  Plasmonic Cu nanoparticles were in-situ grown into a Cu$_2$O semiconductor
matrix by using reactive magnetron sputtering and adjusting the amount of
oxygen available during the synthesis in order to prevent the oxidation of part
of copper atoms landed on the film surface. Varying only the oxygen flowrate
(OFR) and using a single Cu target it was possible to observe the evolution in
the simultaneous formation of metallic Cu and Cu$_2$O phases for oxygen-poor
conditions. Suchformation is accompanied by the development of the surface
plasmon band (SPB) corresponding to Cu, as evidenced by UV-Vis
spectrophotometry and spectroscopic ellipsometry. The bandgap values of the
elaborated composites containing embedded Cu plasmonic nanodomains were lower
than the bandgap of single-phased Cu$_2$O films, likely due to the higher
defect density associated to the nanocrystalline nature of films, promoted by
the presence of metallic Cu. The resistivity of the thin films increased with
more oxidative deposition conditions and was associated to an increase in
Cu$_2$O/Cu ratio and smaller and more isolated Cu particles, as evidenced by
high resolution transmission electron microscopy and X-ray diffraction.
Photoconversion devices based on the studied nanocomposites were characterized
by I-V and spectral photocurrent measurements, showing an increase in the
photocurrent density under light illumination as consequence of the plasmonic
particles excitation leading to hot carrier's injection in the nearby ZnO and
Cu$_2$O semiconductors.
