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Seminario - XPS investigation of titanium contact formation to ZnO nanowires

Mercoledì 1 febbraio 2017 alle 14:00 nell'aula riunioni del Dipartimento di Ingegneria dell'Informazione in via Valotti 9 (II piano) si terrà il seminario dal titolo: "XPS investigation of titanium contact formation to ZnO nanowires" con Thierry Maffeis, College of Engineering, Swansea University, Bay Campus, Fabian Way, Crymlyn Burrows, Swansea, SA1 8EN, UK.


ZnO has received much attention over the past 15 years primarily because of its ability to grow into numerous nanostructures that have many potential applications in microelectronics, mechanical energy harvesting, sensors, field emitters ultra violet lasers, photovoltaics and other optoelectronic devices. All these devices require the formation of metal/ZnO contacts, the nature of which has profound influence on device performance, with Ohmic contacts preferred for most applications. For nanowire array style devices, where the nanowires grow quasi-vertically from a substrate, one electrical contact can often be made using the seed layer from which the nanowires are grown. To form a similar contact to the free ends of the nanowires, one requires metal deposition using techniques such a sputtering or evaporation. Au is commonly used in contact fabrication as it does not oxidise in air; however, a Schottky contact forms when it is deposited on ZnO. Therefore Ti is often used to form an initial Ohmic interface between the ZnO and Au due to its low work function. A drawback of this approach is that Ti is extremely reactive and oxygen atoms may out-diffuse from the ZnO into the Ti layer to form TiO2, which can cause a high contact resistance. Conversely, the formation of oxygen vacancies near the ZnO surface can increase carrier concentration and lower specific contact resistance. The TiO2/ZnO heterojunction is also of great importance for dye sensitised solar cells, photocatalysis, water-splitting and self-cleaning coatings. It is therefore important to understand the formation of the Ti/ZnO contacts and the TiO2/ZnO heterojunction in order to optimise device performances. Here, we controllably deposit Ti onto hydrothermally grown ZnO nanowires and investigate the formation of the metal-semiconductor contact using x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and scanning electron microscopy (SEM).

Mercoledì, 1 Febbraio, 2017