One-Step Formation of Plasmonic Cu Nanodomains in p-Type Cu$_2$O Matrix Films for Enhanced Photoconversion of n-ZnO/p-Cu$_2$O Heterojunctions

TL;DR

This study demonstrates the in-situ formation of plasmonic copper nanodomains within a Cu$_2$O matrix, enhancing photoconversion efficiency in heterojunction devices through controlled synthesis and characterization.

Contribution

It introduces a one-step reactive sputtering method to embed plasmonic Cu nanodomains in Cu$_2$O films, improving their optoelectronic properties for photoconversion applications.

Findings

Embedded Cu nanodomains exhibit surface plasmon resonance.

Bandgap of composites is reduced due to defect density.

Photocurrent density increases with plasmonic enhancement.

Abstract

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.