M. Cervera

On the true optical properties of zinc nitride

Refractive index (n) and extinction coefficient (k) of Zn3N2 layers deposited by radio-frequency magnetron sputtering at temperatures (Ts) between 298 and 523 K were determined by spectroscopic ellipsometry. Results showed strong variations of the apparent optical constants with Ts and time attributed to surface effects. Resonant Rutherford backscattering and spectroscopic ellipsometry confirmed the formation of a ZnO surface layer provoked by the ambient exposure. Samples grown at low Ts presented the lowest surface roughness and exhibited 2.0 < n < 2.8 and 0.6 < k < 1.0 in the 1.5–4.5 eV energy range. The extracted n and k values accurately reproduced the reflectance properties.

Thin Film Multiferroic Nanocomposites by Ion Implantation

Thin film multiferroic nanocomposites might enable a range of potentially disruptive integrated magnetoelectric devices for information storage, spintronics, microwave telecommunications, and magnetic sensing. With this aim, we have investigated ion implantation of magnetic species into ferroelectric single crystal targets as a radically novel approach to prepare film nanoparticulate magnetic-metal ferroelectric-oxide composites. These materials are an alternative to multiferroic oxide epitaxial columnar nanostructures that are under intensive research, but whose magnetoelectric response is far from expectations. Here, we unambiguously demonstrate the preparation of such a thin film multiferroic nanocomposite of Co and BaTiO3 by ion implantation of a high dose of the magnetic species, followed by rapid thermal processing under tailored conditions. Results thus constitute a proof of concept for the feasibility of obtaining the materials by this alternative approach. Ion implantation is a standard technique for the microelectronic industry in combination with well-established patterning procedures.

Amorphous CNx layers from neon electron cyclotron resonance plasmas with N2 and CH4 as precursors

© The Electrochemical Society, Inc. 2000. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS). The archival version of this work was published in Journal of The Electrochemical Society. Barbadillo, L., Hernandez, M. J., Cervera, M. and J. Piqueras. Amorphous CNx layers from neon electron cyclotron resonance plasmas with N2 and CH4 as precursors. Journal of The Electrochemical Society 147.10 (2000): 3864-3867

Scanning electron beam annealing of sputter-deposited titanium on silicon

Abstract Ti thin films sputter-deposited on single crystal Si wafers were annealed by using a scanning electron beam source. The resulting titanium silicides have been characterized by RBS and X-ray diffraction techniques. The experimental results show that the initial Ti layer thickness, in the studied range of 50 to 500 nm, does not affect the amount of formed silicide. RBS measurements are not enough to deduce the silicide composition due to the lack of well defined interfaces. X-ray measurements indicate the presence of only a single silicide phase, Ti5Si4. These results indicate that the interfaces in the structure Ti-silicide-Si, resulting from the e-beam treatment, are corrugated.

Cathodoluminescence from BN buried layers by high-dose ion implantation

Boron, nitrogen, and carbon ions were co-implanted in silicon wafers, and subsequently annealed. Infrared spectra show the formation of BN-rich buried layers. The presence of a band at 1375 cm−1 characteristic of boron nitride in a hexagonal configuration has been observed. Traces of the cubic phase formation were detected in some cases. Implanted samples exhibit a broad emission band about 550 nm.

Shallow buried SiNx layers

High dose nitrogen implantations have been performed at an energy of 30 keV. After high temperature annealing, 1200 °C, a buried layer composed mostly of silicon nitride is formed leaving an overlayer with a high fraction of crystalline silicon. The lattice constant of the overlayer and the region below the SiNx are reduced in 0.13% and 0.089%, respectively. The substitutional N seems to be responsible for this reduction.

Temperature evolution during scanning electron beam processing of silicon

Temperature profile evolutions produced by a scanning electron beam in crystalline silicon have been numerically calculated using a two-dimensional finite-element scheme. The temperature dependence of the different silicon properties as well as the electron penetration effects have been taken into account. Numerical calculations carried out at different conditions have been compared with experimental melting-threshold measurements using an electron beam with a Gaussian power density distribution. The good agreement between numerical calculations and experimental results proves the validity of the two-dimensional approach.

Fabrication and Characterization of Multiband Solar Cells Based on Highly Mismatched Alloys

Multiband solar cells are one type of third generation photovoltaic devices in which an increase of the power conversion efficiency is achieved through the absorption of low energy photons while preserving a large band gap that determines the open circuit voltage. The ability to absorb photons from different parts of the solar spectrum originates from the presence of an intermediate energy band located within the band gap of the material. This intermediate band, acting as a stepping stone allows the absorption of low energy photons to transfer electrons from the valence band to the conduction band by a sequential two photons absorption process. It has been demonstrated that highly mismatched alloys offer a potential to be used as a model material system for practical realization of multiband solar cells. Dilute nitride GaAs1-xNx highly mismatched alloy with low mole fraction of N is a prototypical multiband semiconductor with a well-defined intermediate band. Currently, we are using chemical beam epitaxy to synthesize dilute nitride highly mismatched alloys. The materials are characterized by a variety of structural and optical methods to optimize their properties for multiband photovoltaic devices.

Effect of the deposition temperature on the properties of Zn 3 N 2 layers grown by rf magnetron sputtering

In this work, polycrystalline zinc nitride films were prepared on Si and glass substrates by rf magnetron sputtering in N2 ambient using Zn as a target. Substrate temperature (Ts) was different for each deposition process ranging from 298 K to 523 K. Optical transmission experiments showed that the optical band gap of the resultant layers decreased as Ts increased. X-ray diffraction scans presented a pattern of oriented crystals along the (100) direction at low Ts in contrast to the highly disoriented patterns obtained at high Ts. Hall measurements were carried out and exhibited n-type character for all samples, with mobilities ranging between 10 and 30 cm2/Vs, and a resistivity reduction as substrate temperature increases. By scanning electron microscopy, it was possible to study the grain structure forming the surface of zinc nitride. The size of the grains became larger as Ts increased, which accounts for the reduction of the electrical resistivity.