Single Crystal Diamond Films Research Articles

Application of dual radio frequency inductive coupled plasma into CVD diamond growth

Diamond films have been deposited by a tandem type of radio frequency inductive coupled plasma jet source with the maximum deposition time of 150 h. The morphology, impurity and crystal structure of the deposited films were characterized. By controlling the feed gas composition, nano- and micro-crystal diamond films were deposited on silicon substrates without any metal impurity detected, and the single crystal diamond film was deposited on a diamond substrate with regular crystal lattice structure. Plasma diagnosed by optical emission spectra revealed that this plasma jet source possessed of the high values of the electron temperature (averaged at 2.2eV) and the plasma density (averaged at 4.0 × 1016/cm3), as well as the stable plasma composition fitting for the diamond growth.

New Cluster Secondary Ions for Quantitative Analysis of the Concentration of Boron Atoms in Diamond by Time-of-Flight Secondary-Ion Mass Spectrometry

A new approach to quantitative analysis of the concentration of boron atoms in diamond using secondary- ion mass spectrometers with time-of-flight mass analyzers is proposed. Along with the known boron-containing lines (B, BC, BC2), many lines related to cluster secondary ions BC N have been found in the mass spectrum; their intensity increases by one or two orders of magnitude when Bi3 probe ions are used. Lines BC4, BC6, BC2, and BC8 have the highest intensity (in the descending order); when they are summed, the sensitivity increases by an order of magnitude in comparison with the known mode of detecting BC2. The parameters of the boron δ-layer in single-crystal diamond films grown under optimal conditions have been measured to be unprecedented: the δ-layer width is about 2 nm, and the concentration is 6.4 × 1020 cm–3 (the boron concentrations for doped and undoped diamonds differ by four orders of magnitude).

Новые кластерные вторичные ионы для количественного анализа концентрации атомов бора в алмазе методом времяпролетной вторично-ионной масс-спектрометрии

AbstractA new approach to quantitative analysis of the concentration of boron atoms in diamond using secondary- ion mass spectrometers with time-of-flight mass analyzers is proposed. Along with the known boron-containing lines (B, BC, BC_2), many lines related to cluster secondary ions BC_ N have been found in the mass spectrum; their intensity increases by one or two orders of magnitude when Bi_3 probe ions are used. Lines BC_4, BC_6, BC_2, and BC_8 have the highest intensity (in the descending order); when they are summed, the sensitivity increases by an order of magnitude in comparison with the known mode of detecting BC_2. The parameters of the boron δ-layer in single-crystal diamond films grown under optimal conditions have been measured to be unprecedented: the δ-layer width is about 2 nm, and the concentration is 6.4 × 10^20 cm^–3 (the boron concentrations for doped and undoped diamonds differ by four orders of magnitude).

Coherent Phonon-Mode Excitation in Submicron Single-Crystal Diamond Films with a Graphitized Layer Built-In

We report the first experimental observation of high-efficient phonon-mode coherent excitation using stimulated low-frequency Raman scattering (SLFRS) in submicron diamond{graphite{diamond heterostructure films with an ion-beam-induced graphitized layer. We show that the SLFRS process in submicron diamond heterostructures has a frequency shift in the gigahertz range and estimate experimentally the SLFRS conversion efficiency and threshold.

Molecular dynamics simulations for responses of nanotwinned diamond films under nanoindentation

We performed molecular dynamics (MD) simulations for the responses of single crystal (SC) and nanotwinned (nt) diamond films under nanoindentation, respectively, aimed to uncover the effects of twin boundary (TB) and twin thickness (δ) on hardness (H) and the corresponding deformation mechanisms. We found the Hall-Petch type relationship between H and δ. We also found that the inelastic deformation of SC-diamond under indentation could mainly be attributed to the nucleation and propagation of 〈110〉{111} dislocation loops. It showed that dislocation blockage and pile up at the TBs may induce additional hardening of the nt-diamond, while the softening of the material could be attributed to: (i) the formation and movement of the dislocation loops parallel with the surface, and (ii) the breakage of TBs, which may serve as new sites for dislocations nucleation.

