Sergio Ferrero

Deep levels by proton and electron irradiation in 4H–SiC

The effects on 4H-silicon carbide epilayers of irradiation with protons and electrons having particle energies, respectively, of 6.5 and 8.2MeV were carefully studied and critically compared. In detail, the electronic levels associated with the irradiation-induced defects were analyzed by current-voltage characteristics and deep-level transient spectroscopy (DLTS) measurements up to 550K. In the same temperature range the apparent free-carrier concentration was measured by capacitance-voltage characteristics in order to monitor compensation effects due to the deep levels associated with the induced defects. Introduction rate, enthalpy, and capture cross section of such deep levels were compared. We found that a set of deep levels (at ET=0.39eV, ET=0.65eV, and ET=0.75eV) is the same in both cases of proton and electron irradiations, whereas two other pairs of levels (S1, ET=0.20eV and S1*, ET=0.23eV; S5, ET=1.09eV and S5*, ET=0.89eV) appearing in the same temperature range within the DLTS spectra should be...

Silicon resonant microcantilevers for absolute pressure measurement

This work is focused on the developing of silicon resonant microcantilevers for the measurement of the absolute pressure. The microcantilevers have been fabricated with a two-mask bulk micromachining process. The variation in resonance response of microcantilevers was investigated as a function of pressure (10−1–105Pa), both in terms of resonance frequency and quality factor. A theoretical description of the resonating microstructure is given according to different molecular and viscous regimes. Also a brief discussion on the different quality factors contributions is presented. Theoretical and experimental data show a very satisfying agreement. The microstructure behavior demonstrates a certain sensitivity over a six decade range and the potential evolution of an absolute pressure sensor working in the same range.

In situ MoS2 Decoration of Laser-Induced Graphene as Flexible Supercapacitor Electrodes

Herein, we are reporting a rapid one-pot synthesis of MoS2-decorated laser-induced graphene (MoS2-LIG) by direct writing of polyimide foils. By covering the polymer surface with a layer of MoS2 dispersion before processing, it is possible to obtain an in situ decoration of a porous graphene network during laser writing. The resulting material is a three-dimensional arrangement of agglomerated and wrinkled graphene flakes decorated by MoS2 nanosheets with good electrical properties and high surface area, suitable to be employed as electrodes for supercapacitors, enabling both electric double-layer and pseudo-capacitance behaviors. A deep investigation of the material properties has been performed to understand the chemical and physical characteristics of the hybrid MoS2-graphene-like material. Symmetric supercapacitors have been assembled in planar configuration exploiting the polymeric electrolyte; the resulting performances of the here-proposed material allow the prediction of the enormous potentialities of these flexible energy-storage devices for industrial-scale production.

Hydrogenated amorphous silicon carbon alloys for solar cells

Hydrogenated amorphous silicon carbon films were grown by PECVD from silane/methane gas mixtures by fixing the methane ratio in the gas phase and by changing the rf power and pressure. The effects of the discharge parameters on the optical, electrical and structural properties were investigated. These effects were attributed to the variation of carbon content in the film. The analyses enabled us to determine the optimal growth conditions to produce a-SiC:H materials, suitable in solar cell applications, with a good photosensitivity and low defect density of states.

SERS active silver nanoparticles synthesized by inkjet printing on mesoporous silicon

Inkjet printing technique is exploited for the synthesis of Ag nanoparticles (NPs) patterned on electrochemically etched silicon-based substrates. The nanostructure morphology, here analyzed by scanning electron microscopy, is dictated by the ink composition and the printing parameters. Under suitable excitation conditions, resonant surface-enhanced Raman scattering (SERS) performed on such metal-dielectric nanostructures can approach single-molecule detection as recently demonstrated on silvered porous silicon synthesized by immersion plating.PACS78.67.Bf; 78.30.-j

Defect characterization of 4H-SiC wafers for power electronic device applications

Silicon carbide is a semiconductor of choice for the fabrication of high-power, high-temperature and high-frequency electronic devices. Nevertheless, such a material still presents many problems as regards the crystallographic quality and the presence of defects, which influence the device performance. We have investigated 4H-SiC wafers and 4H-SiC epitaxial layers by microscopy and structural techniques in order to obtain information about the defect morphology. The goal of this analysis will be to correlate them with the electrical properties of SiC for power electronic device applications.

