, the higher the sensitivity of detecting physical quantities is. Therefore, it is necessary to dope sufficient nitrogen atoms into diamond single crystals to form high-concentration NV color centers. In this study, diamond single crystals with different nitrogen content are prepared by microwave plasma chemical vapor deposition (MPCVD) to construct high-concentration NV color centers. By doping different amounts of nitrogen atoms into the precursor gas, many problems encountered during long-time growth of diamond single crystals under high nitrogen conditions are solved. Diamond single crystals with nitrogen content of about 0.205, 5, 8, 11, 15, 36, and 54 ppm (1 ppm = 10<sup>–6</sup>) are prepared. As the nitrogen content increases, the width of the step flow on the surface of the diamond single crystal gradually widens, eventually the step flow gradually disappears and the surface becomes smooth. Under the experimental conditions in this study, it is preliminarily determined that the average ratio of the nitrogen content in the precursor gas to the nitrogen atom content introduced into the diamond single crystal lattice is about 11. Fourier transform infrared spectroscopy shows that as the nitrogen content inside the CVD diamond single crystal increases, the density of vacancy defects also increases. Therefore, the color of CVD high nitrogen diamond single crystals ranges from light brown to brownish black. Compared with HPHT diamond single crystal, the CVD high nitrogen diamond single crystal has a weak intensity of absorption peak at 1130 cm<sup>–1</sup> and no absorption peak at 1280 cm<sup>–1</sup>. Three obvious nitrogen-related absorption peaks at 1371, 1353, and 1332 cm<sup>–1</sup> of the CVD diamond single crystal are displayed. Nitrogen atoms mainly exist in the form of aggregated nitrogen and single substitutional N<sup>+</sup> in diamond single crystals, rather than in the form of C-defect. The PL spectrum results show that defects such as vacancies inside the diamond single crystal with nitrogen content of 54 ppm are significantly increased after electron irradiation, leading to a remarkable increase in the concentration of NV color centers. The magnetic detection performance of the NV color center material after irradiation is verified, and the fluorescence intensity is uniformly distributed in the sample surface. The diamond single crystal with nitrogen content of 54 ppm has good microwave spin manipulation, and its longitudinal relaxation time is about 3.37 ms.

Homoepitaxial growth of single crystal diamond by microwave plasma chemical vapor deposition

Homoepitaxial lateral growth of single-crystal diamond with eliminating PCD rim and enlarging surface area

We report the simultaneous enlarged growth of seven single crystal diamond (SCD) plates free from polycrystalline diamond (PCD) rim by using a microwave plasma chemical vapor deposition (MPCVD) system. Optical microscope and atomic force microscope (AFM) show the typical step-bunching SCD morphology at the center, edge, and corner of the samples. The most aggressively expanding sample shows a top surface area three times of that of the substrate. The effective surface expanding is attributed to the utilization of the diamond substrates with (001) side surfaces, the spacial isolation of them to allow the sample surface expanding, and the adoption of the reported pocket holder. Nearly constant temperature of the diamond surfaces is maintained during growth by only decreasing the sample height, and thus all the other growth parameters can be kept unchanged to achieve high quality SCDs. The SCDs have little stress as shown by the Raman spectra. The full width at half maximum (FWHM) data of both the Raman characteristic peak and (004) x-ray rocking curve of the samples are at the same level as those of the standard CVD SCD from Element Six Ltd. The nonuniformity of the sample thickness or growth rate is observed, and photoluminescence spectra show that the nitrogen impurity increases with increasing growth rate. It is found that the reduction of the methane ratio in the sources gas flow from 5% to 3% leads to decrease of the vertical growth rate and increase of the lateral growth rate. This is beneficial to expand the top surface and improve the thickness uniformity of the samples. At last, the convenience of the growth method transferring to massive production has also been demonstrated by the successful simultaneous enlarged growth of 14 SCD samples.

