G. García Salgado

Bio: G. García Salgado is an academic researcher from Benemérita Universidad Autónoma de Puebla. The author has contributed to research in topics: Porous silicon & Silicon. The author has an hindex of 3, co-authored 12 publications receiving 75 citations.

Optical and Compositional Properties of SiO x Films Deposited by HFCVD: Effect of the Hydrogen Flow

Abstract: In this work, the effect of hydrogen flow and thermal annealing on the compositional and optical properties of non-stoichiometric silicon oxide (SiOx) films with embedded silicon nanocrystals is reported. The SiO x films are obtained by hot filament chemical vapor deposition technique at three different hydrogen flow levels, namely, 50 sccm, 100 sccm, and 150 sccm. The SiOx films are characterized by different techniques. It is found by x-ray photoelectron spectroscopy (XPS) that with increasing hydrogen flow, the SiOx films contain higher silicon (Si) concentration. When the hydrogen flow decreases, the absorption edge of the as-grown SiOx films, as obtained from the transmittance spectra, shifts from 300 nm to 500 nm, and this opens the possibility of band gap tuning. Increasing the hydrogen flow level in turn means that the SiOx films contain higher Si concentration, as confirmed by the XPS profile composition measured in the SiOx films. After thermal annealing, the SiOx films transmittance spectra showed a further shift of the absorption edge toward larger wavelengths. The Fourier transform infrared (FTIR) spectroscopy reveals film composition changes induced by the hydrogen flow variations. In addition, the FTIR spectra reveal the bands attributed to the hydrogen presence in the as-grown SiOx films. The bands become more intense with increasing hydrogen flow, but they rapidly disappear after the thermal annealing. The as-grown SiOx films exhibit wide band photoluminescence (PL) spectra with the main components at 688 nm, 750 nm, and 825 nm. The SiOx film deposited at 100 sccm hydrogen flow level shows the strongest PL intensity. According to PL results, the thermal annealing of the SiOx films generates the PL quenching in all samples due to hydrogen evaporation. The defects such as OH and Si–H groups in the as-grown SiOx films not only modify the optical band gap structure, but they also play the role of passivating non-radiative defects, which enhances the PL emission.

Influence of trapping and de-trapping charge in MOS-like structures with single and twofold SiOx films as active layers

Abstract: Single and twofold non-stoichiometric silicon oxide (SiOx) films are considered as an active layer in metal oxide semiconductor (MOS)-like structures. Such films were obtained by hot filament chemical vapor deposition (HFCVD) technique in the range of temperatures from 900 °C to 1150 °C. They were subjected to a thermal annealing at 1100 °C. In order to know their optical and electrical properties, their transmittance spectra, absorption coefficients, absorbance (FTIR) spectra, photoluminescence (PL) spectra, current–voltage (I–V) curves and capacitance–voltage (C–V) ones were obtained. The optical energy gap of twofold SiOx films as a function of the growth temperature (Tg), suffers non-linear variations in the range from 2.25 to 1.8 eV when we make combinations of different Tǵs in both films; besides, such films exhibit compositional changes when Tg is varied and a restructuration (phase separation) takes place because of thermal annealing. Light emission in single and twofold SiOx films is ascribed to both silicon nanocrystals (Si-ncs) and some kinds of defects, which are produced during the growth process and thermal annealing. In the case of twofold films it is observed that the effect of thermal annealing induces emission in the orange-near infrared range and in the violet-blue bands but without the presence of the green–yellow band. MOS-like structures using single and twofold films, show different electrical phenomena such as the influence of trapping and de-trapping charge. The influence of Si-ncs and defects gives place to spike and stair-like behaviour in I–V curves. Measurements of the electrical I–V and C–V curves are obtained under dark conditions.

Phase transition on CdSe thin films by changing the volume concentration of Se

Abstract: In this work CdSe thin films were grown by chemical bath deposition (CBD)6 onto glass substrate with approximately 2000 A thickness. The samples have been prepared by changing the volume concentration of the solution in the range of 5-45 ml. of Se, the other growth parameter such as reactive concentration an stirring remained constant during the growth process. The volume of the solution of Se was varied in order to perform the crystalline phase transformation from cubic zincblende (ZB) to the hexagonal wurtzite (W) structure. The change in the crystalline structure and electrical properties were noticeable, whereas the growth volume concentration was increased. The characterization of the samples included optical absorption, X ray diffraction, reflectivity electronic dispersive spectroscopy and dark electrical conductivity analyses. The optical absorption spectra allowed to calculate the energy band-gap (Eg) value and, hence, the evolution of Eg through the transformation from the cubic crystalline phase to the hexagonal phase. The X ray diffraction spectra also showed the complete microstructural transformation from cubic samples up to the entire hexagonal lattice for samples with higher volume of the solution of Se.

Polydiacetylene paper-based colorimetric sensor array for vapor phase detection and identification of volatile organic compounds

Abstract: Detection and identification of VOCs in their vapor phase is essential for safety and quality assessment. In this work, a novel platform of a paper-based polydiacetylene (PDA) colorimetric sensor array is prepared from eight diacetylene monomers, six of which are amphiphilic and the other two are bolaamphiphilic. To fabricate the sensors, monomers are coated onto a filter paper surface using the drop-casting technique and converted to PDAs by UV irradiation. The PDA sensors show solvent induced irreversible color transition upon exposure to VOC vapors. When combined into a sensing array, the color change pattern as measured by RGB values and statistically analyzed by principal component analysis (PCA) is capable of distinguishing 18 distinct VOCs in the vapor phase. The PCA score and loading plots also allow the reduction of the sensing elements in the array from eight to three PDAs that are capable of classifying 18 VOCs. Utilizing an array containing only two PDAs, various types of automotive fuels including gasoline, gasohol and diesel are successfully classified.

The potential of porous silicon gas sensors

Abstract: Recent developments in porous silicon gas sensors have been reviewed. Monitored species detection levels, and the mechanisms of sensing for different sensor designs are also discussed. Porous silicon surface modification methods have been employed for detecting different gas molecules; H2O, ethanol, methanol, isopropanol, COx, NOx, NH3, O2, H2, HCl, SO2, H2S and PH3.