Person: González Díaz, Germán
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First Name
Germán
Last Name
González Díaz
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Estructura de la Materia, Física Térmica y Electrónica
Area
Electrónica
Identifiers
49 results
Search Results
Now showing 1 - 10 of 49
Item Full composition range silicon oxynitride films deposited by ECR-PECVD at room temperature(Thin Solid Films, 1999) Mártil de la Plaza, Ignacio; González Díaz, Germán; Prado Millán, Álvaro delSilicon oxynitride films were deposited at room temperature using the ECR-PECVD technique. Precursor gases were O(2), N(2) and SiH(4). The composition of the films can be controlled by regulating the gases flow ratio. R = (O(2) + N(2))/SiH(4) and R' = O(2)/SiH(4) have proved to be the key deposition parameters. FTIR spectroscopy, AES and ellipsometric measurements were performed in order to characterise the films. A single Si-O/Si-N stretching band is observed in the FTIR spectrum for all compositions, indicating single-phase homogeneous SiO(x)N(y) films. FWHM of the stretching band shows a maximum for the composition corresponding to the same number of Si-O and Si-N bonds. Samples cover the whole composition range from silicon nitride to silicon oxide including nitrogen-rich films, even though the gas flow ratio R " = N(2)/O(2) during deposition was small (from R " = 1.0 for SiO(1.9)N(0.04) to R " I = 6.7 for SiO(0.26)N(1.2)). Silicon oxide composition samples (SiO(2.0)) show essentially the same TR features as the thermal oxide: Si-O stretching band located at 1072 cm(-1), with a FWHM of 96 cm(-1) and a shoulder/peak ratio of 0.30, while nitrogen-rich samples (SiO(0.26)N(1.2)) show a total bonded hydrogen content below 2 x 10(22) cm(-3).Item Strong subbandgap photoconductivity in GaP implanted withTi(Progress in Photovoltaics: Research and Applications, 2018) Olea Ariza, Javier; Prado Millán, Álvaro del; García Hemme, Eric; García Hernansanz, Rodrigo; Montero, Daniel; González Díaz, Germán; Gonzalo,, José; Siegel,, Jan; López,, EstherPhotovoltaic solar cells based on the intermediate band (IB) concept could greatly enhance theefficiency of future devices. We have analyzed the electrical and photoconductivity propertiesof GaP supersaturated with Ti to assess its suitability for IB solar cells. GaP:Ti was obtained byion implantation followed by pulsed‐laser melting (PLM) using an ArF excimer laser. It was foundthat PLM energy densities between 0.35 and 0.55 J/cm2produced a good recovery of thecrystalline structure of GaP (both unimplanted and implanted with Ti), as evidenced by highmobility measured values (close to the reference GaP). Outside this energy density window,the PLM failed to recover the crystalline structure producing a low mobility layer that iselectrically isolated from the substrate. Spectral photoconductivity measurements wereperformed by using the van der Pauw set up. For GaP:Ti a significant enhancement of theconductivity was observed when illuminating the sample with photon energies below 2.26 eV,suggesting that this photoconductivity is related to the presence of Ti in a concentration highenough to form an IB within the GaP bandgap. The position of the IB was estimated to be around1.1 eV from the conduction band or the valence band of GaP, which would lead to maximumtheoretical efficiencies of 25% to 35% for a selective absorption coefficients scenario and higherfor an overlapping scenarioItem A comparative study of anodic tantalum pentoxide and high-pressure sputtered titanium oxide(Journal of Materials Science: Materials in Electronics, 2003) Mártil de la Plaza, Ignacio; González Díaz, Germán; Prado Millán, Álvaro del; San Andrés Serrano, EnriqueIn this work we present a new method to fabricate improved TiO2 films by using a high-pressure sputtering system. In order to minimize the damage induced in the substrate surface by the ion bombardment, a high chamber pressure of 100 Pa is used, which is very much higher than typical values in conventional systems. We present results obtained by Xray diffraction and FTIR spectroscopy. Moreover, we will compare the properties of the resulting TiO2-insulator-metal capacitors with those of anodic Ta2O5. Very thin films of TiO2 have been obtained with a very promising quality for future electron device fabrication.Item Composition and optical properties of silicon oxynitride films deposited by electron cyclotron resonance(Vacuum, 2002) Mártil de la