Person: Olea Ariza, Javier
Universidad Complutense de Madrid
Faculty / Institute
Estructura de la Materia, Física Térmica y Electrónica
Now showing 1 - 10 of 55
- 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.
- PublicationEnergy levels distribution in supersaturated silicon with titanium for photovoltaic applications(American Institute of Physics, 2015-01) Pérez, E.; Castán, H.; García, H.; Dueñas, S.; Bailón, L.; Montero Álvarez, Daniel; García-Hernansanz, R.; García Hemme, Eric; Olea Ariza, Javier; González Díaz, GermánIn the attempt to form an intermediate band in the bandgap of silicon substrates to give it the capability to absorb infrared radiation, we studied the deep levels in supersaturated silicon with titanium. The technique used to characterize the energy levels was the thermal admittance spectroscopy. Our experimental results showed that in samples with titanium concentration just under Mott limit there was a relationship among the activation energy value and the capture cross section value. This relationship obeys to the well known Meyer-Neldel rule, which typically appears in processes involving multiple excitations, like carrier capture/emission in deep levels, and it is generally observed in disordered systems. The obtained characteristic Meyer-Neldel parameters were Tmn = 176 K and kTmn = 15 meV. The energy value could be associated to the typical energy of the phonons in the substrate. The almost perfect adjust of all experimental data to the same straight line provides further evidence of the validity of the Meyer Neldel rule, and may contribute to obtain a deeper insight on the ultimate meaning of this phenomenon. (C) 2015 AIP Publishing LLC.
- PublicationThermal stability of intermediate band behavior in Ti implanted Si(Elsevier Science BV, 2010-11) Mártil de la Plaza, Ignacio; González Díaz, Germán; Olea Ariza, JavierTi implantation in Si with very high doses has been performed. Subsequent Pulsed Laser Melting (PLM) annealing produces good crystalline lattice with electrical transport properties that are well explained by the Intermediate Band (IB) theory. Thermal stability of this new material is analyzed by means of isochronal annealing in thermodynamic equilibrium conditions at increasing temperature. A progressive deactivation of the IB behavior is shown during thermal annealing, and structural and electrical measurements are reported in order to find out the origin of this result.
- 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.
- PublicationTitanium doped silicon layers with very high concentration(American Institute of Physics, 2008-07-01) Mártil de la Plaza, Ignacio; González Díaz, Germán; Olea Ariza, JavierIon implantation of Ti into Si at high doses has been performed. After laser annealing the maximum average of substitutional Ti atoms is about 10(18) cm(-3). Hall effect measurements show n-type samples with mobility values of about 400 cm(2)/V s at room temperature. These results clearly indicate that Ti solid solubility limit in Si has been exceeded by far without the formation of a titanium silicide layer. This is a promising result toward obtaining of an intermediate band into Si that allows the design of a new generation of high efficiency solar cell using Ti implanted Si wafers.
- PublicationA detailed analysis of the energy levels configuration existing in the band gap of supersaturated silicon with titanium for photovoltaic applications(American Institute of Physics, 2015-12-28) Pérez, E.; Dueñas, S.; Castán, H.; García, H.; Bailón, L.; Montero, Daniel; García Hernansanz, Rodrigo; García Hemme, Eric; Olea Ariza, Javier; González Díaz, GermánThe energy levels created in supersaturated n-type silicon substrates with titanium implantation in the attempt to create an intermediate band in their band-gap are studied in detail. Two titanium ion implantation doses (1013 cm-2 and 1014 cm-2) are studied in this work by conductance transient technique and admittance spectroscopy. Conductance transients have been measured at temperatures of around 100 K. The particular shape of these transients is due to the formation of energy barriers in the conduction band, as a consequence of the band-gap narrowing induced by the high titanium concentration. Moreover, stationary admittance spectroscopy results suggest the existence of different energy level configuration, depending on the local titanium concentration. A continuum energy level band is formed when titanium concentration is over the Mott limit. On the other hand, when titanium concentration is lower than the Mott limit, but much higher than the donor impurity density, a quasi-continuum energy level distribution appears. Finally, a single deep center appears for low titanium concentration. At the n-type substrate, the experimental results obtained by means of thermal admittance spectroscopy at high reverse bias reveal the presence of single levels located at around Ec-425 and Ec-275 meV for implantation doses of 1013 cm2 and 1014 cm2, respectively. At low reverse bias voltage, quasi continuously distributed energy levels between the minimum of the conduction bands, Ec and Ec-450 meV, are obtained for both doses. Conductance transients detected at low temperatures reveal that the high impurity concentration induces a band gap narrowing which leads to the formation of a barrier in the conduction band. Besides, the relationship between the activation energy and the capture cross section values of all the energy levels fits very well to the Meyer-Neldel rule. As it is known, the Meyer Neldel rule typically appears in processes involving multiple excitations, like carrier capture and emission in deep levels, and it is generally observed in disordered systems. The obtained Meyer-Neldel energy value, 15.19 meV, is very close to the value obtained in multicrystalline silicon samples contaminated with iron (13.65 meV), meaning that this energy value could be associated to the phonons energy in this kind of substrates.