Epitaxial Growth of Diamond by In-Liquid Plasma CVD Method

Currently, novel method to synthesize diamond film on material substrate called as in-liquid microwave plasma CVD (IL-MPCVD) has been achieved. It has been studied and improved in addition expected as new method instead of conventional gas phase microwave plasma CVD (MPCVD). The purpose of this study is to synthesize single crystal diamond using IL-MPCVD in high speed deposition. The experimental conditions, methanol was poured in to the reactor. Each of diamond particles (100) and (111) was embedded on the stainless steel substrates (SUS632J2). It was mounted to the substrate holder of in-liquid plasma equipment and installed on the top cover. The distance between the tip of the electrode and the substrate was kept to 1.5mm. A microwave of 2.45GHz was irradiated into the quartz glass tube reactor from the rectangular cavity resonator with 4 mm diameter tungsten electrode and the plasma was generated at its tip. The microwave was adjusted in appropriate power to maintain a certain substrate temperature. Diamond films were evaluated by Raman spectroscopy, Scanning Electron Microscope (SEM) and Laser Microscope (LM). As a result, the best orientation for epitaxial growth was found to be (100) which have film growth gradually and smooth surface. Whereas (111) face has polycrystalline film with irregularity growth and rough surface. The remaining H and C after CO synthesis satisfying H/C>20 is necessary to synthesized diamond using IL-MPCVD. The deposition rate was about 32 μm/h when both single crystal and polycrystalline diamond film were synthesized.

Effect of Interplay Between Isotropic Gases on Microstructural Evolution of Single Crystal Diamond

Homo‐epitaxial (100) single crystal diamond films of different isotopic (13C) compositions were synthesized by micro‐wave plasma chemical vapor deposition. An increase in 13C concentration (0 to 99%) demonstrated clear developments in microstructures. These are related to changes in: (i) morphology, (ii) residual strain and dislocations and (iii) mesoscopic defects. (i) was mainly through increased presence of steps/ledges and corresponding increase in surface roughness. This was accompanied by significantly higher residual strain and presence/energy of dislocations. 13C concentration also determined mesoscopic defects: presence of non‐(100) orientations, nature of grain boundaries and micro‐segregations of 13C and/or CH.A link has been established between various reproducible, experimental observations through stipulated increase in interfacial energy and stresses present at grain boundaries.

Slow Electron–Phonon Cooling in Superconducting Diamond Films

We have measured the electron–phonon energy-relaxation time, ${\boldsymbol{\tau }_{{{\rm eph}}}}$ , in superconducting boron-doped diamond films grown on silicon substrate by chemical vapor deposition. The observed electron–phonon cooling times vary from 160 ns at 2.70 K to 410 ns at 1.8 K following a ${\boldsymbol{T}^{ - 2}}$ -dependence. The data are consistent with the values of ${\boldsymbol{\tau }_{{{\rm eph}}}}$ previously reported for single-crystal boron-doped diamond films epitaxially grown on diamond substrate. Such a noticeable slow electron–phonon relaxation in boron-doped diamond, in combination with a high normal-state resistivity, confirms a potential of superconducting diamond for ultrasensitive superconducting bolometers.

Investigations of the co-doping of boron and lithium into CVD diamond thin films

Lithium has been incorporated into heavily boron-doped single-crystal (SCD), microcrystalline (MCD) and nanocrystalline diamond (NCD) films at concentrations up to ~2×1020cm−3 using Li3N as a solid-state Li source for in-diffusion and diborane as the B source. The quality, morphology, electrical resistance and concentration of B and Li dopants present in a range of B+Li co-doped SCD, MCD and NCD films have been studied. Analysis of the SIMS depth profiles for Li enabled the diffusion constants, D, to be measured (in units of cm2s−1) as: 2.5×10−15, 1.3×10−14 and 7.0×10−14 for SCD, MCD and NCD, respectively, at 1100K. The value for D for SCD agrees closely with that in the literature, while the much larger values for the polycrystalline films provide direct evidence that Li can diffuse rapidly along or through diamond grain boundaries at elevated temperatures. If prolonged diffusion allows the Li to reach the Si substrate, the Si acts as a sink for Li absorbing large quantities and reducing its concentration in the diamond film.

<italic>V</italic>2O5MISFETs on H-Terminated Diamond

We report for the first time on the dc and RF performance of novel MISFETs fabricated on hydrogen-terminated (H-terminated) single crystal diamond film using vanadium pentoxide (V2O5) as insulating material. The active devices were characterized in terms of static $I$ – $V$ characteristics and static transconductance as well as of S-parameters for the calculation of the maximum cutoff frequency and the maximum oscillation frequency. Time stability of the drain current was evaluated overnight observing a maximum fluctuation of 7%. Investigations on temperature dependence of diamond-based MISFET were also performed up to 130 °C. The experimental results were compared with the better established diamond MESFET technology. Finally, the surface transfer doping of H-terminated diamond by very thin V2O5 insulator was also investigated in terms of conductivity, stability in air, and resistance to high temperatures.

