Gökhan Utlu

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 the I-V analysis 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.

In this study, ZnO thin films, with thicknesses of 80-240 nm are prepared by thermal evaporation of ZnO pellets on glass substrates. Then, these films are annealed in air atmosphere at 300°C for 2 hours. ZnO formation has been investigated as a function of the film thickness. As deposited films appear to be brown since they are rich in Zn, whereas Zn phases are replaced by ZnO phases after annealing and the films show a transparent appearance. In thinner films (80-100 nm) the ZnO phases are not observed but Zn phase intensities decrease. Especially when the thickness is increased in 132-240 nm thick films, ZnO phases are observed after annealing, and their intensity is increased and polycrystalline structures are formed. XRD measurements show that Zn (002), Zn (100) and Zn (101) phases are present in our films before annealing. After annealing, the intensity of these zinc peaks decreases firstly due to the film thickness, and then at ZnO (100), ZnO (002) and ZnO (101) phases are formed. SEM, AFM analyzes show that ZnOs are formed in the form of nanorods on the surface and after these anneal the columnar growths occur and the particle diameters increase.

In this study, porous silicon (PS) samples were prepared on [Formula: see text]-type silicon (100) wafers by electrochemical etching method, varying the current density from 20 to 100[Formula: see text]mA/cm²and keeping constant HF concentration (10%) and etching time of 15[Formula: see text]min. Then, Ag thin films, which have 10, 50 and 100[Formula: see text]nm film thicknesses, were deposited on PS layers by using thermal evaporation to investigate the influence of Ag film thickness on structural and optical properties of PS. The structural and optical properties of PS and Ag deposited PS layers have been investigated by XRD, FE-SEM, Raman and photoluminescence (PL) spectroscopy. FE-SEM XRD and Raman analyzes indicate that average pore size and porosity of PS layers increase with the increasing current density. Further, Ag nanoparticles have embedded in pore channel. PL measurement reveals that higher porosity of PS would be better to form the Ag–PS nano-composite material leading to stronger PL band. The PL spectra of PS and Ag–PS samples indicate that PL bands show blue shift with increasing current density and film thickness. Consequently, it has been found that the structural and optical properties of PS depend on current density and Ag film thickness individually.