Ion beam assisted processes
The principle of ion implantation is to bombard a target material with ions accelerated at high energy. This is a widely used technology in microelectronics for the localized doping of the semiconductors (e.g. for the formation of the P/N junctions). Ion implantation can also be used to introduce other chemical impurities in various substrates. This opens the possibility to synthesize new materials. At higher energy, the ion beams are also used to induce structural modifications or to develop specific analysis techniques.
Ion beam synthesis:
The subjects studied within this theme, targeting various applications, exploit the flexibility of ion implantation associated with the non-equilibrium character of the involved mechanisms and rely on an experimental ion beam facility covering a large range of energies (15 keV to 4 MeV). Our goal is to develop original processes, which can be easily transferred to the industry, for the fabrication of new nanostructures potentially useful for next generations of (opto)-electronic devices, particularly 3rd generation solar cells (in close connection with theme 1).
- Controlled growth of semiconducting nanocrystals:
-Doping of nanocrystals by co-implantation: Despite its interest for the realization of electronic devices, doping of nanocrystals (nc) turns out to be a difficult task because of their nanometer size. In our group, we study simultaneously the doping and the growth of nc's by co-implantation of silicon (and/or germanium) and of the usual dopant (As, P and B) into silicon oxide (or other dielectric) thin films. We study in detail the influence of the implantation and annealing conditions on the physical properties of the resulting nc's. This study is performed in close collaboration with theme 1, for its possible application in tandem solar cells.
-Integration of optoelectronic functions in Si technology: We study the ion beam synthesis of III-V nc's embedded in Si or SiOxNy by co-implantation of the group III and group V elements, as well as the performances of devices including such nc's. Some results exist in the literature concerning the ion beam synthesis of binary III-V nc's in Si and SiO2. However, these studies are only preliminary, and the growth of more complex nc's (ternary or even quaternary alloys) has never been investigated. The use of these ternary or quaternary alloys could open the way of a fine tuning of the optoelectronic properties, by controlling independently the band gap width and the lattice parameter (i.e. the coherence of the nc's with its environment). The targeted applications include optoelectronic devices fully compatible with the Si technology, as well as 3rd generation solar cells.
- Growth of graphene films by C implantation and diffusion in metallic matrixes:
We study an original route for the growth of controlled graphene film, using the mature ion implantation technology. In this process, the feasibility of which has already been proven, carbon is implanted in a diffusing metallic matrix (Ni, Cu, Ru), and then its segregation is induced by a high temperature anneal (possibly during the implantation itself). Depending on the detailed experimental conditions, it is foreseen to be able to induce the graphene film growth either at the surface of the metallic film or at the metal/substrate interface. This new method offers several advantages, as compared with the usual CVD method: i) precise and uniform control of the C implantation dose; ii) possibility to dope the graphene film by co-implantation of C and of the dopant; iii) selective growth at the metal/substrate interface by adapting the implantation energy and the carbon diffusivity (choice of the metal and of the anneal temperature); iv) easy integration in real electronic devices, since this technique uses a standard tool of the microelectronic. This research is performed in collaboration with the LPICM laboratory.
Structural modifications and analysis:
We contribute to various projects requiring ion beam related technologies or analysis. For example:
- Characterization of the metallic contamination in photovoltaic silicon wafers obtained by a new molding technique (French ANR project "MOSAIQUE", collaboration with CEA-Ines)
- Exfoliation of monocrystalline diamond for the fabrication of large area substrates for particles detectors (French ANR project "MONODIAM-HE", collaboration with IPHC-DRS)