N-type control of single-crystal diamond films by ultra-lightly phosphorus doping

A wide impurity doping range of p- and n-type diamond semiconductors will facilitate the development of various electronics. This study focused on producing n-type diamond with ultra-lightly impurity doping concentrations. N-type single-crystal diamond films were grown on (111)-oriented diamond substrates by phosphorus doping using the optimized doping conditions based on microwave plasma-enhanced chemical vapor deposition with a high magnetron output power of 3600 W. The surface morphology was investigated by an optical microscopy using the Nomarski prism and confocal laser microscopy, and the phosphorus concentration was estimated by a secondary ion mass spectrometry. The phosphorus concentration was reproducibly controlled to between 2 × 1015 and 3 × 1017 cm−3 using a standard mass flow controller, and the average incorporation efficiency was around 0.1%. The electrical properties of the films were characterized by the Hall effect measurements as a function of temperature over a wide range from 220 to 900 K. N-type conductivity with thermal activation from a phosphorus donor level at around 0.57 eV was clearly observed for all the phosphorus-doped diamond films. The electron mobility of the film with a phosphorus concentration of 2 × 1015 cm−3 was recorded at 1060 cm2/V s at 300 K and 1500 cm2/V s at 225 K.

Configuration of a single grown-in dislocation corresponding to one etch pit formed on the surface of CVD homoepitaxial diamond

We present a detailed crystalline structure around one etch pit formed on the as-grown surface of a (001)-oriented chemical vapor deposition (CVD) homoepitaxial single crystal diamond film investigated using cross-sectional transmission electron microscopy (TEM). One threading dislocation corresponding to one pit is found, and it is shown that this dislocation line continuously runs from the apex of the pit to the deeper region in the film toward the substrate. The observed threading dislocation directs parallel to the approximate [001] film-growth direction, but is not a perfect straight line and propagates in a zig-zag manner. The contrast analysis of the dislocation in TEM micrographs is performed under several major two-beam reflections. These results suggest that the dislocation is composed of short segments of undissociated perfect dislocations with Burgers vectors b=1/2[110], 1/2[011] and 1/2[101] lying on the {111} glide plane and, as a whole, travels approximately parallel to the [001] direction.

Development and high temperature testing by 14 MeV neutron irradiation of single crystal diamond detectors

In the present paper, the performances of single crystal diamond detectors “ad hoc” designed to operate at high temperature are reported. The detectors were realized using commercial CVD single crystal diamond films, 500 micron thick with metal contacts deposited by sputtering method on each side. The new detector layout is based upon mechanical contacts between the diamond film and the electric ground. The detector was first characterized by measuring the leakage current as function of temperature and applied biasing voltage (I-V characteristics). The results obtained using two different metal contacts, Pt and Ag respectively, while irradiated with 14 MeV neutrons at the Frascati neutron generator (FNG) are reported and compared. It is shown that diamond detectors with Ag metal contacts can be properly operated in spectrometric mode up to 240̂C with energy resolution (FWHM) of about 3.5%.

Reprint of "Palladium Ohmic contact on hydrogen-terminated single crystal diamond film"

Contact properties of Palladium (Pd) on the surface of hydrogen-terminated single crystal diamond were investigated with several treatment conditions. 150nm Pd pad was deposited on diamond surface by thermal evaporation technique, which shows good Ohmic properties with the specific contact resistivity (ρc) of 1.8×10−6Ωcm2 evaluated by Transmission Line Model. To identify the thermal stability, the sample was annealed in Ar ambient from 300 to 700°C for 3min at each temperature. As the temperature increased, ρc firstly decreased to 4.93×10−7Ωcm2 at 400°C and then increased. The barrier height was evaluated to be −0.15eV and −0.03eV for as-deposited and 700°C annealed sample by X-ray photoelectron spectroscopy analysis. Several surface treatments were also carried out to determine their effect on ρc, among which HNO3 vapor treated sample indicates a lower value of 5.32×10−6Ωcm2.

