Piezoelectric-Potential-Controlled Polarity-Reversible Schottky Diodes and Switches of ZnO Wires

Abstract

Using a two-end bonded ZnO piezoelectric-fine-wire (PFW) (nanowire, microwire) on a flexible polymer substrate, the strain-induced change in I-V transport characteristic from symmetric to diode-type has been observed. This phenomenon is attributed to the asymmetric change in Schottky-barrier heights at both source and drain electrodes as caused by the strain-induced piezoelectric potential-drop along the PFW, which have been quantified using the thermionic emission-diffusion theory. A new piezotronic switch device with an "on" and "off" ratio of ∼120 has been demonstrated. This work demonstrates a novel approach for fabricating diodes and switches that rely on a strain governed piezoelectric-semiconductor coupling process.Binary switching is the principle of many electronic devices for applications such as data storage and logic circuits. Up to now most of the nanoscale switches are operated by an electrostatic force between a suspended carbon nanotube (CNTs)/nanowire and its counter electrode to switch between "on" and "off" depending on mechanical contact. [1][2][3] As the size of the devices reaching nanoscale, a small gap of ∼10 nm is required to be maintained between the CNTs/nanowire and the electrode for electro-mechanical switching. In such a case, the van der Waals interaction between the CNT and the electrode may be strong enough to bind the two together so that the device cannot perform the "off" function as required. Furthermore, the random thermal vibration at the tip of CNT may also become sufficiently large at conventional operating temperatures, which can strongly increase the device instability. 4 As a result, the reliability, lifetime and manufacturability of these devices are challenged.The Schottky barrier diode, a metal-semiconductor (MS) rectifying junction that generally exhibits switching effect, may overcome the drawbacks. ZnO, a material that exhibits semiconductor and piezoelectric properties, is likely a candidate for fabricating diode-based switching devices.Recently, various novel devices have been fabricated using ZnO nanowires/nanobelts by utilizing its coupled piezoelectric and semiconducting properties (piezotronic effect), such as nanogenerators, 5,6 piezoelectric field effect transistors and chemical sensors, 7,8 piezoelectric diodes, 9 triggers, 10 transducer and actuator, 11 and flexible piezotronic strain sensors. 12 In this letter, we report a new type flexible piezotronic switch device that is built using a single ZnO piezoelectric fine wire (PFW) (nanowire, microwire). Its operation mechanism relies on the piezoelectric potential induced asymmetric change in Schottky-barrier height (SBH) at the source and drain electrodes. The change of SBH is caused by the combined effects from strain-induced band structure change and piezoelectric potential. The device demonstrated here presents a new electromechanical switch built based on piezotronic effect. 13 For this study, the device was fabricated by bonding an ultralong ZnO PFW laterally on a polystyrene (PS) substrate,...

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“…Earlier in our work, we have used Au sputtered top electrode to work as schottky contact with ZnO nanowires but in this study we have explored the role of Pt sputtered electrode [8][9][10]. ZnO nanostructures also exhibit robust properties which make them promising candidate to be used in mechanicalelectrical energy conversion devices [11]. ZnO, due to its semiconducting and piezoelectric properties, it is considered highly favorable in UV lasering [12], UV sensors [13], light emitting diodes [14], gas sensors [15,16] and solar cells [17].…”

Power generation with laterally packaged piezoelectric fine wires

“…The free electrons can enter the PFW and screen the piezoelectric charges, reducing the local effective potentials to V 1 2 and V 1 þ , but the free electrons cannot completely neutralize/deplete the piezoelectric charges because the latter cannot move (Fig. 4g) 15,16 . This process continues until an electric potential due to the free moving electrons is created across the PFW to balance the piezoelectric potential and the Fermi levels at the two electrodes reach a new equilibrium value (Fig.…”

Design and tailoring of patterned ZnO nanostructures for energy conversion applications

“…Vertically aligned ZnO NAs have been widely used in NG devices, by virtue of the piezoelectric effect [149][150][151]. However, the screening effect on the piezoelectric field induced by the free carriers in ZnO seriously inhibited the output performance of ZnO NAsbased NGs [152][153][154][155].…”