Person: Pastor Pastor, David
Universidad Complutense de Madrid
Faculty / Institute
Física de Materiales
Now showing 1 - 10 of 15
- PublicationTransport mechanisms in hyperdoped silicon solar cells(Iop Publishing Ltd, 2022-12-01) García Hernansanz, Rodrigo; Duarte Cano, S.; Pérez Zenteno, Francisco José; Caudevilla Gutiérrez, Daniel; Algaidy, Sari; García Hemme, Eric; Olea Ariza, Javier; Pastor Pastor, David; Prado Millán, Álvaro del; San Andres Serrano, Enrique; Mártil de la Plaza, Ignacio; otros, ...According to intermediate band (IB) theory, it is possible to increase the efficiency of a solar cell by boosting its ability to absorb low-energy photons. In this study, we used a hyperdoped semiconductor approach for this theory to create a proof of concept of different silicon-based IB solar cells. Preliminary results show an increase in the external quantum efficiency (EQE) in the silicon sub-bandgap region. This result points to sub-bandgap absorption in silicon having not only a direct application in solar cells but also in other areas such as infrared photodetectors. To establish the transport mechanisms in the hyperdoped semiconductors within a solar cell, we measured the J-V characteristic at different temperatures. We carried out the measurements in both dark and illuminated conditions. To explain the behavior of the measurements, we proposed a new model with three elements for the IB solar cell. This model is similar to the classic two-diodes solar cell model but it is necessary to include a new limiting current element in series with one of the diodes. The proposed model is also compatible with an impurity band formation within silicon bandgap. At high temperatures, the distance between the IB and the n-type amorphous silicon conduction band is close enough and both bands are contacted. As the temperature decreases, the distance between the bands increases and therefore this process becomes more limiting.
- PublicationIndium tin oxide obtained by high pressure sputtering for emerging selective contacts in photovoltaic cells(Elsevier Science Ltd, 2022-01) Caudevilla Gutiérrez, Daniel; García Hemme, Eric; San Andres Serrano, Enrique; Pérez Zenteno, F.; Torres, I.; Barrio, R.; García Hernansanz, Rodrigo; Algaidy, Sari; Olea Ariza, Javier; Pastor Pastor, David; Prado Millán, Álvaro delThis article studies the physical and electrical behavior of indium tin oxide layers (ITO) grown by an unconventional technique: High Pressure Sputtering (HPS), from a ceramic ITO target in a pure Ar atmosphere. This technique has the potential to reduce plasma induced damage to the samples. The aim is to obtain, at low temperature via HPS, good quality transparent conductive oxide layers for experimental photovoltaic cells with emerging selective contacts such as transition metal oxides, alkaline metal fluorides, etc. We found that the resistivity of the films was strongly dependent on Ar pressure. To obtain device-quality resistivity without intentional heating during deposition a pressure higher than 1.0 mbar was needed. These films deposited on glass were amorphous, presented a high electron mobility (up to 45 cm2V- 1s- 1) and a high carrier density (2.9 x 1020 cm-3 for the sample with the highest mobility). The optimum Ar pressure range was found at 1.5-2.3 mbar. However, the resistivity degraded with a moderate annealing temperature in air. Finally, the feasibility of the integration with photovoltaic cells was assessed by depositing on Si substrates passivated by a-Si:H. The film deposited at 1.5 mbar was uniform and amorphous, and the carrier lifetime obtained was 1.22 ms with an implied open circuit voltage of 719 mV after a 215 degrees C air anneal. The antireflective properties of HPS ITO were also demonstrated. These results show that ITO deposited by HPS is adequate for the research of solar cells with emerging selective contacts.
- PublicationOn the Optoelectronic Mechanisms Ruling Ti-hyperdoped Si Photodiodes(Wiley, 2022-02) 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 Andres 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.
