Beside growth, nanofabrication is achieved using shared facilities such as NEEL Nanofab and Grenoble PTA (for ICP etching). Regarding characterization, the group developed electrical characterization setups specifically adapted to diamond, such as Hall effect, current-voltage and capacitance measurements. For high power electrical measurements a specific platform, CARAPACE, is being developped in collaboration with G2ELab, with a LANEF support. For other analysis the group relies mainly on NEEL technical groups, in particular the POM technical group for microRaman, CL and FTIR spectroscopies, as well as optical profilometry.
Regarding growth, three reactors have been dedicated to diamond growth in a hydrogen/methane microwave plasma cavity. With these reactors, plasma working at medium pressure drives heating of gas phase by electrons allowing high surface temperature and reactive species creation. We also add diborane gas to dope the semiconductor up to metallic transition. However, to avoid cross contamination, each reactor is dedicated to specific studies. The most recently installed (2012) is devoted to low doped and thick diamond layers for power devices (Schottky diode) and was financed by the DiamondX2 project. Recently, we also developed in situ studies with the help of a spectroscopic ellipsometer. This optical device can be easily installed on reactors to measure in real time, the thickness, the roughness and in some cases the doping level. Diamond growth studies are consequently expanding into hitherto unexplored regimes, and a new approach to control the processes is being established.
The group has also a long-standing expertise of localised growth of carbon nanotubes, studied both for their interest in bio-sensors, see scientific achievement #2, but also for high resolution AFM tips. After a careful optimisation of the patented process, yielding batches of tips with a single or double-wall nanotube on their apex, the tips were sold as a commercial product by Nanoworld company. However, after a few years of production, the market was still too small to transfer this activity to a startup or to Nanoworld. This activity has been transfered to CNRS Bordeaux. The hot filament assisted CVD apparatus dedicated to nanotube growth has also been used for diamond etching by catalytic metallic particles such as Ni or Pd. For the fabrication of samples, specific diamond technology has been developed. Regarding lithography techniques, optical and laserbeam lithography on 3x3 mm2 samples has been developed and is used routinely. For diamond etching, a process has been developped using Inductively Coupled Plasma (ICP) Reactive Ion Etching. The receipes are now routinely used on PTA’s ICP machines. A new process based on catalytic etching has also been developped, see scientific achievement #2. Finally, for gate oxide ALD deposition was explored and optimized.
To assist the design of devices, or to understand electronic properties of specific structures, we developed a new simulation activity. The two main softwares used for such studies were Nextnano+ (developped by the Walter Schottky Institute, Germany) and SILVACO. Examples of our daily use of device simulations can be found in our references on delta-doped diamond, diamond MOS, pn junction core shell GaN wire… In the case of more complex systems, or systems where the atomic scale is relevant, ab initio calculations were perfomed by our colleagues from HYBRIDE, SIN or TMC teams, which led to common publications.
Finally the last important tools for our activities are the electrical and optical characterization. The main experimental techniques were Hall effect versus temperature (from 4K to 800 K), deep level transient spectroscopy (from 77K to 873 K) and impedance spectroscopy (from 77K to 873 K and from 500 Hz to 2 MHz), as well as I(V) characteristics under a controlled atmosphere. Combined with theoretical modeling, such experiments have been used in particular to describe the scattering processes which limit the mobility in boron doped diamond, to demonstrate the wrong assignement of a BH complex to a n-type dopant, or to identify new deep traps in diamond epilayers. Apart from the optical excitation/detection system included in our DLTS system, we developed ex situ ellipsometry so as to yield thin diamond epilayer thicknesses down to the nm-level.