Junction properties of single ZnO nanowires with asymmetrical Pt and Cu contacts

Abstract

Metal-semiconductor interfaces play a crucial role not only for regulating the electronic conduction mechanism but also in determining new functionalities in nanosized devices. In this work, we reported the investigation of the junction properties of single ZnO nanowires (NWs) asymmetrically contacted by means of a Pt electrochemically inert and a Cu electrochemically active electrode. At low applied voltages, these devices operate as diodes where the conduction mechanism was found to be dominated by the Schottky barrier at the Cu/ZnO interface. Junction parameters such as the Schottky barrier height, the ideality factor and the series resistance have been analyzed according to the thermionic emission theory. Different methods for parameter retrieval from I-V-T measurements are discussed and compared. A potential fluctuation model is considered in order to account for barrier inhomogeneities, revealing the presence of two Gaussian distribution of barrier heights. On the other hand, new device features arise from electrochemical dissolution and migration of Cu ions along the NW when high electric fields are implied. These electrochemical processes are underlaying the resistive switching and memristive behavior observed in single ZnO NWs, as suggested also by direct observation of Cu nanoclusters along the nanostructures after the switching events.

Water-Mediated Ionic Migration in Memristive Nanowires with a Tunable Resistive Switching Mechanism

“…Single NW memristive devices were realized by means of a combination of optical and electron beam lithography (EBL), as previously reported. , Initially, ZnO NWs were mechanically transferred from the growth substrate onto a SiO 2 insulating substrate that was pre-patterned with a probe circuit realized by optical lithography and Cr/Au deposition. Contact geometries to bring single isolated nanostructures into contact with the probe circuit were realized by means of EBL (FEI Quanta 3D Microscope) and subsequent metal deposition (thickness of 80 nm).…”

Quantum Conductance in Memristive Devices: Fundamentals, Developments, and Applications

“…[145] A particularly effective configuration of ECM employs a single-crystal semiconducting NW between an electromigrating electrode (Ag or Cu) and an inert electrode (Pt). [146,147] In this case, the low concentration of defects in the crystalline NW reduces the ionic transport in the bulk, so that the conductive bridge formation and rupture are localized on the NW surface (Figure 11a). In this way, the NW device acts as a resistive switching model system, where electronics and ionics are decoupled and all memristive functions-nonvolatile bipolar memory, multilevel switching, selector and synaptic operations imitating Ca 2+ dynamics of biological synapses-are exploitable.…”

TEM Nanostructural Investigation of Ag-Conductive Filaments in Polycrystalline ZnO-Based Resistive Switching Devices

“…The asymmetric I−V characteristic of the pristine state can be attributed to the junction properties with different metal work functions and chemical properties at Ag/ZnO and Pt/ZnO interfaces, as discussed in previous works. 15,39 To investigate the leakage current of the devices with different thicknesses of the matrix before electroforming, we have investigated the I−V characteristic in the pristine state in a small voltage range, as shown in Figure S4a. The Schottky behavior was observed even for the highest dose used for the creation of the perturbation and therefore the thinnest layer of the ZnO switching matrix, and this confirms that the insulator layer is still present.…”

“…In our case, according to Yang et al, the growth of the filament from the inert to the active electrode testifies the high mobility of Ag + species in the ZnO matrix. 26 During the device setting, heating by a Joule effect can locally lead to very high temperatures, as high as 800−900 K. 39,40 When high temperatures are reached, a reorganization of the material structure occurs and monocrystalline filaments can be created. To reset the device back to the OFF-state, an opposite voltage is applied, which leads to a dissolution of the conducting filament.…”