  To date, high efficiency multijunction solar cells have been developed on Ge
or GaAs substrates for space applications, and terrestrial applications are
hampered by high fabrication costs. In order to reduce this cost, we propose a
breakthrough technique of III-V compound heteroepitaxy on Si substrates without
generation of defects critical to PV applications. With this technique we
expect to achieve perfect integration of heterogeneous Ga1-xInxAs
micro-crystals on Si substrates. In this paper, we show that this is the case
for x=0. GaAs crystals were grown by Epitaxial Lateral Overgrowth on Si (100)
wafers covered with a thin SiO2 nanostructured layer. The cristallographic
structure of these crystals is analysed by MEB and TEM imaging. Micro-Raman and
Micro-Photomuminescence spectra of GaAs crystals grown with different
conditions are compared with those of a reference GaAs wafer in order to have
more insight on eventual local strains and their cristallinity. This work aims
at developping building blocks to further develop a GaAs/Si tandem demonstrator
with a potential conversion efficiency of 29.6% under AM1.5G spectrum without
concentration, as inferred from our realistic modeling. This paper shows that
Epitaxial Lateral Overgrowth has a very interesting potential to develop
multijunction solar cells on silicon approaching the today 30.3% world record
of a GaInP/GaAs tandem cell under the same illumination conditions, but on a
costlier substrate than silicon.
