INFINOA   26585
INSTITUTO DE FISICA DEL NOROESTE ARGENTINO
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Novel Plasma Treatment over ZnO/MgO Core/Shell Nanostructures for the Enhancement of UV Exciton Emission
Autor/es:
VEGA, NADIA; STEREN LAURA; ZELAYA, PRISCILA; BONAPARTE, JUAN; TIRADO, MÓNICA; DI DONATO, ANDRÉS; COMEDI, DAVID
Lugar:
AVEIRO
Reunión:
Conferencia; 14th International Conference on Advanced Nano Materials, Topic: Nanomaterials; 2019
Institución organizadora:
UNIVERSIDAD DE AVEIRO-PORTUGAL
Resumen:
ZnO is a semiconductor with exceptional properties when compared to other direct band gap semiconductors, as it exhibits an exciton binding energy of ~60 meV and a band gap width in the UV of ~3.3 eV. These properties make ZnO usable for development ultraviolet (UV) optoelectronic devices [1]. Recently, great efforts were invested in the development of light emitting devices, sensors and lasers, using ZnO nanowires (NWs). However, due to the high surface-to-volume ratio, properties of ZnO NW ensambles are generally much more impacted by surface defects, such as oxygen vacancy and dangling bond, than those of bulk ZnO.To enhance the UV emission intensity, different materials have been proposed to act as NW surface passivating shells. The UV emission improvement in MgO shell passivated ZnO NWs was reported in recent years [1]. In this work, a plasma treatment over ZnO/MgO core/shell nanostructures was performed in order to remove portions of the MgO shell at the NW tips for electrical contacts.Surprisingly enough, after few minutes of exposure to the plasma, strong increases of the NW ultraviolet-to-visible emission intensity ratio were observed.EXPERIMENTAL STUDYZnO NWs were grown on p-type Si substrates by the hydrothermal method. In a second stage, conformal MgO coatings at two different thicknesses were grown on the NWs by vapour transport deposition. The obtained samples were irradiated for different times (1-16 min) with a 250 W Ar+ plasma in a reactive ion etching system operated at 250 V and 10 mTorr Ar pressure. The morphological characterization of the NWs was carried out by scanning electron microscopy (SEM). Photoluminescence (PL) spectroscopy measurements were performed at room temperature. RESULTS AND DISCUSSION A decrease in the average diameters of ZnO NWs coated with MgO was observed next to the NW tips after long plasma treatments. In the PL spectra, the UV excitonic emission intensity was found to increase with increasing plasma treatment time, with a concomitant reduction of the defect-related emission in the visible. A, maximum increase of the I[UV]/I[Vis] ratio by about a factor of 200 with respect to the unirradiated sample was observed after 10 min treatment, with the visible emission band almost disappearing from the PL spectra. SEM images revealed a gradual development of a pore network on the NW surfaces with increasing Ar+ plasma treatment time, indicating selective removal of material from the MgO shell.While these effects are currently being studied in more detail, it can be proposed that the energy deposited by the Ar+ ions during the plasma treatment promotes the annealing of metastable defects at the ZnO NW walls created during the ZnO/MgO core/shell growth steps. CONCLUSIONAr+ treatment of ZnO/MgO core/shell NWs grown by a two-step method combining the hydrothermal technique (ZnO) and vapour transport deposition (MgO) leads to an enhancement of the UV/vis emission intensity ratio by as much as a factor of 200. The effect could be due to energetic Ar+ ion bombardment induced removal of oxygen vacancies or other defects from the ZnO NWs walls, consequently eliminating recombination channels that compete with exciton recombinations. REFERENCE[1] N. Vega, et al. Nanotechnology, 28 (27) (2017) 275702