- PublicationSub-bandgap spectral photo-response analysis of Ti supersaturated Si(Amer Inst Physics, 2012-11-05) Mártil de la Plaza, Ignacio; García Hemme, Eric; García Hernansanz, Rodrigo; González Díaz, Germán; Olea Ariza, Javier; Prado Millán, Álvaro delWe have analyzed the increase of the sheet conductance (Delta G(square)) under spectral illumination in high dose Ti implanted Si samples subsequently processed by pulsed-laser melting. Samples with Ti concentration clearly above the insulator-metal transition limit show a remarkably high Delta G(square), even higher than that measured in a silicon reference sample. This increase in the Delta G(square) magnitude is contrary to the classic understanding of recombination centers action and supports the lifetime recovery predicted for concentrations of deep levels above the insulator-metal transition.
- PublicationLow-to-mid Al content (x~0-0.56) AlxIn1-xN layers deposited on Si(100) by RF sputtering(Wiley-VCH Verlag GmbH & Co. KGaA., 2020) Blasco, Rodrigo; Valdueza-Felip, Sirona; Montero, Daniel; Olea Ariza, Javier; Naranjo, Fernando BRadio frequency sputtering is a low-cost technique for the deposition of large-area single-phase AlInN on silicon layers with application in photovoltaic devices. Here we study the effect of the Al mole fraction x from 0 to 0.56 on the structural, morphological, electrical and optical properties of n-AlxIn1-xN layers deposited at 550ºC on p-Si(100) by radio frequency sputtering. X-ray diffraction data show a wurtzite structure oriented along the c-axis in all samples, where the full width at half maximum of the rocking curve around the InN (0002) diffraction peak decreases from ~9º to ~3º when incorporating Al to the AlInN layer. The root mean square surface roughness, estimated from atomic force microscopy, evolves from 20 nm for InN to 1.5 nm for Al0.56In0.44N. Low-temperature photoluminescence spectra show a blue shift of the emission energy from 1.59 eV (779 nm) for InN to 1.82 eV (681 nm) for Al0.35In0.65N accordingly to the Al content rise. Hall effect measurements of AlxIn1-xN (0 < x < 0.35) on sapphire samples grown simultaneously point a residual n-type carrier concentration in the 1021 cm-3 range. The developed n-AlInN/p-Si junctions present optimal material properties to explore their performance operating as solar cell devices.
- PublicationUV and visible Raman scattering of ultraheavily Ti implanted Si layers for intermediate band formation(Iop Publishing Ltd, 2011-11-09) Mártil de la Plaza, Ignacio; García Hemme, Eric; González Díaz, Germán; Olea Ariza, Javier; Prado Millán, Álvaro delWe assess the degree of crystallinity by means of UV and visible Raman scattering measurements of Ti implanted Si layers with very high doses (10(15)-5 x 10(16) cm(-2)) subsequently annealed by nanosecond pulsed laser melting (PLM). We obtain ultraheavily impurified Si layers with Ti concentrations six orders of magnitude above the solid solubility limit in a layer several tens of nanometers thick. The PLM annealing processes are needed to recover the crystal quality and to keep the high Ti concentration required to form an intermediate band (IB). The UV Raman analysis permits us to evaluate the lattice crystallinity of the different implanted doses probing only the implanted region and points out Ti interstitial location in the host lattice in agreement with theoretical predictions for IB formation. By contrast, visible Raman spectra are only sensitive to the presence of a fully amorphized implanted layer as in the rest of the crystalline layers the probing depth far exceeds the implanted layer thickness and the signal is dominated by the undamaged Si.
- PublicationElectrical characterization of amorphous silicon MIS-based structures for HIT solar cell applications(Springer, 2016-07-16) García, Héctor; Castán, Helena; Dueñas, Salvador; Bailón, Luis; García Hernansanz, Rodrigo; Olea Ariza, Javier; Prado Millán, Álvaro del; Mártil de la Plaza, IgnacioA complete electrical characterization of hydrogenated amorphous silicon layers (a-Si:H) deposited on crystalline silicon (c-Si) substrates by electron cyclotron resonance chemical vapor deposition (ECR-CVD) was carried out. These structures are of interest for photovoltaic applications. Different growth temperatures between 30 and 200 °C were used. A rapid thermal annealing in forming gas atmosphere at 200 °C during 10 min was applied after the metallization process. The evolution of interfacial state density with the deposition temperature indicates a better interface passivation at higher growth temperatures. However, in these cases, an important contribution of slow states is detected as well. Thus, using intermediate growth temperatures (100–150 °C) might be the best choice.