Application of femtosecond laser technique in single crystal diamond film separation

In this paper, we report on an attempt to separate single crystal (SC) diamond film from diamond substrate by femtosecond laser treatment and electrochemical etching techniques. Firstly, femtosecond laser was focused on about 20μm below the surface of diamond substrate to form a non-diamond layer. Secondly, a thick SC diamond film was grown on this substrate by microwave plasma chemical vapor deposition system. Finally, an electrochemical etching treatment was performed to separate the SC diamond film from its substrate. The results indicate that femtosecond laser technique has provided a potential way for the separation of grown diamond film from its substrate.

Palladium Ohmic contact on hydrogen-terminated single crystal diamond film

Contact properties of Palladium (Pd) on the surface of hydrogen-terminated single crystal diamond were investigated with several treatment conditions. 150nm Pd pad was deposited on diamond surface by thermal evaporation technique, which shows good Ohmic properties with the specific contact resistivity (ρc) of 1.8×10−6Ωcm2 evaluated by Transmission Line Model. To identify the thermal stability, the sample was annealed in Ar ambient from 300 to 700°C for 3min at each temperature. As the temperature increased, ρc firstly decreased to 4.93×10−7Ωcm2 at 400°C and then increased. The barrier height was evaluated to be −0.15eV and −0.03eV for as-deposited and 700°C annealed sample by X-ray photoelectron spectroscopy analysis. Several surface treatments were also carried out to determine their effect on ρc, among which HNO3 vapor treated sample indicates a lower value of 5.32×10−6Ωcm2.

Low resistivity p+ diamond (100) films fabricated by hot-filament chemical vapor deposition

By hot-filament (HF) chemical vapor deposition (CVD), heavily boron (B)-doped single-crystal diamond (100) films were fabricated and their structural and electrical properties were studied. We did not observe the soot formation, which is frequently observed and limits the performances in the case of microwave plasma (MWP) CVD. The B concentration was successfully controlled over the range from 1019 to 1021cm−3. Hillock-free films were obtained, whose mean surface roughness measured by atomic force microscopy (AFM) was less than 0.1nm. From the reciprocal space mapping (RSM) around 113 diamond reflection, it was revealed that the films possess the smaller lattice expansion than that expected from the Vegard's law. The room-temperature resistivity was decreased lower than 1mΩ·cm for B concentration ~1021cm−3. These results indicate that the HFCVD possesses large potential for fabricating the device-grade p+ diamond.

Three-dimensional kinetic Monte Carlo simulations of diamond chemical vapor deposition.

A three-dimensional kinetic Monte Carlo model has been developed to simulate the chemical vapor deposition of a diamond (100) surface under conditions used to grow single-crystal diamond (SCD), microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films. The model includes adsorption of CHx (x = 0, 3) species, insertion of CHy (y = 0-2) into surface dimer bonds, etching/desorption of both transient adsorbed species and lattice sidewalls, lattice incorporation, and surface migration but not defect formation or renucleation processes. A value of ∼200 kJ mol(-1) for the activation Gibbs energy, ΔG(‡) etch, for etching an adsorbed CHx species reproduces the experimental growth rate accurately. SCD and MCD growths are dominated by migration and step-edge growth, whereas in NCD and UNCD growths, migration is less and species nucleate where they land. Etching of species from the lattice sidewalls has been modelled as a function of geometry and the number of bonded neighbors of each species. Choice of appropriate parameters for the relative decrease in etch rate as a function of number of neighbors allows flat-bottomed etch pits and/or sharp-pointed etch pits to be simulated, which resemble those seen when etching diamond in H2 or O2 atmospheres. Simulation of surface defects using unetchable, immobile species reproduces other observed growth phenomena, such as needles and hillocks. The critical nucleus for new layer growth is 2 adjacent surface carbons, irrespective of the growth regime. We conclude that twinning and formation of multiple grains rather than pristine single-crystals may be a result of misoriented growth islands merging, with each island forming a grain, rather than renucleation caused by an adsorbing defect species.

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.

Gate-Source Distance Scaling Effects in H-Terminated Diamond MESFETs

In this paper, an analysis of gate–source and gate–drain scaling effects in MESFETs fabricated on hydrogen-terminated single-crystal diamond films is reported. The experimental results show that a decrease in gate–source spacing can improve the device performance by increasing the device output current density and its transconductance. On the contrary, the gate–drain distance produces less pronounced effects on device performance. Breakdown voltage, knee voltage, and threshold voltage variations due to changes in gate–source and drain–source distances have also been investigated. The obtained results can be used as a design guideline for the layout optimization of H-terminated diamond-based MESFETs.