Single Crystal Diamond Films Research Articles

Molecular Dynamics Calculations of CH3 Sticking Coefficient onto Diamond Surfaces

A molecular dynamics model is implemented in a way dedicated to simulate initial conditions close to microwave plasma deposition of thick single crystal diamond films. The sticking coefficient of CH3 radical is obtained for (111) and (100) surface at three gas and substrate temperatures: 1 120, 1 200, and 1 500 K. A low value of 5.10−4 is obtained, which is consistent with experimental findings claiming values less than 0.01 or equating to 8.10−3 at 1 120 K.

Improvement of dislocation density in thick CVD single crystal diamond films by coupling H2/O2 plasma etching and chemo‐mechanical or ICP treatment of HPHT substrates

H2/O2 plasma treatments offer advantages over other etching processes of diamond as a technique to prepare the substrate's surface prior to homoepitaxial CVD diamond growth particularly in the case of thick films. It allows removing surface defects induced by polishing, thus leading to an improved morphology and limiting the stress within the grown crystal. Nevertheless, this treatment induces surface roughness leading to dislocation formation when CVD growth is initiated. In this paper we combined H2/O2 plasma etching with smoother surface treatment such as RIE‐ICP etching or Chemo‐Mechanical Polishing and we showed a significant reduction in dislocation density of the thick CVD epitaxial layers.

Incorporation of lithium and nitrogen into CVD diamond thin films

Abstract High concentrations of lithium (~ 5 × 1019 cm− 3) and nitrogen (~ 3 × 1020 cm− 3) have been simultaneously incorporated into single-crystal and microcrystalline diamond films using Li3N and gaseous ammonia as the sources of Li and N, respectively. Using sequential deposition methods, well-defined localised layers of Li:N-doped diamond with a depth spread of less than ± 200 nm have been created within the diamond. The variation in Li:N content and amount of diffusion within the various types of diamond suggests a model whereby these atoms can migrate readily through the grain-boundary network, but do not migrate much within the grains themselves where the diffusion rate is much slower. However, the high electrical resistivity of the doped films, despite the high Li and N concentrations, suggests that much of the Li and N are trapped as electrically inactive species.

Effect of Nitrogen on the Growth of Boron Doped Single Crystal Diamond

Boron-doped single crystal diamond films were grown homoepitaxially on synthetic (100) Type Ib diamond substrates using microwave plasma assisted chemical vapor deposition. A modification in surface morphology of the film with increasing boron concentration in the plasma has been observed using atomic force microscopy. Use of nitrogen during boron doping has been found to improve the surface morphology and the growth rate of films but it lowers the electrical conductivity of the film. The Raman spectra indicated a zone center optical phonon mode along with a few additional bands at the lower wavenumber regions. The change in the peak profile of the zone center optical phonon mode and its downshift were observed with the increasing boron content in the film. However, sharpening and upshift of Raman line was observed in the film that was grown in presence of nitrogen along with diborane in process gas.

Tunable light emission from nitrogen-vacancy centers in single crystal diamond PIN diodes

Charge-states modulation of nitrogen-vacancy (NV) centers incorporated into single crystal diamond films attracts increasing attention for solid-state qubits applications. Here, we discuss the electro- and photoluminescence emission properties of NV centers incorporated by gas phase nitrogen delta-doping of the intrinsic diamond layer of a positive-intrinsic-negative (PIN) junction diode. The experiments show that the charge state of NV centers can be intentionally controlled by applying well-defined external bias voltages. It can be switched from the negatively charged state NV− to the neutral charged state NV0 when a strong forward bias potential is applied. This can be switched back by application of reverse potentials. These results will be discussed assuming basic electronic properties of diamond PIN diodes, including the variation of spectral properties as well as the dynamics of charge state transitions.