Plaza, Ignacio; González Díaz, Germán; Prado Millán, Álvaro del; San Andrés Serrano, EnriqueSilicon oxynitride films covering the whole composition range from silicon nitride to silicon oxide have been deposited by electron cyclotron resonance chemical vapor deposition from SiH4, O-2 and N-2 gas mixtures. The composition of the films has been determined by heavy-ion elastic recoil detection analysis (HI-ERDA), providing absolute concentrations of all elements, including H, and by Auger electron spectroscopy. Additionally, Fourier transform infrared (FTIR) spectroscopy and ellipsometry measurements have been performed on the same samples for optical characterization. The concentration of the different species (Si, O, N and H) and the density of the films have been calculated and compared to the theoretical values for stoichiometric films. The presence of N-H bonds and non-bonded H results in a significant decrease of the Si concentration with respect to the theoretical value, especially for samples close to silicon nitride composition. The decrease of the Si concentration results in a decrease of both the N and 0 concentrations. The overall result is a decrease of the density and therefore a decrease of the refractive index with respect to stoichiometric films. The total H content determined by ERDA has been compared with the area of the FTIR N-H stretching band, which is frequently used to obtain the H content. It has been found that the calibration factor for this band depends on composition, increasing with increasing the O content.Item The intermediate band approach in the third solar cell generation context(Proceedings of the 2013 Spanish Conference on Electron Devices, 2013) Mártil de la Plaza, Ignacio; García Hemme, Eric; García Hernansanz, Rodrigo; González Díaz, Germán; Olea Ariza, Javier; Prado Millán, Álvaro del; García, Héctor; Castán, HelenaWithin the framework of the third solar cell generation some new ideas to enlarge the spectral response of the solar cells toward the infrared have been proposed. Among them the inclusion of an Intermediate Band (IB) seems to be very promising. This paper will deal with one of the ways to generate the IB namely the deep level center approach. We will discuss not only its existence but also the carriers lifetime recovery which is necessary to obtain the expected increase of the solar cell efficiency.Item Bonding structure and hydrogen content in silicon nitride thin films deposited by the electron cyclotron resonance plasma method(Thin Solid Films, 2004) Mártil de la Plaza, Ignacio; González Díaz, Germán; Prado Millán, Álvaro del; San Andrés Serrano, EnriqueThe bonding structure and hydrogen content of amorphous hydrogenated silicon nitride (a-SiNx:H) thin films have been investigated by infrared spectroscopy and ion beam techniques. Electron cyclotron resonance plasma enhanced chemical vapor deposition was used to produce these films under different values of gas flow ratio, deposition temperature, and microwave power. The amount of bonded hydrogen was calculated from the N-H and Si-H infrared absorption bands. An increase of the SiH4 partial pressure during deposition was found to have the same effect on the H content as an increase of the substrate temperature: both cause a decrease of the N-H bond density and an increase in the number of Si-H bonds. This is explained by a competitive process in the formation of N-H and Si-H bonds during the growth of the film, whereby Si-H bonds are favored at the expense of N-H bonds when either the SiH4 flow or the substrate temperature are increased. Such tendency to chemical order is compared with previous results in which the same behavior was induced by thermal annealing or ion beam bombardment.Item Interfacial state density and conductance-transient three-dimensional profiling of disordered-induced gap states on metal insulator semiconductor capacitors fabricated from electron-cyclotron resonance plasma-enhanced chemical vapor deposited SiOxNyHz films(Japanese Journal of Applied Physics, 2003) Mártil de la Plaza, Ignacio; González Díaz, Germán; Prado Millán, Álvaro delAn electrical characterization of Al/SiOxNyHz/Si metal-insulator-semiconductor (MIS) structures has been carried out. SiOxNyHz films of different compositions have been obtained from these structures by varying gas flow in the electron-cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) system. The presence of nitrogen in the films increases the