Single ZnO(core)/MgO(shell) nanowire: electrical properties in the dark and under illumination

GRINBLAT, GUSTAVO; BERN, FRANCIS; BARZOLA-QUIQUIA JOSÉ; ESQUINAZI, PABLO; TIRADO, MONICA; COMEDI, DAVID

TORINO

Simposio; 20th International Symposium on Metastable, Amorphous and Nanostructured Materials: ISMANAM 2013; 2013

ISMANAM y UNIVERSIDAD DE TORINO

Over recent years, much effort has been directed towards fabricating and manipulating ZnO based structures in the nanoscale due to their great potential applications in optoelectronic, electronic and sensing devices. In this work, we report on the fabrication and electrical properties of an individual ZnO/MgO (semiconductor core/isolator shell) nanowire (NW) characterized in the dark and under illumination in the 200-1100 nm wavelength range. ZnO NWs were grown on a Au-nanocluster covered silicon substrate through the Au-catalysed vapour transport and deposition method [1], using ZnO+graphite powder as precursor. For the MgO coating of ZnO NWs, a second step was performed where Mg shavings were used as the vapor precursor. Through EDS (electron dispersive spectroscopy), Zn, Mg and O were identified, while x-ray diffraction measurements revealed the presence of both oxides. Using a dry printing process, some of the NWs were transferred into a receiving insulating substrate (Si3N4/Si ), and then contacted with pairs of Cr/Au electrodes fabricated using electron beam litography and DC magnetron sputtering [see Fig. 1(a)].Figure 1: (a) SEM image of the contacted ZnO/MgO (core/shell) NW. The ZnO NW (core) diameter is 50 nm, while the total NW diameter is 150 nm. (b) I-V curves measured.The I-V curves (current vs. voltage) [Fig. 1(b)] reveal rectifying behavior in the dark, which is suppressed when illuminating (400 nm LED) due to the induced photocarriers. The asymmetric behavior is believed to be due to the presence of a MgO cap on top end of the NW, which is absent in the NW root. Such a novel MIS (metal-insulator-semiconductor)-type nanodevice exhibits a high diode ideality factor of 3.4 below 1 V (calculated from the I-V curve in the dark at forward bias), in agreement to that expected for MIS systems [2]. Furthermore, the NW photocurrent spectra show a large photoresponse in a wide wavelength range (230-960 nm), indicating its potential use as a convenient building block for nano-optoelectronic devices. [1]G. Grinblat, et al. Appl. Phys. Lett. 100 (2012), 233116.[2]S. Chand, et al. Physica B 390 (2007), 179?184.