Papers by Author: Giovanni Attolini

Abstract: We report on the synthesis of SiC nanowires (NWs) using iron as catalyst. The NWs were grown on silicon substrate by vapour-liquid-solid (VLS) mechanism with propane and silane as precursors, both 3% diluted in hydrogen, and hydrogen as carrier gas. The growth temperature was 1250°C, to reach the eutectic values of the Si-Fe alloy and to permit the VLS mechanism. The as-grown SiC nanowires were characterized by scanning and transmission electron microscopy. The nanowires are from 30 to 100 nm in diameter and several μm in length, with <111> growth direction.

Abstract: We describe a procedure for the optimization of a 3C-SiC buffer layer for the deposition of 3C-SiC on (001) Si substrates. A 100 – 150 nm thick SiC buffer was deposited after a standard carbonization at 1125 °C, while increasing the temperature from 1125 °C to 1380 °C. Ramp time influenced the quality and the crystallinity of the buffer layer and the presence of voids at the SiC/Si interface. After the optimization of the buffer, to demonstrate its effectiveness, a high-quality 3C-SiC was grown, with excellent surface morphology, crystallinity and low stress.

Abstract: 3C-SiC have been epitaxially grown through vapour phase expitaxy under a different grow conditions. Key electrical properties of these SiC layers have been characterised by fabrication and measurement of metal-SiC-metal devices. The electrical properties of SiC grown at different conditions have been analysed based on their structural and crystalline quality.

Abstract: 3C-SiC layers were grown on Si substrates using standard precursors (SiH₄ and C3H₈) and by adding methyl trichloro silane (MTS) to the gas phase, with growth temperatures between 1200 and 1300 °C. Characterization of the 3C-SiC layers shows that 3C-SiC grown with MTS has higher polycrystalline and amorphous content as well as lower residual stress.

Abstract: Surfaces of cubic silicon carbide (3C-SiC), grown by vapour phase epitaxy with silane and propane as precursors, were treated with plasma to remove residual species deposited during the growth procedure and the sample cooling down, or due to atmospherical contamination. The impurity traces were investigated with optical absorption spectroscopy. No morphology changes due to the plasma exposure were observed.

Abstract: Cubic silicon carbide - silicon dioxide core-shell nanowires have been synthesized in a thermal CVD system from carbon monoxide on silicon substrate. Using a non-ionic surfactant during the coating process of the substrate by the catalyst, the uniformity of the catalytic layer was improved, resulting in a more uniform nanowires growth. It is demonstrated that the core diameter is strongly correlated with the precursor concentration.

Abstract: In this work we report the enhancement of the 3C-SiC band edge luminescence induced by the SiO2 shell in SiC/SiO2 core/shell nanowires (NWs) system. We demonstrate that the shell enhances the SiC near band edge luminescence and we argue the formation of a type-I quantum well between the SiC core and the SiO2 shell, with the consequent injection of carriers from the larger band-gap shell to the narrower band-gap core.

Abstract: We have investigated 3C-SiC layers grown on silicon and on poli-Si in order to realize test MEMS structures. The strain of the films were investigated by the fabrication of cantilevers, beams, springs and we successfully fabricated a Double-Ended-Tuning-Fork double clamped SiC resonator on the film, with perfectly aligned actuation electrode.

Abstract: β-SiC/SiO₂ core-shell NWs have been synthesized on patterned silicon wafers in a CVD system, using carbon oxide as single precursor and nickel nitrate as catalytic element, in nitrogen or argon atmosphere at 1100°C. The coaxial structure and the crystallinity of the NW core are examined by (scanning) transmission electron microscopy. The patterning of the substrate allows to grow NWs in selected areas only, as imaged by SEM. Cathodoluminescence (CL) panchromatic images of the same areas point out that the light emitted under electron excitation is localized only in the area covered with NWs. The room-temperature CL spectrum has three different components peaked at 2.45 eV, related to the 3C-SiC near-band-edge emission, and at 2.75 and 3.75 eV, that are induced by the triplet and singlet states of oxygen-deficiency centers ODC(II) in silicon dioxide shell.

Abstract: In this work we report on the growth of cubic silicon carbide using CBr₄ and silane as precursors at different C₃H₈/CBr₄ flow ratios. The layers were deposited on 2’’ (001) Si wafers by means of the VPE technique in a horizontal cold-wall reactor with induction heating. The growths were performed at atmospheric pressure, in H₂ atmosphere and involved several steps: Si thermal etching; carburisation; epitaxial growth. Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were performed to observe the film morphology and defects and correlate them with the gas phase composition. Results show that the addition of CBr₄ to the standard SiH₄ and C₃H₈ precursor can change the crystalline nature and the morphology of the grown SiC.