Scientific direction Development of key enabling technologies
Transfer of knowledge to industry

PhD : selection by topics

Engineering science >> Solid state physics, surfaces and interfaces
2 proposition(s).

Epitaxial growth and nanosecond laser annealing of GeSn/SiGeSn heterostructures

Département Technologies Silicium (LETI)




Since 2015, CEA LETI has the capacity of depositing GeSn/SiGeSn heterostructures on 200 mm substrates. We are currently at the state-of-the-art in several of their application domains. In ordre to fabricate electically-pumped lasers able to operate at room temperature and performant Infra-Red photodetectors, we will explore during this PhD thesis the n-type and p-type doping of such layers, be it by ion implantation or in-situ during the epitaxial growth itself. In order to take full advantage of those doped layers, we will perform recristallisation and electrical activation anneals. With standard annealing techniques, we would be faced with the significant instability of GeSn / SiGeSn stacks (tin precipitation / surface segregation). This is why we will evaluate, during this PhD thesis, the interest of using nanosecond laser anneals and their impact on the structural and electrical properties of those stacks. Those studies, which will be conducted in our brand new SCREEN-LASSE LT3100 tool, will be among the first ever conducted on this type of semiconductors. We will notably focus on the evolution of cristalline quality, doping level, surface roughness, tin agglomeration / segregation and chemical content with the various process parameters (epitaxy and laser anneals). Such a know-how will be put to good use for the fabrication of innovative optoelectronics devices.

Silicon optomechanical nanoresonators pour DNA strands detection

Département Composants Silicium (LETI)

Laboratoire Composants Micro-Capteurs



The MEMS sensor laboratory at CEA LETI has a very strong expertise and an international recognition in the field of resonating MEMS/NEMS, and more recently for optomechanical resonators. The market of DNA sequencing has been exponentially growing and has reached impressive volumes for biomedical devices realized with micro- and nanotechnologies. The last sequencer generation dominating the market is based on fluorescence techniques. The requirement for external optical readout is an obstacle for faster analysis and miniaturization. Among several solutions investigated for sensing in liquid medium, the NEMS group at LETI recently performed a world first: a biological detection with an optomechanical resonator immersed in liquid. Beside extraordinary sensing performance, this technique allows a very local containment of light, and potentially a significant simplification of optical sequences. The PhD candidate will build on this know-how to study the identification of DNA pairs by a multi-parametric sensing technique: gravimetric on one hand (mass sensing by biological functionnalization), as well as optical. The PhD will study the possibility to monitor in real time and at the single DNA strand level the amplification of a DNA sequence by PCR. This will be done by taking into account field analysis constraints: portability, drastic reduction of analysis time, sample quantity to be analyzed, and thus reagent quantity. The candidate will have to contribute in all aspects, from design, fabrication to experimental proof of concept.

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