Cu2O/ZnO heterojunction was fabricated on
porous silicon
(PSi) by a two-step electrochemical deposition technique with changing
current densities and deposition times, and then the PSi/Cu2O/ZnO nanostructure was systematically investigated. SEM investigation
revealed that the morphologies of the ZnO nanostructures were significantly
affected by the applied current density but not those of Cu2O nanostructures. It was observed that with the increase of current
density from 0.1 to 0.9 mA/cm2, ZnO nanoparticles showed
more intense deposition on the surface. In addition, when the deposition
time increased from 10 to 80 min, at a constant current density, an
intense ZnO accumulation occured on Cu2O structures. XRD
analysis showed that both the polycrystallinity and the preferential
orientation of ZnO nanostructures change with the deposition time.
XRD analysis also revealed that Cu2O nanostructures are
mostly in the polycrystalline structure. Several strong Cu2O peaks were observed for less deposition times, but those peaks
diminish with increasing deposition time due to ZnO contents. According
to XPS analysis, extending the deposition time from 10 to 80 min,
the intensity of the Zn peaks increases, whereas the intensity of
the Cu peaks decreases, which is verified by the XRD and SEM investigations.
It was found from theI–Vanalysis that the PSi/Cu2O/ZnO samples exhibited rectifying
junction and acted as a characteristical p-n heterojunction. Among
the chosen experimental parameters, PSi/Cu2O/ZnO samples
obtained at 0.5 mA current density and 80 min deposition times have
the best junction quality and defect density.