JNTE 2017

French Symposium on Emerging Technologies for micro-nanofabrication / Journées Nationales sur les Technologies Emergentes en micronanofabrication.

Meet us at JNTE 2017 Orléans, France.

This workshop aims to bring together on an interdisciplinary basis all the major actors of the scientific community involved in the development of emerging technologies for micro-nanofabrication, with applications in the domains of optics and photonics, physics of nanostructures, electronics, chemistry, biology.

Our abstract “ZnO nanostructures for electronics : from transistors to nanogenerators” was accepted for oral presentation.

Event date : Nov. 20-22, 2017

New publication

C. Opoku, A. S. Dahiya, G. Poulin-Vittrant, N. Camara, D. Alquier, “Source-Gating Effect in Hydrothermally Grown ZnO Nanowire Transistors”, Physica Status Solidi A 213, No. 9 (2016) 2438–2445. Click here to read.

opoku_figure
(a) Scanning electron microscope image of a representative single ZnO NW device. (b) Schematic showing device cross-section. (c) Schematic showing the cross-sectional view of the depletion profile at source pinch-off.

Abstract

Nanowire source-gated field-effect transistors (NW SGT) are demonstrated using hydrothermally grown ZnO NWs. Device quality ZnO NWs with moderate n-type doping are achieved by thermal annealing in ambient air at ∼550 °C. A single ZnO NW device with Au source-drain contacts (s/d) is found to operate under source-gating mode, with characteristics markedly different from a reference device with ohmic contacts. The NW SGT shows exceptionally early drain current–voltage saturation (IDSAT–VDSAT) below 1 V. The change in saturation with the gate voltage (VG) is over 80 times lower than a reference device with ohmic contacts. This device behavior is attributed to the source-gate overlap, enabling gate field penetration inside the depleted source. Current modulation is obtained by a combination of gate-induced image force barrier lowering and the high internal electric fields at source pinch-off. Effective Schottky barrier heights are extracted from activation energy measurements, revealing systematic barrier lowering with increasing VG. These features of the device lead us to conclude that the single NW field-effect transistor (FET) with Schottky contacts operated under SGT mode.

New publication

E. G. Barbagiovanni, V. Strano, G. Franzò, R. Reitano, A. S. Dahiya, G. Poulin-Vittrant, D. Alquier, S. Mirabella, Universal model for defect-related visible luminescence in ZnO nanorods, RSC Advances 2016, RSC Adv. 6 (2016) 73170-73175. Click here to read.

barbagiovanni_figure

Abstract
We study the optical properties of ZnO nanorods (NRs) fabricated by chemical bath deposition, hydrothermal, and the vapour–liquid–solid method (VLS). Scanning electron microscopy demonstrates differences in the structural properties for the various samples. The optical emission properties are studied by photoluminescence (PL) spectroscopy where all samples are characterized by a UV and visible emission band. The visible emission band is due to defects in the nanorods. VLS samples show a blue shift in the visible region of the PL spectra with respect to the other samples, however, all three samples are fitted with the same three visible Gaussian components under varying percent contributions due to the structural differences. The visible defect components are characterized by blue (B), green (G), and orange (O) states with energies at 2.52 eV, 2.23 eV, and 2.03 eV, respectively. The applicability of this universal model for visible B–G–O defects is tested against the literature and successfully fitted regardless of the fabrication method. Differences in the percentage contribution for the visible B–G–O defects is explained by variations in the fabrication method. This model indicates how defects can be controlled based on the fabrication method. Furthermore, the B state, which is associated with the ‘green luminescence band’, results from a transition from the defect level to the valence band, or possibly a shallow-acceptor, according to photoluminescence excitation measurements. The role of the B state in sensing applications is discussed.