- PublicationCarrier Dynamics and Absorption Properties of Gold-Hyperdoped Germanium:Insight Into Tailoring Defect Energetics(Amer Physical Soc, 2021-06-23) Pastor Pastor, David; Dissanayake, Sashini Senali; Ferdous, Naheed; Gandhi, Hemi H.; Tran, Tuan T.; Williams, Jim S.; Aziz, Michael J.; Mazur, Eric; Ertekin, Elif; Sher, Meng-JuHyperdoping germanium with gold is a potential method to produce room-temperature shortwavelength-infrared radiation (SWIR; 1.4–3.0 μm) photodetection. We investigate the charge carrier dynamics, light absorption, and structural properties of gold-hyperdoped germanium (Ge:Au) fabricated with varying ion implantation and nanosecond pulsed laser melting conditions. Time-resolved terahertz spectroscopy (TRTS) measurements show that Ge:Au carrier lifetime is significantly higher than that in previously studied hyperdoped silicon systems. Furthermore, we find that lattice composition, sub-bandgap optical absorption, and carrier dynamics depend greatly on hyperdoping conditions. We use density functional theory (DFT) to model dopant distribution, electronic band structure, and optical absorption. These simulations help explain experimentally observed differences in optical and optoelectronic behavior across different samples. DFT modeling reveals that substitutional dopant incorporation has the lowest formation energy and leads to deep energy levels. In contrast, interstitial or dopant-vacancy complex incorporation yields shallower energy levels that do not contribute to sub-band-gap light absorption and have a small effect on charge carrier lifetimes. These results suggest that it is promising to tailor dopant incorporation sites of Ge:Au for SWIR photodetection applications.
- PublicationOvercoming the solid solubility limit of Te in Ge by ion implantation and pulsed laser melting recrystallization(IEEE, 2021) Caudevilla Gutiérrez, Daniel; Berencen, Y.; Algaidy, Sari; Zenteno Pérez, Francisco; Olea Ariza, Javier; San Andrés Serrano, Enrique; García Hernansanz, Rodrigo; del Prado Millán, Álvaro; Pastor Pastor, David; García Hemme, EricGermanium hyperdoped with deep level donors, such as tellurium, would lead to dopant-mediated sub-band gap mid-infrared photoresponse at room temperature. We use a combination of non-equilibrium techniques to supersaturate Ge with Te via ion implantation followed by pulsed laser melting (PLM). Typically, liquid N2 (77K) temperatures are used to avoid implantation-induced Ge surface porosity. In this work, alternatively, we report on the use of slightly higher implantation temperatures (143 K) together with an amorphous Si (a-Si) capping layer. We demonstrate that the solid solubility limit of Te in Ge is overcome upon recovering the crystallinity of the material after laser processing.
- PublicationHigh Pressure Sputtering of materials for selective contacts in emerging photovoltaic cells(IEEE, 2021-06) San Andres Serrano, Enrique; García Hernansanz, Rodrigo; Patricia Moreno, Gloria; García Hemme, Eric; Barrio, Rocío; Torres Almarza, Ignacio; Caudevilla Gutiérrez, Daniel; Pastor Pastor, David; Olea Ariza, Javier; del Prado Millán, Álvaro; Algaidy, Sari; Zenteno Pérez, FranciscoIn this work we have explored the growth by high pressure sputtering (HPS) of materials intended for novel selective contacts for photovoltaic cells. This technique shows promise for the low-damage low-temperature deposition of PV materials. We studied the deposition of ITO, MoOx and TiOx using pure Ar and mixed Ar/O2 atmospheres as well as ceramic or metallic targets. We show that HPS deposition of these materials is feasible. The growth rate is greatly reduced when oxygen is added to the argon sputtering atmosphere. The best sputtering RF power was 20-45 W for the pressure range studied. Finally, as-deposited films present high surface recombination, but a mild hot plate anneal at 200ºC recovers long effective lifetimes.
- PublicationGold-hyperdoped Germanium with Room-Temperature Sub-bandgap Optoelectronic Response(Amer Physical Soc, 2020-12-16) Gandhi, Hemi H.; Tran, Tuan T.; Kalchmair, S.; Pastor Pastor, David; Smilie, L. A.; Mailoa, Jonathan P.; Milazzo, Ruggero; Napolitani, Enrico; Loncar, Marco; Williams, James S.; Aziz, Michael J.; Mazur, EricHyperdoping germanium with gold is a potential method to produce room-temperature short-wavelength-infrared radiation (SWIR; 1.4–3.0μm) photodetection. We investigate the charge carrier dynamics, light absorption, and structural properties of gold-hyperdoped germanium (Ge:Au) fabricated with varying ion implantation and nanosecond pulsed laser melting conditions. Time-resolved terahertz spectroscopy (TRTS) measurements show that Ge:Au carrier lifetime is significantly higher than that in previously studied hyperdoped silicon systems. Furthermore, we find that lattice composition, sub-band-gap optical absorption, and carrier dynamics depend greatly on hyperdoping conditions. We use density functional theory (DFT) to model dopant distribution, electronic band structure, and optical absorption. These simulations help explain experimentally observed differences in optical and optoelectronic behavior across different samples. DFT modeling reveals that substitutional dopant incorporation has the lowest formation energy and leads to deep energy levels. In contrast, interstitial or dopant-vacancy complex incorporation yields shallower energy levels that do not contribute to sub-band-gap light absorption and have a small effect on charge carrier lifetimes. These results suggest that it is promising to tailor dopant incorporation sites of Ge:Au for SWIR photodetection applications.