Integrated High-Quality Factor Optical Resonators in Diamond

The realization of an integrated diamond photonic platform, based on a thin single crystal diamond film on top of a silicon dioxide/silicon substrate, is reported. Using this approach, we demonstrate high-quality factor single crystal diamond race-track resonators, operating at near-infrared wavelengths (1550 nm). The devices are integrated with low-loss diamond waveguides terminated with polymer pads (spot size converters) to facilitate in- (out-) coupling of light from (to) an optical fiber. Optical characterization of these resonators reveal quality factors as high as ~250,000 and overall insertion losses as low as 1 dB/facet. Scattering induced mode splitting as well as signatures of nonlinear effects such as optical bistability are observed at an input pump power of ~100 mW in the waveguides.

Hall Effect Measurement System for Characterization of Doped Single Crystal Diamond

ABSTRACTA temperature dependent Hall Effect measurement system with software based data acquisition and control was built and tested. Transport measurements are shown for boron-doped single crystal diamond (SCD) films deposited in a microwave plasma-assisted chemical vapor deposition (MPCVD) reactor. The influence of Ohmic contacts and temperature control accuracy are studied. For a temperature range of 300K-700K IV curves, Hall mobilities and carrier concentrations are presented.

Synthesis and Characterization of Boron-Doped Single Crystal Diamond

ABSTRACTThe boron-doped single crystal diamond films were grown homoepitaxially on synthetic (100) oriented Type Ib diamond substrates using a Microwave Plasma Chemical Vapor Deposition (MPCVD) technique. Raman spectrum showed a few additional bands at the lower wavenumber regions along with the zone center optical phonon mode for diamond. The change in the peak profile of the zone center optical phonon mode and its downshift were observed with the increasing boron content in the film. A modification in surface morphology of the film with increasing boron content had been observed by atomic force microscopy. Four point probe electrical measurement indicated that different conduction mechanisms are operating in various temperature regions for these semiconducting films.

Study of Boron Based Superconductivity and Effect of High Temperature Cuprate Superconductors

This paper illustrates the main normal and Boron superconducting state temperature properties of magnesium diboride, a substance known since early 1950's, but lately graded to be superconductive at a remarkably high critical temperature Tc=40K a binary synthesis. What makes MgB2 so special? Its high Tc, simple crystal construction, large coherence lengths, high serious current densities and fields, lucidity of surface boundaries to current promises that MgB2 will be a good material both large scale applications and electronic devices. Throughout the last seven month, MgB2 has been fabricated in various shape, bulk, single crystals, thin films, ribbons and wires. The largest critical current densities >10MA/cm2 and critical fields 40T are achieved thin films. The anisotropy attribution inferred from upper critical field measurements is still to be resolved, a wide range of values being reported, γ = 1.2 ÷ 9. Also there is no consensus about the existence of a single anisotropic or double energy cavity. One central issue is whether or not MgB2 represents a new class of superconductors, being the tip of an iceberg that waits to be discovered. Until now MgB2 holds the record of the highest Tc among simple binary synthesis. However, the discovery of superconductivity in MgB2 revived the interest in non-oxides and initiated a search superconductivity in related materials, several synthesis being already announced to become superconductive: TaB2, BeB2.75, C-S composites, and the elemental B under pressure. I. INTRODUCTIN High-temperature superconductors (abbreviated high-Tc or HTS) are materials that behave as superconductors at unusually high temperatures. The highest -Tc superconductor was discovered in 1986 by IBM researchers Karl Muller and Johannes Bednorz, who were awarded the 1987 Nobel Prize in Physics for their important break-through in the discovery of superconductivity in ceramic materials. Until 2008, only certain compounds of copper and oxygen (so-called cuprates) were believed to have HTS properties, and the term high-temperature superconductor was used interchangeably with cuprate superconductor compounds such as bismuth strontium calcium copper oxide (BSCCO) and yttrium barium copper oxide (YBCO). However, several iron-based compounds (the iron pnictides) are now known to be superconducting at high temperatures. Some cuprates have an upper critical field of 100 tesla. However, cuprate materials are brittle ceramics which are expensive to manufacture and not easily turned into wires or other useful shapes. In 2004, bridging the gap unraveling the super hardness and the superconducting communities, Ekimov et al exposed the superconducting behaviour of a diamond sample resulting from annealing graphite with B4C at 2500-2800 K under 8-9 GPa 5s. These authors planned also a mechanism the transformation of graphite into diamond at high pressure and high temperature (HPHT), and made a careful characterization of the diamond polycrystal . Similar results be reported shortly after polycrystalline and (100)-oriented single crystaldiamond films full-fledged by microwave plasma-assisted chemical vapour deposition (MPCVD), showing that zero resistivity could be experiential up to the boiling temperature of helium (4.2 K), that doping-induced superconductivity appeared above about 6 1020 B/cm3 and that Tc amplified with the Boron concentration.

