Boron In Diamond Research Articles

Evaluating diffusion barriers of defects in boron ion implanted diamond

The potential of diamond for electronic materials can be realized by creating well-controlled p- or n-type doping profiles. p-type doping is achieved by ion implantation of boron followed by high temperature annealing to relax the lattice, reduce the defects and create active dopant sites by allowing diffusion of defects in the diamond crystal. It has been found that even after this diffusion the percentage of active dopant sites after high temperature annealing are only a small fraction of the total doping. We perform first principles density functional theory calculations and estimate the migration barrier energy (MBE) for diffusion of carbon vacancies, hydrogen, boron and their complexes in diamond including the boron‑carbon vacancy complex which was recently observed and predicted as a color center for qubit realization. These defects are commonly found after ion implantation of boron in diamond. Here, we use nudged elastic band (NEB) technique to estimate the MBE for these defects and use it to predict the corresponding annealing temperature. Our calculations correctly predict the MBE for carbon vacancy as compared to the available references in literature and extend the calculation to other defects predicted in ion implanted diamond. Our objective of evaluating the MBE is to predict the diffusion processes occurring during post-implantation annealing of diamond.

Intracenter dipole transitions of a hydrogen-like boron acceptor in diamond: Oscillator strengths and line broadening

Substitutional boron in diamond acts as an acceptor center with the ionization energy of about 372 meV. Unlike its analogues in elemental semiconductors (silicon, germanium), boron bound states are poorly described by the electronic mass approximation due to the large ionization energy and the small spin-orbit splitting of the valence band in diamond. Thereby experimental investigations appear to be a main way of study of discrete electronic states of boron in diamond.In this paper, we report infrared (IR) absorption spectroscopy results obtained for HPHT-grown single crystal diamonds doped with natural boron (80% 11B – 20% 10B), and with isotopically enriched boron (99% 11B – 1% 10B). A moderate dopant concentration (1016–1017 cm−3), low concentration of lattice defects and vanishing thermal impact at cryogenic temperatures provided significantly reduced line broadening so that more than 60 boron transitions could be spectrally resolved. Mathematical approximation of the spectral lines revealed the main empiric features of zero-phonon dipole intracenter transitions: their energy, linewidth and integrated absorption. This allowed us to calculate oscillator strength of the boron acceptor transitions in diamond. The Lorentzian shape of the spectral lines indicates dominating uniform broadening of the transitions. Together with the relatively broad linewidths (0.1–0.5 meV) it reveals strong electron-phonon interaction in boron-doped diamond.

共焦点ラマン分光法を用いたc-BN含有単結晶ダイヤモンド粒子の結晶性分析とTEM-EELS分析によるヘテロ界面の検討

Several theories have been proposed to synthesize diamond particles from graphite using a metal solvent（also called a catalyst, flux or dissolver）under high-pressure and high-temperature（HPHT）conditions. Many researchers support the “dissolution-precipitation” theory, by which graphitic carbon dissolves in molten metal and subsequently precipitates in diamond form. An alternative is Hosomi's theory: solid state nucleation occurs to form diamond crystals. This study uses confocal Raman spectroscopy to examine the crystallinity of cubic boron nitride （c-BN）contained in a single-crystal diamond matrix synthesized using HPHT method according to Hosomi's theory. We also observed theheterointerface between c-BN and the diamond matrix using transmission electron microscopy to assess the type of bonding present. Constituent elements and the local chemical bonding state were examined using electron energy loss spectroscopy. Results demonstrated that the c-BN and diamond were not bonded directly, but revealed an approx. 5-nm-thick boron-based compound（or amorphous）layer at the interface. The respective concentrations of boron in diamond and carbon in c-BN were below the detection limits, indicating no effect on the crystallinity of either material under the HPHT conditions.

The Frenkel–Poole Effect in the Ionization of an Acceptor Impurity of Boron in Diamond in a Strong Electric Field

The conductivity of epitaxial diamond films lightly doped with boron has been studied at strong electric fields up to ~5 × 105 V/ cm. It is shown that field ionization of boron acceptors in diamond at room temperature, because of the low concentration of free holes and the high binding energy of boron, occurs due to the Frenkel–Poole effect.

