Thesis presented December 14, 2007

Abstract:
The work presented in this manuscript focuses on the structural (size, strain, defects, composition) investigation of Ge nano-islands grown on both nominal and pre-patterned Si(001) substrates by Molecular Beam Epitaxy, using grazing incidence (anomalous) X-ray diffraction and scattering at the European Synchrotron Radiation Facility (ESRF). The samples were either prepared in independent MBE chambers and then characterized ex situ on the ID01 ESRF beamline, or they were characterized in situ during their MBE growth, using the BM32 ESRF beamline setup. The dynamical scattering effects occurring in grazing incidence have been studied on the basis of finite element simulations of the strain fields in nano-islands, revealing the strong influence of the incident angle on the intensity scattered by large islands. A novel X-ray method has been developed to detect the presence of defects and to study the structure of their core by concentrating on measurements along rods of scattering by defects passing through bulk forbidden reflections. In order to obtain new insight into the dynamics of growth phenomena, the shape, size, growth mode, composition and possible defects and/or atomic ordering inside all islands were characterized, as a function of deposition, deposition temperature, flux and possible annealing. The evolution of strain, the transition from elastic to plastic relaxation, the intermixing and the correlation of these internal parameters with the different morphologies of the island have been addressed using in situ scattering methods. This study sheds light on the early transition to superdomes during a slow growth rate of Ge on Si(001) and reports a new shape of superdomes, which is the result of island coalescence.
At last, the growth on nominal Si(001) surfaces was compared to growth on Si(001) surfaces that were patterned according to different procedures: e-beam lithography or wafer bonding followed by chemical etching. It has been shown that by tuning the surface curvature, it is possible to change the relaxation state and the overall elastic energy of islands without modifying their mean Ge composition. These results show new insight about the intermixing process which does not appear to be strain-driven but induced by surface-mediated diffusion processes.

Keywords:
Strain, anomalous diffraction, grazing incidence X-ray diffraction and scattering, nano-islands, finite element simulations, defects, stacking faults, atomic ordering, implanted Si, lithography, intermixing, MBE, lateral organization, wafer bonding, pre-patterning, DAFS, DWBA

On-line thesis.