Resistant and sensitive single-crystal diamond dosimeters for ionizing radiation

Diamond dosimeters for intense ionizing radiation were assembled by developing Ohmic contacts on single-crystal high-purity diamond films. Leakage electrical resistivity of the order of 1014Ωcm was measured. Devices were tested with a low-intensity 17.48keV X-ray beam to probe their maximum sensitivity and the minimum detectable dose-rate. Diamond detectors provided a linearity coefficient to X-ray dose-rate of 1.023±0.07, whose dependence on operative bias voltage is here analyzed.

Very Fast and Primingless Single-Crystal-Diamond X-Ray Dosimeters

X-ray dosimeters were developed by tailoring novel injecting diamond-like-carbon/Pt/Au contacts on single-crystal high-purity diamond films. A dark resistivity of (5.6 ± 0.1) × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> Ω · cm and no appreciable presence of deep traps in the bandgap confirmed a very low defect density in the diamond films. The dosimeters resulted to be primingless (i.e., no need of preactivation) and characterized by high sensitivity [(58.20 ± 3.26) × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> C · Gy <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ] and linear response to X-ray dose rate, produced by a molybdenum target. Transient X-ray modulated analysis allowed the determination of fast-trap influence and the estimation of very fast response times (~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> s), at electric fields ≥ 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> V/cm.

Integrated Diamond Networks for Quantum Nanophotonics

We demonstrate an integrated nanophotonic network in diamond, consisting of a ring resonator coupled to an optical waveguide with grating in- and outcouplers. Using a nitrogen-vacancy color center embedded inside the ring resonator as a source of photons, single photon generation and routing at room temperature is observed. Furthermore, we observe a large overall photon extraction efficiency (10%) and high quality factors of ring resonators (3200 for waveguide-coupled system and 12,600 for a bare ring).

Dopant Uniformity and Concentration in Boron Doped Single Crystal Diamond Films

ABSTRACTHigh quality single crystal boron-doped diamond films are deposited in a microwave plasma-assisted CVD reactor with feedgas mixtures including hydrogen, methane, diborane, and carbon dioxide at reactor pressures of 160 Torr. The effect of diborane levels and other growth parameters on the incorporated boron levels are investigated, and the doping efficiency is calculated over a wide range of boron concentrations. The boron level is investigated using infrared absorption, and compared to SIMS measurements, and defects are shown to affect the doping uniformity.

Characterization of a sandwich-type large CVD single crystal diamond particle detector fabricated using a lift-off method

