  Development of the new nanomaterial - the mesoporous Ge - by bipolar
electrochemical etching (BEE) and analysis of its physico-chemical properties
is the subject of this thesis. Formation of mesoporous Ge by electrochemical
etching was previously reported in the literature. However, up to now,
realization of thick (above 500 nm) mesoporous Ge layers with perfectly
controlled morphology has been an issue. Indeed, the physico-chemical
characterization of thin layers is much more complicated and the number of
possible applications is very limited. We have developed an electrochemical
model that describes the principal mechanisms of the pore formation which
allowed us to produce the thick (up to 10 um) mesoporous Ge structures with the
porosity adjustable in the range of 15% to 60% In addition, the formation of
porous nanostructures with well-controlled variable morphologies has now become
possible. Finally, the mastery of these parameters has opened the extremely
promising path towards realization of porous multilayer structures based on Ge
for many innovative and multidisciplinary applications. In particular, in the
context of this thesis, the mesoporous layers of Ge were optimized for
performing a layer transfer process of a triple-junction solar cell via a
sacrificial layer of porous Ge.
  Keywords: mesoporous Germanium, bipolar electrochemical etching,
electrochemistry of semiconductors, layer transfer process, solar cells.