Comparative study of homoepitaxial single crystal diamond growth at continuous and pulsed mode of MPACVD reactor operation

A growth of single crystal diamond (SCD) microchannels on HPHT diamond substrate has been carried out successfully by a simple and novel method. Firstly, aluminum film was patterned on SCD diamond substrate surface by magnetron sputtering, photolithography and dry etching techniques. Secondly, the aluminum patterns were transferred onto diamond substrate via inductively coupled plasma etching to form grooves on diamond surface. Finally, microchannels were achieved by epitaxial lateral overgrowth of SCD on the surface of prepared substrate by microwave plasma chemical vapor deposition system. After that, fluorescent liquid was introduced to check hollowness of the microchannels. This work provides a simple and time saving method to fabricate SCD microchannels for microfluidic system, which offers a great potential for hard environment applications.

Substrate temperature and methane concentration in Hydrogen (H2) gas mixture is the main source for increasing the growth rate, nucleation and grain size of a synthetic diamond. The downside of such an approach is reduced quality. By increasing the chamber pressure, although the quality can be improved, however, it leads to a decrease in the crystal growth rate. Thin diamond films were deposited under hydrogen (H2) and methane (CH4) gas mixture using microwave plasma chemical vapor deposition (MPCVD) technique. The effect of methane concentration (1%–5%), growth temperature, and pressure on the nucleation of diamond thin films on diamond substrates was investigated. The growth temperature and pressure were maintained in the range of 925 °C–950 °C and 72–75 Torr, respectively. Single crystal diamond (SCD) thin films have been prepared on diamond substrates, which play an important role in the application of the diamond detectors. Different dimensions of films were obtained on diamond substrates with different thicknesses such as 209.17 μm, 401.73 μm, and 995.03 μm for the sample with 1%, 2% and 5% of methane concentration respectively. The roughness, as well as growth rate of these films, were also investigated and were found to be 4.23 nm and 5.02 μ h−1, respectively for 5% methane by optimizing the substrate temperature at 950 °C. Different characterization techniques were used to study the structural, morphological, and compositional properties of the deposited diamond films which confirmed the crystallographic order of the developed diamond film on the diamond substrates.

Homoepitaxial single crystal diamond growth at different gas pressures and MPACVD reactor configurations

Growth of single-crystal diamond by microwave plasma CVD with high precursor utilization using cyclic gas injection and control of carbonaceous species content with optical emission spectroscopy

The effects of self-assembling off-angles on the homoepitaxial lateral outward growth of single-crystal diamond

The epitaxial lateral growth of single-crystal diamond (SCD) using a plate-to-plate microwave plasma chemical vapor deposition (MPCVD) reactor under high pressure is investigated. The radicals’ distribution in H2/CH4 plasma as a function of pressure was locally detected by optical emission spectroscopy (OES). Raman spectroscopy and optical microscope were employed to analyze the properties of SCD deposited in different pressure. The OES results show that radicals’ distribution along the substrate direction is symmetrical under 20 kPa pressure. The symmetrical distribution of radicals at 20 kPa is in favor of epitaxial lateral growth SCD around the seed and without polycrystalline diamond (PCD) rim. When the pressure is increased to 21.5 kPa, the optical emission spectra center of plasma shifts close to the microwave reflector where is far away from the microwave source. The contact state between the diamond seed and the plasma is deteriorated and the PCD rim occurs in the plasma uncovered area. While the epitaxial lateral growth pattern occurs in the plasma covered area and the lateral growth rate of this region improves with the increase of pressure. A higher growth rate does not result in good quality; meanwhile, the diamond growth step spacing and direction become inconsistent in the transition zone as a function of pressure increasing. Finally, the overall effective lateral expansion area does not increase with the improvement of pressure. Therefore, the uniform and symmetrical distributed plasma is more conducive to the epitaxial lateral growth of SCD, and the effective expansion growth SCD can be realized at 20 kPa.

