High-pressure High-temperature Diamond Research Articles

CVD diamond optics for ultraviolet

The optical properties of CVD polycrystalline diamond have been studied in order to evaluate the feasibility of diamond mirrors operating in the UV spectral region. Diamond is a very attractive material for space application, since it offers a unique combination of high UV reflectivity, low reflectivity and high transmittance in the visible, mechanical hardness and chemical inertness. In addition, diamond has a high thermal conductivity, which should stabilize the refractive index. The UV reflectance at normal incidence and at 45°, the polarization degree and the transmittance in the visible of some CVD diamond samples have been measured. Opaque and transparent highly polished diamonds have been tested in order to evaluate the contribution of non-diamond carbon to the reflectance. The results have also been compared to the reflectance curves obtained using a high-pressure high-temperature (HPHT) single-crystal diamond to evaluate the influence of scattering from the polished surface of the CVD diamond layers.

Photoluminescence excitation study of cobalt-related optical centers in high-pressure high-temperature diamond

Abstract The results of a photoluminescence excitation (PLE) study of cobalt–nitrogen optical centers in high-pressure high-temperature (HPHT) treated synthetic diamonds are presented. A single vibronic band with zero-phonon line (ZPL) at 3.085 eV was found in the PLE for the 2.367 eV system and two bands with ZPLs at 3.004 and 3.673 eV for the 2.277 eV system. From the continuum excitation threshold the ground state was tentatively located at 4.3 and 4.45 eV below the conduction band for the 2.277 and 2.367 eV systems, respectively. For the minor photoluminescence bands with ZPLs at 2.207 and 2.135 eV general features of the PLE spectra were established.

Structural and Functional Characterization of HPHT Diamond Crystals Used in Photoconductive Devices

Diamond films are extensively studied for applications as functional material for UV photoconductors. CVD-grown polycrystalline diamond films show very interesting performances, but their complete exploitation is actually limited by a slow time response if compared to other materials, by a relatively high concentration of structural defects, impurities and grain boundaries, which may affect the collection length of photogenerated charges. High-quality single crystal diamonds could solve some of these problems. The absence of grain boundaries can produce longer collection lengths. The nitrogen and impurity contents can be reduced and then large type-IIa diamond single-crystals can be obtained. In this work, a detailed structural and functional characterization of type Ib HPHT diamond crystals has been carried out and the results have been compared to similar characterizations of CVD films to evaluate the different behavior, taking also into account that these high pressure high temperature (HPHT) diamond crystals contain several tens ppm of nitrogen.

Atom-by-atom analysis of diamond, graphite, and vitreous carbon by the scanning atom probe

Various artificial diamonds, graphite and vitreous carbon were atom-by-atom mass analyzed by a scanning atom probe (SCAP). Carbon clusters were detected in all specimens and the abundance of the clusters was found to be high for graphite and vitreous carbon. Nearly 90% of the carbon atoms field evaporated from 99.99% pure graphite were detected as clusters up to C11. After soaking in acid (H2SO4:HNO3:H2O=1:1:1) for 15 min no clusters were detected in the high-pressure high-temperature (HPHT) diamond which exhibited mass peaks of the clusters up to C6. The number of clusters formed by odd numbers of carbon atoms was larger than that formed by even numbers. The hydrogen concentration in chemically vapor deposited diamonds appeared to be related to the percentage of hydrogen in the mixed reaction gas while growing the diamonds. Few hydrogen ions were detected in the HPHT diamond and vitreous carbon. The hydrogen and oxygen distributions in the 99.8% graphite were rather uniform while those in the 99.99% graphite were localized. The present results suggest that the mass analysis by the SCAP may shed light on even the binding state of the analyzed materials.

Things we still don’t know about optical centres in diamond

Abstract In this article the optical spectra associated with some of the major defects in diamond are considered. In particular, we deal with isolated substitutional boron, isolated substitutional nitrogen and the nitrogen aggregates, the self-interstitial and defect complexes involving the self-interstitial with nitrogen or boron. Although some aspects of the spectra are understood, many puzzles and inconsistencies remain. The absorption bands responsible for the colours of natural pink and amber diamonds are discussed and studies of transition metal complexes in high-pressure high-temperature synthetic diamond are briefly mentioned.