Large substitutional impurity isotope shift in infrared spectra of boron-doped diamond

Isotopic enrichment offers cutting-edge properties of materials opening exciting research and development opportunities. In semiconductors, reached progress of ultimate control in growth and doping techniques follows nowadays the high level isotopic purification. This requires deep understanding of isotopic disorder effects and techniques of their effective determination. Isotopic content of both crystal lattice and impurity centers cause the effects, which can be examined by different optical techniques. While disorder in the host lattice can be straight forward evaluated by inelastic light scattering or by SIMS measurements, determination of isotopic contributions of many orders less presented impurities remains challenging and usually observed in high-resolution photoluminescence or optical absorption spectra. Boron-doped diamonds exhibit complex infrared absorption spectra while boron-related luminescence remains unobserved. Boron, as a most light element acting as a hydrogen-like dopant in elemental semiconductors, has a largest relative difference in its isotope masses, and by this, cause the largest isotopic disorder in semiconductors, including diamond, an elemental semiconductor with the lightest atomic mass of a host lattice. This enables an access to the isotopic constitution of boron in diamond by infrared absorption spectroscopy. By comparison of low-temperature absorption spectra of a natural (20% of 10B and 80% of 11B isotopes) and 11B enriched (up to 99%) doped diamonds we differentiate the intracenter transitions related to 10B and to 11B isotopes. We have found that the isotopic spectral lines of the same boron intracenter transition are separated with the energy of about 0.7 meV. This is the largest impurity isotopic shift ever observed in semiconductors doped by hydrogen-like impurity centers.

Synthetic boron-doped carbonado, a new electrode material: synthesis in C–metal–B growth systems aimed at the lowering of the synthesis temperature without loss of electrochemical activity

New electrode material—boron-doped synthetic carbonado (bulk polycrystalline diamond)—was synthesized at high pressures and high temperatures in the C–metal (Co, Ni, or Fe) –B growth systems. The metal borides were used as the growth medium-forming substances for graphite-to-diamond transformation at a temperature of ~ 1300 °C and pressure of 8 GPa. For comparison, etalon carbonado-type electrode with nearly limiting concentration of boron in diamond was synthesized by subjecting the mixture of amorphous boron with graphite to much higher temperatures (2200–2500 °C) under the same pressure. Despite the lower content of boron in diamond synthesized in the presence of metal borides, these new boron-doped carbonado electrodes are not inferior to the etalon compact in their electrochemical activity, as judging by the onset potential of anodic chlorine evolution from KCl solution. The presence of metal-containing structural defects in boron-doped diamond matrix is supposed to be responsible for the somewhat enhanced catalytic activity of the electrodes. High-pressure synthesis of bulk metal-modified boron-doped diamond opens a new avenue in the development of superior functional electrode materials.

Characterization of electronic properties of natural type IIb diamonds

Precision admittance spectroscopy measurements were carried out over wide temperature and frequency ranges for a set of natural single crystal type IIb diamond samples. Peaks of conductance spectra vs. temperature and frequency were used to compute the Arrhenius plots, and activation energies were derived from these plots. The capacitance-voltage profiling was used to estimate the majority charge carrier concentration and its distribution into depth of the samples. Apparent activation energies between 315 and 325meV and the capture cross section of about 10−13cm2 were found for samples with uncompensated boron concentrations in the range of 1 to 5×1016cm−3 (0.06–0.3ppm). The obtained boron concentrations are in good coincidence with FTIR results for the samples. Also, a reason for the difference between the observed admittance activation energy and the previously reported ionization energy for the acceptor boron in diamond (0.37eV) is proposed.

Analysis of boron in diamond with UV photoluminescence

Photoluminescence (PL) spectra of boron-doped diamonds at temperature 298 K were recorded with excitation in wavelength range 110–300 nm from a synchrotron source. A prominent emission feature was measured at 480.0 nm, corresponding to energy 2.535 eV; we detected also a distinct photoluminescence excitation (PLE) band at 220.5 nm, 5.623 eV, for the first time. For sensitive analysis, the UV-PL technique provides a non-destructive method; we therefore recommend the use of UV-PL spectra excited in the region 200–230 nm to analyze boron dopant in diamonds. The least detectable concentration of the boron dopant is about 1 × 1016 atoms cm−3.

β-NMR study of boron in diamond

A β-NMR study of 12B implanted in diamond was performed in order to investigate the implantation sites and the defects. The maintained polarization of 12B was measured by use of widely modulated rf around the Larmor frequency (ν = νL ± 200 kHz) as a function of temperature from 160 K to 320 K. The observed polarization was found to be almost constant at about 0.9 % in this temperature range. The initial polarization for this system was obtained as about 8.1 %. Therefore about 10 % of the implanted 12B maintained its polarization in this frequency range. Conversely, about 90 % of the implanted 12B was undetected in the present experiment.

