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
44 results
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Now showing 1 - 10 of 44
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 scenario- Project number: 283
Item Integración de la formación teórica y experimental en el área de la Electrónica mediante el desarrollo de una plataforma de demostración del comportamiento real de los circuitos desarrollados en la docencia teórica(2020) San Andrés Serrano, Enrique; González Díaz, Germán; Del Prado Millán, Álvaro; Olea Ariza, Javier; Caudevilla Gutiérrez, Daniel; Herrera Fernández, Fernando; Paz López, Antonio Item Electronic transport properties of Ti-impurity band in Si(Journal of Physics D-Applied Physics, 2009) Mártil de la Plaza, Ignacio; González Díaz, Germán; Olea Ariza, JavierIn this paper we show that pulsed laser melted high dose implantation of Ti in Si, above the Mott transition, produces an impurity band (IB) in this semiconductor. Using the van der Pauw method and Hall effect measurements we find strong laminated conductivity at the implanted layer and a temperature dependent decoupling between the Ti implanted layer (TIL) and the substrate. The conduction mechanism from the TIL to the substrate shows blocking characteristics that could be well explained through IB theory. Using the ATLAS code we can estimate the energetic position of the IB at 0.36 eV from the conduction band, the density of holes in this band which is closely related to the Ti atomic density and the hole mobility in this band. Band diagrams of the structure at low and high temperatures are also simulated in the ATLAS framework. The simulation obtained is fully coherent with experimental results.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 Insulator-to-metal transition in vanadium supersaturated silicon: variable-range hopping and Kondo effect signatures(Journal of physics D: applied physics, 2016) García Hemme, Eric; Montero Álvarez, Daniel; García Hernansanz, Rodrigo; Olea Ariza, Javier; Mártil de la Plaza, Ignacio; González Díaz, GermánWe report the observation of the insulator-to-metal transition in crystalline silicon samples supersaturated with vanadium. Ion implantation followed by pulsed laser melting and rapid resolidification produce high quality single-crystalline silicon samples with vanadium concentrations that exceed equilibrium values in more than 5 orders of magnitude. Temperature-dependent analysis of the conductivity and Hall mobility values for temperatures from 10K to 300K indicate that a transition from an insulating to a metallic phase is obtained at a vanadium concentration between 1.1 × 10^(20) and 1.3 × 10^(21) cm^(−3) . Samples in the insulating phase present a variable-range hopping transport mechanism with a Coulomb gap at the Fermi energy level. Electron wave function localization length increases from 61 to 82 nm as the vanadium concentration increases in the films, supporting the theory of impurity band merging from delocalization of levels states. On the metallic phase, electronic transport present a dispersion mechanism related with the Kondo effect, suggesting the presence of local magnetic moments in the vanadium supersaturated silicon material.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.- Project number: 69
Item Mejora de las Metodologías Docentes para el área de la Electrónica(2018) San Andrés Serrano, Enrique; González Díaz, Germán; Mártil de la Plaza, Ignacio; del Prado Millán, Álvaro; García Hemme, Eric; Pastor Pastor, David; Olea Ariza, Javier; Lucía Mulas, María Luisa; Franco Peláez, Francisco Javier; Sánchez Balmaseda, Margarita Item Ruling out the impact of defects on the below band gap photoconductivity of Ti supersaturated Si(Journal of Applied Physics, 2013) Mártil de la Plaza, Ignacio; García Hemme, Eric; García Hernansanz, Rodrigo; González Díaz, Germán; Olea Ariza, Javier; Prado Millán, Álvaro delIn this study, we present a structural and optoelectronic characterization of high dose Ti implanted Si subsequently pulsed-laser melted (Ti supersaturated Si). Time-of-flight secondary ion mass spectrometry analysis reveals that the theoretical Mott limit has been surpassed after the laser process and transmission electron microscopy images show a good lattice reconstruction. Optical characterization shows strong sub-band gap absorption related to the high Ti concentration. Photoconductivity measurements show that Ti supersaturated Si presents spectral response orders of magnitude higher than unimplanted Si at energies below the band gap. We conclude that the observed below band gap photoconductivity cannot be attributed to structural defects produced by the fabrication processes and suggest that both absorption coefficient of the new material and lifetime of photoexcited carriers have been enhanced due to the presence of a high Ti concentration. This remarkable result proves that Ti supersaturated Si is a promising material for both infrared detectors and high efficiency photovoltaic devices.