- PublicationHigh-quality single-crystalline epitaxial regrowth on pulsed laser melting of Ti implanted GaAs(Elsevier Science Ltd, 2023-10-31) Algaidy, Sari; Caudevilla Gutiérrez, David; Perez Zenteno, F.; García Hernansanz, Rodrigo; García Hemme, Eric; Olea Ariza, Javier; San Andres Serrano, Enrique; Duarte Cano, S.; Siegel, J.; Gonzalo, J.; Pastor Pastor, David; Prado Millán, Álvaro delWe present a detailed investigation on the formation of supersaturated GaAs using Ti+ implantation followed by nanosecond Pulsed Laser Melting (PLM). We have synthesized high-crystal quality supersaturated GaAs layers with concentrations of Ti above the insulator to metal transition (Mott limit). The Ti-implanted concentration depth profiles after PLM obtained by Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) show a redistribution of Ti impurities within the first hundred nanometers and superficial concentration up to 1 × 1021 redistrcm-3. Raman spectroscopy of these Ti supersaturated, and regrown GaAs samples shows a sharp crystalline peak and tensile strain due to the Ti lattice incorporation. Scanning Transmission Electron Microscopy (STEM) and high-resolution Transmission Electron Microscopy (TEM) images show a good GaAs crystallinity after the PLM process. Energy-Dispersive X-ray Spectroscopy (EDS) reveals an enhanced Ti signal inside bubble-like structures and an appearance of interface oxide layer with all processed samples.
- PublicationExperimental verification of intermediate band formation on titanium-implanted silicon(American Institute of Physics, 2013-01-14) González Díaz, Germán; García Hemme, Eric; Olea Ariza, Javier; Pastor Pastor, David; Bailón, L.; Castán, H.; Dueñas, S.; García, H.; Pérez, E.Intermediate band formation on silicon layers for solar cell applications was achieved by titanium implantation and laser annealing. A two-layer heterogeneous system, formed by the implanted layer and by the un-implanted substrate, was formed. In this work, we present for the first time electrical characterization results which show that recombination is suppressed when the Ti concentration is high enough to overcome the Mott limit, in agreement with the intermediate band theory. Clear differences have been observed between samples implanted with doses under or over the Mott limit. Samples implanted under the Mott limit have capacitance values much lower than the un-implanted ones as corresponds to a highly doped semiconductor Schottky junction. However, when the Mott limit is surpassed, the samples have much higher capacitance, revealing that the intermediate band is formed. The capacitance increasing is due to the big amount of charge trapped at the intermediate band, even at low temperatures. Ti deep levels have been measured by admittance spectroscopy. These deep levels are located at energies which vary from 0.20 to 0.28 eV below the conduction band for implantation doses in the range 10(13)-10(14) at./cm(2). For doses over the Mott limit, the implanted atoms become nonrecombinant. Capacitance voltage transient technique measurements prove that the fabricated devices consist of two-layers, in which the implanted layer and the substrate behave as an n(+)/n junction.
- PublicationMeyer Neldel rule application to silicon supersaturated with transition metals(IOP Publishing Ltd, 2015-02-25) García Hemme, Eric; García Hernansanz, Rodrigo; Olea Ariza, Javier; Pastor Pastor, David; Prado Millán, Álvaro del; Mártil de la Plaza, Ignacio; González Díaz, GermánThis paper presents the results for the transverse conductance across a bilayer formed by supersaturating with diverse transition metals a thin layer of a silicon wafer. The layer is formed by ion implantation and annealed by pulsed laser melting. The transverse conductance is exponentially activated, obtaining values ranging from 0.018 to 0.7 eV for the activation energy and pre-exponential factors of 10^-2-10^12 S depending on the annealing energy density. A semi-logarithmic plot of the pre-exponential factor versus activation energy shows an almost perfect linear behavior as stated by the Meyer Neldel rule. The Meyer Neldel energy obtained for implantation with different transition metals and also annealed in different conditions is 22meV, which is within the range of silicon phonons, thus confirming the hypothesis of the Multi Excitation Entropy theory.