Highly-focused boron implantation in diamond and imaging using the nuclear reaction 11B(p, α)8Be

Diamond is an especially attractive material because of its gemological value as well as its unique mechanical, chemical and physical properties. One of these properties is that boron-doped diamond is an electrically p-type semiconducting material at practically any boron concentration. This property makes it possible to use diamonds for multiple industrial and technological applications. Boron can be incorporated into pure diamond by different techniques including ion implantation. Although typical energies used to dope diamond by ion implantation are about 100keV, implantations have also been performed with energies above MeV. In this work CMAM microbeam setup has been used to demonstrate capability to implant boron with high energies. An 8MeV boron beam with a size of about 5×3μm2 and a beam current higher than 500pA has been employed while controlling the beam position and fluence at all irradiated areas. The subsequent mapping of the implanted boron in diamond has been obtained using the strong and broad nuclear reaction 11B(p, α)8Be at Ep=660keV. This reaction has a high Q-value (8.59MeV for α0 and 5.68MeV for α1) and thus is almost interference-free. The sensitivity of the technique is studied in this work.

Growth and electrical characterisation of δ-doped boron layers on (111) diamond surfaces

A plasma enhanced chemical vapor deposition protocol for the growth of δ-doping of boron in diamond is presented, using the (111) diamond plane as a substrate for diamond growth. AC Hall effect measurements have been performed on oxygen terminated δ-layers and desirable sheet carrier densities (∼1013 cm−2) for field-effect transistor application are reported with mobilities in excess of what would expected for equivalent but thicker heavily boron-doped diamond films. Temperature-dependent impedance spectroscopy and secondary ion mass spectroscopy measurements show that the grown layers have metallic-like electrical properties with high cut-off frequencies and low thermal impedance activation energies with estimated boron concentrations of approximately 1020 cm−3.

Dissolution of boron in diamond under high pressures: experimental evidences

Dissolution of boron in diamond under high pressures: experimental evidences

Erratum: Ultimate Metastable Solubility of Boron in Diamond: Synthesis of Superhard DiamondlikeBC5[Phys. Rev. Lett.102, 015506 (2009)

Erratum: Ultimate Metastable Solubility of Boron in Diamond: Synthesis of Superhard Diamondlike<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>BC</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:math>[Phys. Rev. Lett.<b>102</b>, 015506 (2009)

Numerical Parameterization of Chemical-Vapor-Deposited (CVD) Single-Crystal Diamond for Device Simulation and Analysis

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> High-quality electronic-grade intrinsic chemical-vapor-deposited (CVD) single-crystal diamond layers having exceptionally high carrier mobilities have been reported by Isberg <etal/> This makes the realization of novel electronic devices in diamond, particularly for high-voltage and high-temperature applications, a viable proposition. As such, material models which can capture the particular features of diamond as a semiconductor are required to analyze, optimize, and quantitatively design new devices. For example, the incomplete ionization of boron in diamond and the transition to metallic conduction in heavily boron-doped layers require accurate carrier freeze-out models to be included in the simulation of diamond devices. Models describing these phenomena are proposed in this paper and include numerical approximation of intrinsic diamond which is necessary to formulate doping- and temperature-dependent mobility models. They enable a concise numerical description of single-crystal diamond which agrees with data obtained from material characterization. The models are verified by application to new Schottky <formula formulatype="inline"><tex Notation="TeX">$\hbox{m-i-p}^{+}$</tex></formula> diode structures in diamond. Simulated forward characteristics show excellent correlation with experimental measurements. In spite of the lack of impact ionization data for single-crystal diamond, approximation of avalanche coefficient parameters from other wide-bandgap semiconductors has also enabled the reverse blocking characteristics of diamond diodes to be simulated. Acceptable agreement with breakdown voltage from experimental devices made with presently available single-crystal CVD diamond is obtained. </para>

Highly and heavily boron doped diamond films

From the high ionization energy E i = 0.368 eV and high solid solubility ≥ 1.4 × 10 22 cm − 3 of boron in diamond, metallic conductivity is expected on the boron impurity band within the band gap (Mott model). On the contrary, the numerical models used to describe the superconductivity of metallic diamond mainly use the Bardeen model with a Fermi level within the valence band. Taking into account the decrease to zero of E i through the high [B] range and the band gap narrowing through the high and heavy [B] ranges, both specific of the Bardeen model, we discuss the validity of the Mott and Bardeen models from the literature and cathodoluminescence and Raman experiments. They agree with the Mott rather than the Bardeen model. Several experiments independently show the coupling of boron related levels with the zone centre optical phonons which soften for heavy [B]. The Mott model might explain the similar range of the superconductivity temperature of homoepitaxial and polycrystalline films from the similarity of their boron impurity band.

