The origin of opto-functional enhancement in ZnO/CuO nanoforest structure fabricated by submerged photosynthesis

Semiconductor hetero-nanostructures are of great interest for practical industry use. In this report, we demonstrated ZnO/CuO nanoforest (NFRs) fabricated by galvanic submerged photo-synthesis (G-SPSC) method, which utilizes light illumination in pure water without additives. For the first time, we elucidated the origin of its enhanced opto-functional properties. At the hetero-epitaxial interface, ZnO(001)/CuO(001) planes linkage were established, even though with 13.62 – 28.15% local lattice discrepancies along the c axis. Formed under Zn rich condition and photo-induced {110} ZnO surface, the NFRs exhibited photoluminescence emissions at 450 nm and 650 nm, due to zinc interstitial (IZn) and oxygen vacancies (VO). Ternary oxide of ZnCuO2 was discovered. The interface exhibited significant emission at 650 – 700 nm and absorbance at 450 – 500 nm. On the basis of STEM-VEELS spectra and ab initio calculations, electrons occupancy at Cu 3p was responsible for 2.0 eV peak of the interface absorption coefficient. In particular, an interface dipole under interface-induced gap states (IFIGS) was clarified, caused by quasi defects zinc antisite (ZnO). This led to an incommensurate charge density (ICCD) for a coherent ZnO(001)/CuO(001) interface. This is the origin for the opto-functional enhancement of the ZnO/CuO NFRs, where a maximum 12% IPCE at 550 nm, a 20% increase from similar NFRs morphology was demonstrated. Our results indicated a promising method and strategy for novel hetero-epitaxial nanostructures fabrication in the field of optoelectrical devices.