Alexandre Tallaire

High quality MPACVD diamond single crystal growth: high microwave power density regime

The growth of monocrystalline diamond films of electronic quality and large thickness (>few hundreds of microns) is an important issue in particular for high-power electronics. In this paper, we will describe the different key parameters necessary to reach this objective. First, we will examine the deposition process and establish that only microwave assisted diamond deposition plasma reactors can achieve the optimal growth conditions for the efficient generation of the precursor species to diamond growth. Next, we will consider the influence of the monocrystalline diamond substrate orientation and quality on the growth of the epitaxial layer, especially when the deposited material thickness exceeds 100 µm. The need to use a specific pre-treatment procedure of the substrate before the growth and its impact will also be discussed. Finally we will look at the growth conditions themselves and assess the influence of the process parameters, such as the substrate temperature, the methane concentration, the microwave power density and the eventual presence of nitrogen in the gas phase, on both the morphology and quality of the films on the one hand and the growth rate on the other hand. For this, we will introduce the concept of supersaturation and comment on its evolution as a function of the process parameters.

Perfect preferential orientation of nitrogen-vacancy defects in a synthetic diamond sample

We show that the orientation of nitrogen-vacancy (NV) defects in diamond can be efficiently controlled through chemical vapor deposition growth on a (111)-oriented diamond substrate. More precisely, we demonstrate that spontaneously generated NV defects are oriented with a ∼97% probability along the [111] axis, corresponding to the most appealing orientation among the four possible crystallographic axes. Such a nearly perfect preferential orientation is explained by analyzing the diamond growth mechanism on a (111)-oriented substrate and could be extended to other types of defects. This work is a significant step towards the design of optimized diamond samples for quantum information and sensing applications.

Surface transfer doping of diamond by MoO3 : a combined spectroscopic and Hall measurement study

Surface transfer doping of diamond has been demonstrated using MoO3 as a surface electron acceptor material. Synchrotron-based high resolution photoemission spectroscopy reveals that electrons are transferred from the diamond surface to MoO3, leading to the formation of a sub-surface quasi 2-dimensional hole gas within the diamond. Ex-situ electrical characterization demonstrated an increase in hole carrier concentration from 1.00 × 1013/cm2 for the air-exposed hydrogen-terminated diamond surface to 2.16 × 1013/cm2 following MoO3 deposition. This demonstrates the potential to improve the stability and performance of hydrogen-terminated diamond electronic devices through the incorporation of high electron affinity transition metal oxides.

Magnetic imaging with an ensemble of nitrogen-vacancy centers in diamond

The nitrogen-vacancy (NV) color center in diamond is an atom-like system in the solid-state which specific spin properties can be efficiently used as a sensitive magnetic sensor. An external magnetic field induces Zeeman shifts of the NV center levels which can be measured using optically detected magnetic resonance (ODMR). In this work, we quantitatively map the vectorial structure of the magnetic field produced by a sample close to the surface of a CVD diamond hosting a thin layer of NV centers. The magnetic field reconstruction is based on a maximum-likelihood technique which exploits the response of the four intrinsic orientations of the NV center inside the diamond lattice. The sensitivity associated to a 1 μm2 area of the doped layer, equivalent to a sensor consisting of approximately 104 NV centers, is of the order of 2 μT/√Hz. The spatial resolution of the imaging device is 480 nm, limited by the numerical aperture of the optical microscope which is used to collect the photoluminescence of the NV layer. The effectiveness of the method is illustrated by the accurate reconstruction of the magnetic field created by a DC current inside a copper wire deposited on the diamond sample.Graphical abstract

Photonic nano-structures on (111)-oriented diamond

We demonstrate the fabrication of single-crystalline diamond nanopillars on a (111)-oriented chemical vapor deposited diamond substrate. This crystal orientation offers optimal coupling of nitrogen-vacancy (NV) center emission to the nanopillar mode and is thus advantageous over previous approaches. We characterize single native NV centers in these nanopillars and find one of the highest reported saturated fluorescence count rates in single crystalline diamond in excess of 106 counts per second. We show that our nano-fabrication procedure conserves the preferential alignment as well as the spin coherence of the NVs in our structures. Our results will enable a new generation of highly sensitive probes for NV magnetometry and pave the way toward photonic crystals with optimal orientation of the NV centers emission dipole.