dielectric constant value and degrades the interface quality, as our measurements demonstrate. The effect of thermal annealing has also been determined. Capacitance-voltage (C-V) results show that unannealed samples exhibit positive flat-band voltages, whereas annealed ones exhibit negative values. On the other hand, from deep-level transient spectroscopy (DLTS) measurements we can conclude that interfacial state density diminishes when thermal treatments are applied. Moreover, conductance transient analysis provides the energetic and spatial distribution of defects in the films and demonstrates that thermal improvement affects not only the interface, but also the insulator bulk.Item Sub-bandgap absorption in Ti implanted Si over the Mott limit(Journal of Applied Physics, 2011) Mártil de la Plaza, Ignacio; González Díaz, Germán; Olea Ariza, Javier; Prado Millán, Álvaro delWe have analyzed the structural and optical properties of Si implanted with very high Ti doses and subsequently pulsed-laser melted (PLM). After PLM, all samples exhibit an abrupt and roughly uniform, box-shaped Ti profile, with a concentration around 2 x 10(20) cm(-3), which is well above the Mott limit, within a 150 nm thick layer. Samples PLM-annealed at the highest energy density (1.8 J/cm(2)) exhibit good lattice reconstruction. Independent of the annealing energy density, in all of the samples we observe strong sub-bandgap absorption, with absorption coefficient values between 4 x 10(3) and 10(4) cm(-1). These results are explained in terms of the formation of an intermediate band (IB) originated from the Ti deep levels.Item On the Optoelectronic Mechanisms Ruling Ti-hyperdoped Si Photodiodes(Advanced electronic materials, 2022) García Hemme, Eric; Caudevilla Gutiérrez, Daniel; Algaidy, Sari; Pérez Zenteno, Francisco José; García Hernansanz, Rodrigo; Olea Ariza, Javier; Pastor Pastor, David; Prado Millán, Álvaro del; San Andrés Serrano, Enrique; Mártil de la Plaza, Ignacio; González Díaz, GermánThis work deepens the understanding of the optoelectronic mechanisms ruling hyperdoped-based photodevices and shows the potential of Ti hyperdoped-Si as a fully complementary metal-oxide semiconductor compatible material for room-temperature infrared photodetection technologies. By the combination of ion implantation and laser-based methods, approximate to 20 nm thin hyperdoped single-crystal Si layers with a Ti concentration as high as 10(20) cm(-3) are obtained. The Ti hyperdoped Si/p-Si photodiode shows a room temperature rectification factor at +/- 1 V of 509. Analysis of the temperature-dependent current-voltage characteristics shows that the transport is dominated by two mechanisms: a tunnel mechanism at low bias and a recombination process in the space charge region at high bias. A room-temperature sub-bandgap external quantum efficiency (EQE) extending to 2.5 mu m wavelength is obtained. Temperature-dependent spectral photoresponse behavior reveals an increase of the EQE as the temperature decreases, showing a low-energy photoresponse edge at 0.45 eV and a high-energy photoresponse edge at 0.67 eV. Temperature behavior of the open-circuit voltage correlates with the high-energy photoresponse edge. A model is proposed to relate the optoelectronic mechanisms to sub-bandgap optical transitions involving an impurity band. This model is supported by numerical semiconductor device simulations using the SCAPS software.Item Ion Implantation and Pulsed Laser Melting Processing for the Development of an Intermediate Band Material(Ion Implantation Technology, 2012) Mártil de la Plaza, Ignacio; García Hemme, Eric; García Hernansanz, Rodrigo; González Díaz, Germán; Olea Ariza, Javier; Prado Millán, Álvaro delTi supersaturated Si layers with two different thicknesses have been obtained on the top of a Si substrate by means of ion implantation and pulsed laser melting processes. Time-of-flight Secondary Ion Mass spectrometry (ToF-SIMS) measurements show Ti concentration above the intermediate band formation limit. This feature has been obtained in 20 nm for one of the set of samples and in 120 nm in the other one. Sheet resistance measurements at variable temperature show an unusual electrical decoupling between the Ti implanted layer and the n-Si substrate in the two sets of samples. This behavior has been successfully explained using the intermediate band theory. These results points out that we have achieved thicker layers of intermediate band material.