This thesis focuses on the study of growth of homoepitaxial diamond film with embedded gold nanoparticles (AuNPs) by microwave plasma chemical vapor deposition (MPCVD). The first part of this thesis deals with the preparation of gold nanoparticles on diamond (111) single crystal substrate. The effect of various plasma conditions on the distribution of gold nanoparticles on diamond (111) was explored by varying power and methane concentration in plasma. In the second part, the well fabricated AuNPs/ diamond (111) was used as the substrate for further growth of oriented diamonds by MPCVD. Finally, the results of multi-step growth of epitaxial diamond film with embedded AuNPs are presented. The gold film was deposited on ~ 2 mm sized diamond (111) single crystal substrate by electron beam evaporation. The as-deposited Au on diamond was then annealed in vacuum. The higher temperature results in more uniform distribution of AuNPs on diamond substrate. The distribution of AuNPs on diamond is also affected with the thickness of the deposited gold layer and the MPCVD conditions for homoepitaxial diamond film including hydrogen/methane concentration, microwave . The morphology and roughness after the plasma treatment were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that the as-deposited diamond on 20nm thickness of gold layer has more uniform distribution in 0.5% methane plasma at microwave power of 800 W. In the diamond growth process, oriented diamond films were deposited on diamond substrate covered with gold by the same process parameters including mixed ratio of CH4 and H2, pressure, power, etc. Comparing with the diamond film in the various time, we can set up the growth model of diamond characterized by AFM and X-ray diffraction (XRD). At the beginning, the growth of diamond islands appears between AuNPs, followed by lateral overgrowth with coalenscence when diamond islands covers the AuNPs. From cross-sectional transmission electron microscopy (TEM) observation, a graphite layer exists at the AuNPs/diamond interface. Secondly, diamond films obtained by step direct growth on diamond seed and by multi-layer growth of gold were characterized by optical microscopy (OM) and Raman spectroscopy. The results show that cracks appear after diamond film deposition for eight hours, while the film processed with multi- layer growth of gold shows no cracks. Raman spectra show the peak in the range of 1326-1332 cm-1, suggesting that diamond films are in tensile stress. XRD and reciprocal space mapping (RSM) were used to evaluate the effect of embedded AuNPs on cracking by determination of the d-spacings of diamond and embedded gold. The results show the out-of-plane and in-plane d-spacings of diamond become larger than the bulk values, whereas gold’s d-spacings become smaller. TEM reveals the distribution of embedded AuNPs and the microstructure of epitaxial lateral growth of diamond with formation of stacking faults and threading dislocations after the coalescence of islands in the step growth. After 4 step growth, the dislocation density can be reduced to 1.41x108 cm-2. It implies the embedded gold particles may restrain the formation of the cracks on diamond.

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.