Electro-optical response of a single-crystal diamond ultraviolet photoconductor in transverse configuration

Diamond has been identified as a very promising material for X and ultraviolet sensing. In this Letter, a photoconductive device based on a freestanding homoepitaxial chemically vapor deposition (CVD) single-crystal diamond 500μm thick has been tested. Photoconductive measurements in coplanar and transverse configurations have been performed to characterize the device sensitivity in the 140–250 nm spectral range. Very high sensitivity values were achieved in both configurations. The sensitivity in the transverse configuration is at least 300 times higher than in the coplanar configuration.

Growth of thick heavily boron-doped diamond single crystals: Effect of microwave power density

The fabrication of diamond-based vertical power devices which are the most suited for high current applications requires the use of thick heavily boron-doped (B-doped) diamond single crystals. Although the growth of thin B-doped diamond films is well controlled over a large concentration range, little is known about the growth conditions leading to heavily doped thick single crystals. In this paper, it was found that the microwave power densities (MWPD) coupled to the plasma used to synthesize B-doped diamond by chemical vapor deposition is one of the key parameters allowing tuning doping efficiencies over two orders of magnitude. At high MWPD (above 100 W cm−3) the boron doping efficiency (DE) is extremely low while further increasing the boron concentration in the gas phase is no use as this leads to plasma instability. On the other hand, when low MWPD are used (<50 W cm−3), DE can be strongly increased but twinning and defects formation hampers the surface morphology. The use of intermediate MWPD densi...

Enhanced surface transfer doping of diamond by V2O5 with improved thermal stability

Surface transfer doping of hydrogen-terminated diamond has been achieved utilising V2O5 as a surface electron accepting material. Contact between the oxide and diamond surface promotes the transfer of electrons from the diamond into the V2O5 as revealed by the synchrotron-based high resolution photoemission spectroscopy. Electrical characterization by Hall measurement performed before and after V2O5 deposition shows an increase in hole carrier concentration in the diamond from 3.0 × 1012 to 1.8 × 1013 cm−2 at room temperature. High temperature Hall measurements performed up to 300 °C in atmosphere reveal greatly enhanced thermal stability of the hole channel produced using V2O5 in comparison with an air-induced surface conduction channel. Transfer doping of hydrogen-terminated diamond using high electron affinity oxides such as V2O5 is a promising approach for achieving thermally stable, high performance diamond based devices in comparison with air-induced surface transfer doping.

Maskless and targeted creation of arrays of colour centres in diamond using focused ion beam technology

The creation of nitrogen-vacancy (NV) centres in diamond is nowadays well controlled using nitrogen implantation and annealing. Although the high-resolution placement of NV centres has been demonstrated using either collimation through pierced tips of an atomic force microscope (AFM) or masks with apertures made by electron beam lithography, a targeted implantation into pre-defined structures in diamond may not be achieved using these techniques. We show that a beam of nitrogen ions can be focused to approximately 100 nm using focused ion beam (FIB) technology. The nitrogen ion beam is produced using an electron cyclotron resonance (ECR) plasma source. Combined with a scanning electron microscope, the nitrogen-FIB offers new possibilities for the targeted creation of single defects in diamond. This maskless technology is suitable for example for the creation of optical centres in the cavities of photonic crystals or in diamond tips for scanning magnetometry.

Evaluation of freestanding boron-doped diamond grown by chemical vapour deposition as substrates for vertical power electronic devices

In this study, 4 × 4 mm2 freestanding boron-doped diamond single crystals with thickness up to 260 μm have been fabricated by plasma assisted chemical vapour deposition. The boron concentrations measured by secondary ion mass spectroscopy were 1018 to 1020 cm−3 which is in a good agreement with the values calculated from Fourier transform infrared spectroscopy analysis, thus indicating that almost all incorporated boron is electrically active. The dependence of lattice parameters and crystal mosaicity on boron concentrations have also been extracted from high resolution x-ray diffraction experiments on (004) planes. The widths of x-ray rocking curves have globally shown the high quality of the material despite a substantial broadening of the peak, indicating a decrease of structural quality with increasing boron doping levels. Finally, the suitability of these crystals for the development of vertical power electronic devices has been confirmed by four-point probe measurements from which electrical resisti...