CV and DLTS Experiments in Boron-Doped Diamond

Capacitance–voltage (CV) and deep level transient spectroscopy (DLTS) experiments are applied to explore various properties of boron-doped type IIb high-pressure high-temperature diamond and of homoepitaxially grown boron-doped CVD diamond: contact properties of Al contacts, acceptor density determination, energy distributions and densities of compensating defects and the interaction of boron acceptors with atomic hydrogen (deuterium). Two distinct excitation energies at 0.9 and 1.25 eV are detected by DLTS and optically excited DLTS. We propose a defect/acceptor model where holes are optically excited from defects 1.25 eV above the valence band edge either into ionized boron acceptors at 0.36 eV above EV (optical excitation ≈︂0.9 eV) or directly into the valence band (photon energy ≥1.25 eV). We also discuss the decrease of the capacitance after deuteration as detected by CV measurements based on deuterium–boron complex formation.

CV and DLTS Experiments in Boron-Doped Diamond

Capacitance–voltage (CV) and deep level transient spectroscopy (DLTS) experiments are applied to explore various properties of boron-doped type IIb high-pressure high-temperature diamond and of homoepitaxially grown boron-doped CVD diamond: contact properties of Al contacts, acceptor density determination, energy distributions and densities of compensating defects and the interaction of boron acceptors with atomic hydrogen (deuterium). Two distinct excitation energies at 0.9 and 1.25 eV are detected by DLTS and optically excited DLTS. We propose a defect/acceptor model where holes are optically excited from defects 1.25 eV above the valence band edge either into ionized boron acceptors at 0.36 eV above EV (optical excitation ≈0.9 eV) or directly into the valence band (photon energy ≥1.25 eV). We also discuss the decrease of the capacitance after deuteration as detected by CV measurements based on deuterium–boron complex formation.

Point Defects in Natural and Synthetic Diamond: What They Can Tell Us about CVD Diamond

More than 30 years of research on point defects in natural and high pressure, high temperature (HPHT) synthetic diamond helps us to characterise diamond produced by chemical vapour deposition (CVD). Nitrogen is the most common impurity in natural diamond, but hydrogen and boron are also detected. In HPHT diamond, nickel or cobalt complexes are seen as well. Irradiation produced interstitials and vacancies, which can help to identify some native defects. CVD diamond also may contain nitrogen and boron. A prominent defect, not normally seen in natural diamonds, is due to a silicon-vacancy complex. There are some hydrogen-related lines in the EPR spectra, which are peculiar to polycrystalline diamond and appear to arise near grain boundaries. Vacancies are seen close to the growth surfaces of particularly good quality CVD diamonds, although they are not present in the bulk of the diamond. Experience of vacancy migration in natural diamond allows us to explain this phenomenon.

The irradiation and annealing of Si-doped diamond single crystals

Abstract An isochronal annealing study was carried out on electron-irradiated Si-doped high-pressure high-temperature diamonds, measuring PL spectra and the absorption spectra.

Cathodoluminescence from high-pressure synthetic and chemical-vapor-deposited diamond

The nature of an UV cathodoluminescence band, which can appear in both boron-doped high-pressure high-temperature (HPHT) synthetic diamond and boron-doped diamond grown by chemical-vapor-deposition (CVD) techniques, is investigated. The band has a peak energy at 4.6 eV (270 nm), a full width at half-maximum of ∼0.4 eV and at low temperatures (∼130 K) can represent the overwhelmingly dominant cathodoluminescence (CL) from selected regions of a given sample. The band has been examined from boron-doped HPHT diamond grown from different solvent catalysts and from boron-doped CVD diamond grown under a variety of deposition conditions. Low-temperature spatially resolved CL imaging, using a scanning electron microscope with CL attachment, has revealed a clear growth-sector dependence of the 4.6 eV band in HPHT diamond. Using this technique an investigation of the relationship between this band and other commonly observed CL bands has been carried out. The band has an interesting temperature dependence which is investigated over the temperature range 77–300 K and explained in terms of competition between exciton capture and exciton release at some unidentified trapping center.