Crystallinity of a freestanding large (size: ~9×7mm) undoped single crystal (SC) diamond film grown by plasma chemical vapor deposition (CVD) and radiation response of a sandwich-type radiation detector made from this SC plate to α particles were investigated. The freestanding SC film was formed by elimination of a substrate using a so-called “lift-off method” after the growth of a thick-film on a pre-ion-implanted substrate. The formed SC plate has a high optical transparency, indicating no remarkable optical absorption seen in the wavelength from ultraviolet to near-infrared region. In the energy spectra of 5.486MeV α-particles, relatively sharp peaks were observed for both hole and electron transits. For the hole transit, the peak resolution of the pulse height distribution and charge collection efficiency (CCE) were ~0.7% and 98%, respectively. On the other hand, for the electron transit, the peak resolution and CCE obtained were ~4.4% and 89%, respectively. In the photoluminescence spectrum at room temperature, a strong sharp peak around 235nm corresponding to free exciton and a weak visible band mainly related to nitrogen-vacancy complex were observed. The spectral width of the (004) plane X-ray rocking curve was 16.5″. The micrograph taken using crossed-polarizers demonstrated that there are some white regions and four-petaled patterns, originating from internal strain and most likely threading dislocations, respectively.

Study of Microstructures in Single Crystalline Chemical Vapor Deposited Diamond Thin Films

Homo-epitaxial (100) single crystal diamond films of different isotopic (13C) composition were synthesized by micro-wave plasma chemical vapor deposition (MPCVD). Undoped 12C (100) films were also synthesized at different thicknesses. The growth surface of 13C doped showed a sequential morphological change from flat surface to stepped or ledge surface and coarsening of the steps/ledges with the increase of 13C-isotope concentration. As the growth proceeds via surface steps/ledges and coarsening of these steps/ledges, further increase in imperfection of the grown CVD single crystal diamonds observed with the development of non-(100) orientations. In case of undoped 12C samples, as the thickness increased the in-grain misorientation got reduced.

Conducting boron-doped single-crystal diamond films for high pressure research

Epitaxial boron-doped diamond films were grown by microwave plasma chemical vapor deposition for application as heating elements in high pressure diamond anvil cell devices. To a mixture of hydrogen, methane and oxygen, diborane concentrations of 240–1200 parts per million were added to prepare five diamond thin-film samples. Surface morphology has been observed to change depending on the amount of diborane added to the feed gas mixture. Single-crystal diamond film with a lowest room temperature resistivity of 18 mΩ cm was fabricated and temperature variation of resistivity was studied to a low temperature of 12 K. The observed minima in resistivity values with temperature for these samples have been attributed to a change in conduction mechanism from band conduction to hopping conduction. We also present a novel fabrication methodology for monocrystalline electrically conducting channels in diamond and present preliminary heating data with a boron-doped designer diamond anvil to 620 K at ambient pressure.

Effect of argon addition on the growth of thick single crystal diamond by high‐power plasma CVD

AbstractDiamond films were synthesized with up to 50% argon in the gas phase using high power plasma‐assisted chemical vapour deposition (PACVD). This resulted in a strong increase of the deposition rates. Polycrystalline diamond (PCD) films grown with Ar have shown a higher incorporation of sp2 phases but with no dramatic change in crystal morphologies. Thick single crystal diamond films did not show any obvious change in crystal quality though. By using optical emission spectroscopy (OES) and plasma simulation, it was found that the gas temperature is increased by the addition of argon by at least 500 K. This in turn promotes dissociation of H2 into H‐atom as would be obtained from an increase of the plasma power density. High‐power PACVD with argon addition is thus an efficient technique for the fast growth of thick single crystal films without the cost and additional problems related to an increase of the injected microwave power.

Synthetic diamond X-ray dosimeter for radiotherapy

Abstract The performance of a synthetic diamond X-ray detector during typical clinical beam characterisation procedures was compared to the performance of standard clinical detectors; this diamond detector used a single crystal diamond film synthesised using chemical vapour deposition as its sensitive element. Measurements were performed using 6 MV photons from a Varian 600C linear accelerator. The procedures measured the dose profile with depth along the central axis in a phantom (tissue maximum ratio) for a 10 × 10 cm 2 field, variation in dose at the isocentre with field size (output factor), and dose profile across and beyond the X-ray beam (off-axis ratio) for 10 × 10 cm 2 and 1 × 1 cm 2 fields. Tissue maximum ratio values were within 0.8% of the values from a standard ion chamber, over a depth range of 1–15 cm. Output factors were measured for field sizes from 0.6 × 0.6 cm 2 to 15 × 15 cm 2 and agreed well ( 2 . Off-axis measurements showed reduced penumbral width when the lateral size of the detector was reduced by holding the diamond detector in an edge-on orientation; values were comparable to those obtained using a diode detector. Overall, these results demonstrate the potential of synthetic diamond detectors for clinical beam characterisation, particularly for small beam sizes.