Boron spectral density and disorder broadening in B-doped diamond

Comparison of periodic B dopants with a random alloy of substitional boron in diamond is carried out using several supercells and the coherent potential approximation (CPA) for the random alloy case. The main peak in the B local density of states is shifted to lower binding energy compared to the corresponding C peak in intrinsic diamond. In supercells, this shows up as strongly B-character bands split from bulk C bands away from the zone center, in an energy region around $\ensuremath{-}1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Even for a $4\ifmmode\times\else\texttimes\fi{}4\ifmmode\times\else\texttimes\fi{}4$ supercell $({\mathrm{BC}}_{127})$, effects of the dopant order are evident in the form of primarily B-character bands just below the Fermi level at the supercell zone boundary. The bands resulting from the CPA are of continuous mixed C-B character. They resemble virtual crystal bands, but broadened somewhat reflecting the disorder-induced lifetime, and are consistent with angle-resolved photoemission band maps. The B character is 1.7 times larger than for C (per atom) near the top of the valence bands for CPA, and roughly the same for supercells. CPA results are particularly useful since they characterize the wave vector and energy dependence of disorder broadening.

Molecular dynamics simulation on boron diffusion in diamond

The atomic-scale diffusion mechanism of boron in diamond is investigated by molecular dynamics simulation. A substitutional boron atom diffuses to the self-interstitial site when there exists a self-interstitial carbon atom in its nearest tetrahedral center and the system temperature is high. More important, the bond between boron and the self-interstitial carbon atom is never broken during the diffusion process, indicating that B s–C i pairs diffuse in the lattice by the interstitial mechanism. The results suggest that boron diffusion is mediated by carbon self-interstitial and not by the vacancy mechanism. In addition, the estimated activation energy and the diffusion exponential prefactor of boron diffusion in diamond are found to be 0.23 eV and 1.123×10 −6cm 2/s, respectively.

High-performance diamond/amorphous silicon p-n+ heterojunctions

We have fabricated high-performance p–n+ heterojunctions of homoepitaxial diamond (B-doped film: p type) and hydrogenated amorphous silicon (P-doped a-Si:H film: n type). Current–voltage (I–V) characteristics of the p–n+ heterojunctions at room temperature show excellent rectification properties with an ideality factor n of 1.23 and undetectable leakage current at reverse bias condition. Capacitance–voltage (C–V) characteristics show a large difference of space-charge densities (net acceptor densities) in the bulk and near-surface (interface) regions of the diamond films and a strong frequency dependence in the forward-bias region. The former result indicates that the hydrogen passivation of boron in diamond during the a-Si:H deposition occurs in the near-surface region which gives rise to a reduction of the acceptor density in the depletion region. The latter result indicates an increment of hydrogen-related defect states in the near-surface region of the diamond film. An idealized energy-band diagram for the p–n+ heterojunctions has been constructed on the basis of the negative-electron-affinity model.

Boron-hydrogen complexes in diamond

Boron in diamond traps hydrogen forming passive ${\mathrm{B}}_{s}$-H pairs. Boron trapping two deuterium atoms has been speculated as forming a shallow donor (0.23--0.34 eV below the conduction band). We present the results of first-principles calculations of boron complexes with 2--4 hydrogen atoms. The binding energy of the second and subsequent H atoms is small and none of the structures found are shallow donors. We also present the structure of interstitial boron, the boron-vacancy complex, and their interaction with hydrogen.

A molecular dynamics study of interstitial boron in diamond

The stable configuration of an interstitial boron atom in diamond has been investigated by molecular dynamics simulation. The Tersoff potential is used to model the boron-carbon binary system. The results show that the interstitial boron, with its initial location at the tetrahedral or hexagonal center, intends to substitute for the carbon atom in the lattice, and it preferably forms a 〈0 0 1〉 split interstitial configuration. The total energy of the system with a stable substitutional-B-self-interstitial (B s–C i) complex is 0.14 eV higher than that of the system with the boron 〈0 0 1〉 split interstitial. It is concluded that the stable structure for an interstitial boron atom in diamond is the 〈0 0 1〉 split interstitial configuration, while neither the tetrahedral nor the hexagonal interstitial structure is stable.