Introduction Diamond, owing to its exceptional impact resistance, high thermal conductivity, broad-spectrum optical transparency, elevated breakdown field strength, and superior carrier mobility, finds widespread application in diverse fields such as high-power laser windows, efficient heat spreader, and high-performance semiconductor devices. Experimental 1. Heteroepitaxial Growth of Polycrystalline Diamond on Si, SiC, and Mo Substrates:In this part, substrates employed include double-side polished 4H-polytype SiC, (100) single-side polished single-crystal Si wafers, and Mo substrates. Ultrasonic grinding of substrates using diamond powder ethanol suspension to promote the dispersion of nucleation seeds, followed by sequential ultrasonic cleaning in acetone, ethanol, and deionized water.Subsequently, MPCVD was used for diamond growth, using hydrogen, methane, oxygen, and a mixture of hydrogen and nitrogen as reaction gases. Using different processes to produce efficient heat sinks and high-power laser windows. 2. Homoepitaxial Growth of Single-Crystal Diamond on Diamond Substrates:In the homoepitaxial growth process, (100) double-side polished single-crystal diamond substrates are utilized. No need for ultrasonic grinding steps, cleaning steps are the same as above. Then use MPCVD for homogeneous epitaxial growth of single-crystal diamond. 3. Investigation of Graphitized Surface Devices on Diamond:This study also investigated the graphitization devices on diamond surfaces. A high-temperature metal-catalyzed method is employed to promote surface graphitization of diamond. Firstly, polish and clean the diamond. Subsequently, a 300 nm thick nickel layer is deposited on the diamond surface. Rapid thermal annealing is then performed at 1300°C to form a highly conductive graphite layer. This process successfully prepares capacitor samples with a graphite-diamond-graphite three-layer structure. Results and Discussion 1. High-Power Laser Window Plates:The fabricated laser window plates utilize Si, SiC and Mo substrates, employing an ultra-low nitrogen growth process with a growth rate of approximately 3.7 µm/h. After double-sided polishing, the thickness reaches 1 mm. At room temperature, the transmittance at 10.6 µm wavelength approaches the theoretical maximum, reaching 67.9%. The overall thermal conductivity exceeds 1950 W/mK, approximating that of single-crystal diamond.Raman spectroscopy and XRD results indicate that the primary component is polycrystalline diamond with a (110) crystallographic orientation. Laser testing results demonstrate that these window plates possess a high laser-induced damage threshold with a peak energy of 60 J/cm2 and a peak power of 12 MW/mm2, capable of withstanding high-power CO2 laser output. 2. Heat Spreader:This study involves depositing diamond on Si and SiC substrates, forming diamond-based composite materials. This significantly improves the heat dissipation efficiency of the devices, bringing their performance closer to theoretical limits. The deposition process employs a low-nitrogen technique to balance growth rate and defect density, achieving a growth rate of approximately 5 µm/h.Raman spectroscopy and XRD results indicate that the primary component is polycrystalline diamond with a (110) crystallographic orientation. Although the increased nitrogen content results in lower optical transmittance compared to optical window plates, the grain size can be increased from 124 nm to 22 μm through production process adjustments, thereby enhancing thermal conductivity.Test results demonstrate that the thermal conductivity of the Si-diamond composite material reaches 450 W/mK,3 times that of single-crystal Si. The SiC-diamond composite material achieves a thermal conductivity of 500 W/mK,3.5 times that of SiC. 3. Single-Crystal Diamond:The transmittance and thermal conductivity of single-crystal diamond grown by homoepitaxial growth are superior to those of polycrystalline diamond. However, limitations in size and growth conditions restrict its large-scale application in heat spreaders and optical windows. Single-crystal diamond is more suitable for manufacturing semiconductor devices such as diamond capacitors, Schottky diodes, and hydrogen-terminated MOSFETs.The author has conducted research on doping of single-crystal diamond. Characterization through Raman spectroscopy, XRD, and TEM confirms that the primary component is single-crystal diamond with a (100) crystallographic orientation. The dislocation density is below 103/cm2, meeting the stringent requirements for semiconductor devices. 4. Graphite-Diamond-Graphite Capacitors:Utilizing prepared diamond, graphite-diamond-graphite capacitors were fabricated. Measurements using a semiconductor parameter analyzer revealed a high capacitance value of 4 nF. TCAD simulation indicated a breakdown voltage as high as 1100 V. This research explores a novel method for diamond capacitor fabrication. Conclusions Diamond heteroepitaxial grown on Si, SiC, and Mo substrates has prepared high-power laser windows with 67.9% optical transmittance at 10.6 μm wavelength, and composite materials with thermal conductivity enhanced to 3-3.5 times that of the original materials. Homoepitaxially grown diamond on single-crystal diamond substrates exhibits a dislocation density below 10³/cm², meeting the requirements for semiconductor device substrates. Furthermore, this research has developed a novel diamond capacitor fabrication technique, yielding capacitors with a capacitance of 4 nF and a breakdown voltage of 1100 V.