Clinical investigations of a CVD diamond detector for radiotherapy dosimetry

X-ray detectors based on single crystal diamond film made via chemical vapor deposition were investigated to evaluate their performance under clinically relevant conditions for radiotherapy dosimetry. Studies focused on repeatability, dose rate dependence, tissue phantom ratios, output factors and beam profiling. Repeatability experiments revealed a temporary loss in sensitivity due to charge detrapping effects following irradiation, which was modeled to make corrections that improved short-term precision. Dose rate dependence was observed (Fowler fitting parameter Δ = 0.96 ± 0.2) using dose rates up to ∼2 Gy min^−1. The detector statistically distinguished (n = 5, P < 0.05) between dose values separated by 7.7 × 10^−3 Gy (1 MU). Depth dose measurements from 1 to 15 cm and output factors using 3 × 3 to 10 × 10 cm^2 field sizes compared well with a Farmer ion chamber (<1.3% difference). Output factor measurements indicate encouraging results for fields sizes <4 × 4 cm^2. Off-axis measurements showed that perturbation of the beam could be reduced when the detector is used in the edge-on orientation due to its thin-film sandwich configuration and ∼200 nm thick Ag contacts. This relatively inexpensive detector has potential to be used for routine dosimetry using conventional radiotherapy instrumentation.

Simulations of chemical vapor deposition diamond film growth using a kinetic Monte Carlo model and two-dimensional models of microwave plasma and hot filament chemical vapor deposition reactors

A one-dimensional kinetic Monte Carlo (KMC) 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 considers adsorption, etching/desorption, lattice incorporation and surface migration but not defect formation or renucleation processes. Two methods have been devised for estimation of the gas phase concentrations of species at the growing diamond surface, and are used to determine adsorption rates for C1Hx hydrocarbons for the different conditions. The rate of migration of adsorbed carbon species is governed by the availability of neighboring radical sites, which, in turn, depend upon the rates of H abstraction and of surface-radical migration. The KMC model predicts growth rates and surface roughness for each of diamond types consistent with experiment. In the absence of defect formation and renucleation the average surface diffusion length, ℓ, is a key parameter controlling surface morphology. When ℓ&amp;lt;2, surface migration is limited by the lack of availability of surface radical sites, and the migrating surface species simply hop back and forth between two adjacent sites but do not travel far beyond their initial adsorption site. Thus, Eley–Rideal processes dominate the growth, leading to the rough surfaces seen in NCD and UNCD. The maximum or “intrinsic” surface roughness occurs for nominally zero-migration conditions (ℓ=0) with an rms value of approximately five carbon atoms. Conversely, when migration occurs over greater distances (ℓ&amp;gt;2), Langmuir–Hinshelwood processes dominate the growth producing the smoother surfaces of MCD and SCD. By extrapolation, we predict that atomically smooth surfaces over large areas should occur once migrating species can travel approximately five sites (ℓ∼5). β-scission processes are found to be unimportant for MCD and SCD growth conditions, but can remove up to 5% of the adsorbing carbon for NCD and UNCD growth. C1Hx insertion reactions also contribute &amp;lt;1% to the growth for nearly all conditions, while C2Hx (x&amp;lt;2) insertion reactions are negligible due their very low concentrations at the surface. Finally, the predictions for growth rate and morphology for UNCD deposition in a microwave system were found to be anomalous compared to those for all the other growth conditions, suggesting that carbonaceous particulates created in these plasmas may significantly affect the gas chemistry.