Defects, irradiation and related properties – DEFI


Modification and/or generation of new physical properties in materials can be achieved by defects, which can be introduced in a controlled way (concentration and type) using irradiation (and/or implantation). Irradiation is then a tool allowing to tune macroscopic properties. For micro-electronics, ionic implantation has become an essential tool for controlling electric properties of components by the introduction of dopants and deep levels (control of the lifetime of carriers). Defects can also aggregate to form "platelets" for instance (bidimensional defects of nanometer size, see Figure 1), which play an essential role for the fabrication of Silicon-On-Insulator devices. Furthermore, implantation can also be used in fundamental investigations, to improve the predictions regarding the behaviour of materials in use, such as in research made for developing the new generation of nuclear systems, or materials submitted to extreme conditions (highly damaged and high temperature). Implantation is also a tool for the synthesis of materials such as SiC-based Diluted Magnetic Semiconductors (DMS).

Our research themes essentially focus on the study of defects created by implantation/irradiation, their identification and their evolution in correlation with various macroscopic properties. These defects can also be created during the formation of germanide, which are used to create Schottky junctions for CMOS applications in germanium (sub-22 nm technology). 


    Fig.:

(a) High-Resolution Transmission Electronic Microscopy (HRTEM) image  of a (001) platelet formed by hydrogen implantation in germanium.

b) Structure of a (001) platelet including trapped H2 molecules. David et al, Phys. Rev. Lett. 102, 155504 (2009)

 

 

The investigation of formation and evolution mechanisms of defects (point defects, platelets, nano-cavities, {113} defects, etc.) is made essentially with experiments: capacitive spectroscopy, x-ray diffraction and transmission electronic microscopy. Numerical simulations  (ab initio, molecular dynamic) are also done together with experiments in order to bring complementary information, such as the fine structure of defects. For instance, the analysis of the contrast of high resolution images coupled with atomistic calculations has allowed us to determine the structure and the type of several kind of defects.

Simulations are also performed on model systems, for investigating elementary mechanisms such that the formation, creation and the annealing of defects (SiC under irradiation, stability and mobility of noble gas atoms in silicon and SiC). Developing interatomic potentials is also an activity of the research team.

 

Research topics:

Atomic structure of irradiation defects

Defects, irradiation and induced properties

Electrical characterization of irradiation defects








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