Growth and characterization of SiC layers obtained by microwave-CVD

Abstract Silicon carbide is a wide band gap semiconductor of interest for its application in many electronic devices. In recent years, a large research activity has been devoted to growth techniques for amorphous, polycrystalline or even epitaxial structures. In this paper, we have reported results on microcrystalline and polycrystalline SiC layers grown by high temperature ECR-CVD over 4″ (100) silicon wafer in SiH4+CH4 gas mixtures. The structure of the films has been investigated by X-ray diffractometry, micro-Raman spectroscopy and transmission electron microscopy (TEM). Stoichiometric SiC films containing a complete chemical order, 3C–SiC crystals with orientation close to that of Si substrate and lateral dimensions larger than 100 nm have been obtained.

Structural and optical properties of a-Si1−xCx:H grown by plasma enhanced CVD

Abstract In this work, we discuss on the physical properties of hydrogenated amorphous silicon carbide (a-Si 1− x C x :H) thin films deposited by plasma enhanced CVD by using SiH 4 +CH 4 and SiH 4 +C 2 H 2 gas mixtures under several deposition conditions. We can argue a complete chemical order in the samples deposited by SiH 4 +CH 4 for x >0.4, while for those grown by SiH 4 +C 2 H 2 , such order is preserved for lower C content. With regards to the radiative properties, for all the under-stoichiometric samples the photoluminescence (PL) Stokes shifts result to be strictly correlated to the absorption properties within the static disorder model. For C-rich materials, the electronic density of states becomes much more complex than in Si-rich ones because of the possibility of sp 2 and sp 3 configurations for C bonds, so that the presence of localized tail states cannot explain anymore the PL properties.

Properties of a-SiC:H films deposited in high power regime

Abstract The aim of the present paper is the study of the RF power effects on the properties of hydrogenated amorphous silicon-carbon (a-SiC:H) films, deposited in high power regime in a conventional plasma enhanced chemical vapor deposition system by using silane–methane gas mixtures highly diluted in hydrogen. Varying the RF power chemically ordered a-SiC:H alloys can be grown controlling the carbon content, C/[C+Si], and consequently the energy gap from 0.20 to 0.57 and 2.17 to 3.23 eV, respectively. C-rich films show defect density lower than 2×10 17 cm −3 and photoluminescence (PL) at room temperature. The PL peak position of the spectra shifts from 1.70 to 2.54 eV as the carbon content increases from 0.3 to 0.57.

4H-SiC Schottky Barrier Diodes Using Mo-, Ti- and Ni-Based Contacts

We have studied different Schottky and ohmic contacts on 4H-SiC with the aim to obtain Schottky barrier diodes (SBDs) capable to operate at high temperatures, frequencies and power densities for long periods of time, and showing low power losses. The control of the Schottky barrier plays an important role in minimizing the power loss of a SBD, and the metal-semiconductor interface properties strongly affect the overall performances of such a device. Schottky contacts were deposited using Ni, Ti, Ti/Al, Mo and Mo/Al layers, and the annealing treatments have been performed up to 600 °C using a rapid thermal annealing process (RTA). Ohmic contacts have been deposited on the wafer backside using Ti/Al or Ti/Ni/Ag layers. The Schottky diodes have been characterized by means of standard current-voltage (I-V) and capacitance-voltage (C-V) techniques. Schottky diodes with Mo and Mo/Al barriers show a lower barrier height and better overall performances in forward polarization when compared to the Ti- and Ni-based contacts.