Thesis presented October 04, 2006

Abstract:
The works presented in this manuscipt focus on the structural (size, strain, composition) investigation of GaN/AlN quantum dots, by means of x-ray spectroscopy in diffraction condition and x-ray anomalous diffraction and scattering. Those works are associated to Reflection High-Energy Electron Diffraction (RHEED), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and Medium-Energy Ion Scattering (MEIS) measurements. The measurement of fine structure oscillation in diffraction condition (x-ray spectroscopy in diffraction condition) and anomalous diffraction, using a grazing incidence setup, which is necessary for the study of nanoobjects, promoted specific experimental developments. Together with those developments, efforts were undertaken to properly take into account dynamical effects occuring in grazing incidence, for the quantitative analysis of the experimental results. Moreover, experimental results were compared with simulations of x-ray diffraction diagrams, fine structure signal in diffraction condition and anomalous diffraction spectrum, performed on the basis of simulations of the strain fields in the quantum dots.
The capping of (0001) GaN quantum dots by AlN, which is supposed to modifiy noticeably the structural and therefore optoelectronic properties of the dots, was studied in situ during growth and ex situ, by anomalous diffraction, x-ray spectrocopy in diffraction and absorption conditions, by TEM and AFM. Those studies put in evidence a pecular capping mecanism, and the evolution of the quantum dots structural properties. The stacking of GaN quantum dots planes, and the associated vertical correlation effects of the dots, were also analyzed in situ by anomalous diffraction and grazing incidence small angle scattering. Using RHEED as a tool to monitor the overall strain in the dots, a prelimianry analysis of the (0001) GaN quantum dots ripening under vacuum was carried out. At last, AFM, TEM and MEIS allowed to investigate the structural and optoelectronic properties of self-organized (11-20) GaN quantum dots.

Keywords:
quantum dots, X-ray spectroscopy, anomalous diffraction, strain

On-line thesis.