Franck Omnès

Direct observation of the core structures of threading dislocations in GaN

Here we present the first direct observation of the atomic structure of threading dislocation cores in hexagonal GaN. Using atomic-resolution Z-contrast imaging, dislocations with edge character are found to exhibit an eight-fold ring core. The central column in the core of a pure edge dislocation has the same configuration as one row of dimers on the {10-10} surface. Following recent theoretical work, it is proposed that edge dislocations do not have deep defect states in the band gap, and do not contribute to cathodoluminescence dislocation contrast. On the other hand, both mixed and pure screw dislocations are found to have a full core, and full screw dislocation cores were calculated to have states in the gap.

Extreme dielectric strength in boron doped homoepitaxial diamond

The fabrication of Schottky diodes withstanding breakdown voltages up to 10 kV is demonstrated. A corresponding electric field of 7.7 MV/cm at the center of the diode is evaluated with the help of a two-dimensional finite elements software. These properties result from a net shallow acceptor concentration below 10(16) cm(-3) in the first micrometers of an epitaxial film with optimized crystalline quality and a special oxidizing treatment of its surface, allowing the true dielectric strength of bulk diamond to be revealed.

High hole mobility in boron doped diamond for power device applications

Low boron doped homoepitaxial diamond layers were grown on Ib (100) diamond substrates with oxygen added to the gas mixture. The acceptor density of the samples has been estimated by C(V) and Hall effect to lie close to 1016 cm−3 with a maximum low field Hall mobility value of 1870 cm2/V s at 292 K. The presence of oxygen in the gas phase is shown to be a key parameter to obtain such characteristics. The mobility parameters required to simulate the electrical behavior of devices between 300 K and 500 K are then determined for a wide doping range.

Wide bandgap UV photodetectors: a short review of devices and applications

Ultraviolet detectors are of a great interest to a wide range of industrial, military, environmental and even biological applications. This paper intends first to review some of the most relevant recent developments in the field of wide bandgap semiconductor UV detectors, and to give an overview of their applications. A special focus is given on III-nitride based devices, which more and more clearly represent to date one of the most promising and flexible technical solutions for UV detection.

The Diamond Superconducting Quantum Interference Device

Diamond is an electrical insulator in its natural form. However, when doped with boron above a critical level (∼0.25 atom %) it can be rendered superconducting at low temperatures with high critical fields. Here we present the realization of a micrometer-scale superconducting quantum interference device (μ-SQUID) made from nanocrystalline boron-doped diamond (BDD) films. Our results demonstrate that μ-SQUIDs made from superconducting diamond can be operated in magnetic fields as large as 4 T independent of the field direction. This is a decisive step toward the detection of quantum motion in a diamond-based nanomechanical oscillator.Soumen Mandal ∗ , Tobias Bautze, Oliver A. Williams, Cécile Naud, Étienne Bustarret, Franck Omnès, Pierre Rodière, Tristan Meunier, Christopher Bäuerle ∗ , and Laurent Saminadayar Institut Néel, CNRS et Université Joseph Fourier, F-38042 Grenoble, France Fraunhofer-Institut für Angewandte Festkörperphysik, Tullastraße 72, 79108 Freiburg, Germany and Institut Universitaire de France, 103 boulevard Saint-Michel, 75005 Paris, France

Formation of oriented nanostructures in diamond using metallic nanoparticles

A simple, fast and cost-effective etching technique to create oriented nanostructures such as pyramidal and cylindrical shaped nanopores in diamond membranes by self-assembled metallic nanoparticles is proposed. In this process, a diamond film is annealed with thin metallic layers in a hydrogen atmosphere. Carbon from the diamond surface is dissolved into nanoparticles generated from the metal film, then evacuated in the form of hydrocarbons and, consequently, the nanoparticles enter the crystal volume. In order to understand and optimize the etching process, the role of different parameters such as type of catalyst (Ni, Co, Pt, and Au), hydrogen gas, temperature and time of annealing, and microstructure of diamond (polycrystalline and nanocrystalline) were investigated. With this technique, nanopores with lateral sizes in the range of 10-100 nm, and as deep as about 600 nm, in diamond membranes were produced without any need for a lithography process, which opens the opportunities for fabricating porous diamond membranes for chemical sensing applications.

Nanostructures made from superconducting boron-doped diamond

We report on the transport properties of nanostructures made from boron-doped superconducting diamond. Starting from nanocrystalline superconducting boron-doped diamond thin films, grown by chemical vapour deposition, we pattern by electron-beam lithography devices with dimensions in the nanometer range. We show that even for such small devices, the superconducting properties of the material are well preserved: for wires of width less than 100 nm, we measure critical temperatures in the kelvin range and critical fields in the tesla range.

Effects of the buffer layers on the performance of (Al,Ga)N ultraviolet photodetectors

The fabrication of (Al,Ga)N-based metal–semiconductor–metal (MSM) photovoltaic detectors requires the growth of high-quality (Al,Ga)N films. Inserting a low-temperature deposited buffer layer enables the growth of an epitaxial layer with a reduced density of defects. Two structures using GaN and AlN buffer layers have been deposited by low-pressure metalorganic chemical vapor deposition and used to fabricate MSM interdigitated detectors. The devices have been characterized to investigate the effects of the buffer layers on the detector performances.

New one step functionalization of polycrystalline diamond films using amine derivatives

Diamond received tremendous interest for analytical sciences due to its intrinsic properties. However, the analytical perception of chemical environment requires surface functionalization that brings selectivity to the detection event. Thereby, many works focused on diamond modification using chemical or biochemical entities. We proposed here, a new and straightforward methodology for diamond (bio)functionalization. This method involves the chemical reaction between (bio)chemical entities presenting a primary amine moiety, used as grafting site, and hydrogenated diamond surface. This reaction allows in one step to modify diamond surface whatever its doping level and its crystalline quality. The effectiveness of this new method is exposed here through the grafting of one redox species, ferrocene, and of one biochemical, biotin. The impacts of both functionalization duration and pH are investigated and the robustness of the formed bond is demonstrated owing to biotin-avidin coupling.

In situ characterization by reflectance difference spectroscopy of III–V materials and heterojunctions grown by low pressure metal organic chemical vapour deposition

Abstract The reflectance difference spectroscopy (RDS) technique has recently been used successfully to study the molecular beam epitaxial growth of GaAs and AlAs. An extension of such in situ characterization to the metal organic chemical vapour deposition (MOCVD) growth of III–V compounds would be very helpful, because electronic measurements such as reflection high energy electron diffraction are not possible in the MOCVD growth environment. In this paper preliminary results are reported of RDS studies performed in a low pressure MOCVD reactor under optimal growth conditions. The RDS signatures of GaInAsInP and GaAsGaInP heterojunctions and superlattices are presented for the first time. It is possible using the RDS technique to determine in situ the ⪡011⪢ and ⪡01 1 ⪢ directions of III–V compounds in a non-destructive way, which is very important for technological applications. A study of InAs growth suggests that one can have access to the III:V ratio on the surface using this technique. The occurrence of very large surface anisotropies (10% or more) related to the growth of lattice mismatched materials is reported.