Papers by Author: Edwige Bano

Abstract: The until-now demonstrated SiC-Nanowire Field Effect Transistors (NWFETs) have exhibited poor performance due to the high residual doping of the NWs as well as the bad interface with the gate dielectrics. Top-down NWs have been used for the SiC NWFETs fabrication on the basis of low-doped 3C-SiC material and eliminating, thus, the first reason. The transistors with top-down grown NWs exhibited three orders of magnitude higher current and transconductance values with respect to SiC NWFETs with bottom-up grown NWs. Nevertheless, it was not possible to switch-off the transistors showing the importance of interface with the gate dielectrics.

Abstract: The fast and direct detection of small quantities of biomolecules improves early medical diagnosis of certain serious diseases as cancers and can be used to detect in situ the presence of pathogenic viruses or GMOs for food industry, protection environmental and bio-defense. Numerous research projects are conducted on nanoelectronic devices that can perform such detection with high sensitivity using nanostructures. Currently, these devices are made from Silicon nanowires [1]. For these applications, Silicon Carbide (SiC) material can advantageously replace Silicon as this semiconductor is now known to be biocompatible and to show a high chemical inertness [2]. Here, we present the electrical detection of DNA using a SiC Nanowire Field Effect Transistor (NWFET). The NWFETs are fabricated and then functionalized with DNA molecules. Between each step of the functionalization process, I-V characteristic measurements are performed. Comparative and simultaneous measurements are carried out on two SiC NWFETs: one is the sensor and the second one is used as a reference. Some interesting properties of the sensor are studied for the first time which opens the way to future developments of SiC nanowire based sensors.

Abstract: A comprehensive study on different polytypes (α-SiC and β-SiC) and crystal orientations ((0001) and (11-20) of 6H-SiC) has been investigated in order to elaborate Silicon carbide (SiC) nanopillar using inductively coupled plasma etching method. The SiC nanopillars with the cross section of rhombus, pentagon, and hexagonal have been obtained on β-SiC (001), misoriented α-SiC (11-20), and α-SiC (0001) on-axis substrates, respectively. It was found that crystal orientations and polytypes play key roles for the morphology of SiC nanopillars, which reflects the so-called Wulff's rule.

Abstract: Silicon nanowires obtained by a top-down approach have been carburized at high temperature and atmospheric pressure with two different gaseous precursors: CH4 and C3H8. These processes reveal core silicon / shell 3C-SiC nanowires. After being characterized by SEM, FIB-SEM and TEM microscopies, the 3C-SiC layer has been used as seed layer for the growth of epitaxial 3C-SiC on the nanowires. Preferential growth of 3C-SiC on the sidewalls of nanowires has been observed. Thanks to the biocompatibility of SiC compared to Si, this layer could act as a protective shell for biosensors based on Si nanowires transistor.

Abstract: We demonstrate a top-down fabrication technique for nanometer scale silicon carbide (SiC) pillars by using inductively coupled SF6/O2 plasma etching. The obtained SiC nanopillars exhibit high anisotropy features (aspect ratio ~ 6.5) with high etch depth (>7 μm). The etch characteristics of SiC nanopillars obtained under these conditions show a high etch rate (550 nm/min) and a high selectivity (over 60 for Ni mask). We obtained hexagonal symmetry of SiC nanopillar, which might be attributed to the crystallographic structure of the SiC phase.

Abstract: We present, for the first time, simulations of thermoelectric properties of silicon carbide (SiC) nanowires as a function of the wire cross section at high temperature (500K), based on non-equilibrium classical molecular dynamics simulations for the lattice thermal transport and non-equilibrium green's function for the electrical transport. Our calculations show that figure of merit (ZT) was increasing with decreasing cross section area: ZT of SiC nanowire at 2x2 nm2 has maximum value in the range of 0.65 - 0.89 at 500K, which is 7 - 8 times larger than maximum ZT of SiC thin film value (0.125 at 973 K). These results show that SiC may be a promising material for thermoelectric applications operating at high temperature.

Abstract: Carburization of silicon nanowires (NWs), with diameters of about 800 nm and lengths of about 10 µm, under methane at high temperature in order to obtain silicon carbide (SiC) nanostructures is reported here. The produced SiC nanostructures display a tubular shape and are polycrystalline. The as-prepared silicon carbide nanotubes (NTs) were characterized and studied by scanning electron microscopy (SEM), dual focused ion beam – scanning electron microscope (FIB-SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The formation of nanotubes can be explained by the out-diffusion of Si through the SiC during the carburization process.

Abstract: A top-down fabrication technique for nanometer scale silicon carbide (SiC) pillars has been demonstrated by using inductively coupled SF₆/O₂ plasma etching. At optimal etching conditions, the obtained SiC nanopillars exhibit high anisotropy features (aspect ratio ~ 6.5) with high etch depth (>7 μm). The etch characteristics of SiC nanopillars under these conditions show a high etch rate (550 nm/min) and a high selectivity (over 60 for Ni).

Abstract: Back-gated field effect transistors (FETs) based on 3C-SiC nanowire (NW) were fabricated and the electrical characterization revealed devices with either ohmic or rectifying contacts leading to two different operation modes. The transistors with ohmic-like contacts manifest very weak gating effect and the device switching off is not achievable even for high negative gate voltages due to the high electron concentration along the nanowires. In contrast, the devices with Schottky contact barrier at Source / Drain regions demonstrate a well determined switching off and in general better performance thanks to the modulation of the drain current through the control of Schottky barriers transparency at the source and drain regions. Nevertheless, ohmic contact devices are expected to demonstrate even better performance if the NW material quality as well as the quality of the interface with the gate oxide is substantially improved.

Abstract: Back-gated field effect transistors (FETs) based on catalyst-free grown 3C-SiC nanowire (NW) were fabricated. Devices with rectifying Source (S) and Drain (D) contacts have been observed. In contrast with the ohmic-like devices reported in the literature, the Schottky contact barrier (SB) at S/ D regions acts beneficially for the FET performance by suppressing the off-current. At high positive gate voltages (>10 V), the Schottky barriers tend to be more transparent leading to ION/IOFF ratio equal to ~ 103 in contrast to the weak gating effect of the ohmic-contacted 3C-SiC NWFETs.