L. Bailon

Universidad de Valladolid, Valladolid, Castille and León, Spain

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Publications (65)71.47 Total impact

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    ABSTRACT: 2 MeV electron irradiation effects on the electrical properties of Al2O3 and HfO2-based metal–insulator–semiconductor capacitors have been studied. High-k dielectrics were directly grown on silicon by atomic layer deposition. Capacitors were exposed to three different electron irradiation doses of 0.025, 0.25 and 2.5 MGy. Capacitance–voltage, deep-level transient spectroscopy, conductance transients, flat-band voltage transients and current–voltage techniques were used to characterize the defects induced or activated by irradiation on the dielectric bulk and on the interface with silicon substrate. In all cases, positive charge is trapped in the dielectric bulk after irradiation indicating the existence of hole traps in the dielectric. When the samples are exposed to 2 MeV electron beam (e-beam) irradiation, electron–hole pairs are created and holes are then captured by the hole traps. Insulator/semiconductor interface quality slightly improves for low irradiation doses, but it is degraded for high doses. Irradiation always degrades the dielectric layers in terms of gate leakage current: the trapped holes are mobile charge which can contribute to leakage current by hopping from trap to trap.
    Thin Solid Films 05/2013; 534:482–487. · 1.87 Impact Factor
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    ABSTRACT: Metal–insulator–metal (MIM) capacitors were grown by atomic layer deposition using tBuN = Nb(NEt2)3 and ozone as niobium and oxygen precursors, respectively. Three different deposition temperatures were used and some of the films were postdeposition annealed. The permittivity values obtained reached a value of about 50 for the films crystallized after annealing at temperatures higher than 500 °C. However, the leakage current values for the crystalline films were higher than those in the case of amorphous films.
    Semiconductor Science and Technology 04/2013; 28(5):055005. · 1.92 Impact Factor
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    ABSTRACT: Defects on mono-like and polycrystalline silicon solar cells are studied in depth. These defects are in the basis of the higher quantum efficiency of mono-like solar cells (∼18%) with respect to polycrystalline ones (∼16%). Using the thermal admittance spectroscopy technique we found that both of them have a deep level due to a Fe-B complex. Furthermore, the deep level in the first one (224meV) is shallower than in the second one (345meV). Shallower deep levels degrade less the efficiency on solar cells, so this characteristic of the deep level in the mono-like solar cells leads to a better results in efficiency.
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    ABSTRACT: 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. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4774241]
    Journal of Applied Physics 01/2013; 113(2). · 2.21 Impact Factor
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    ABSTRACT: In order to find the regions in solar cells where the efficiency drops an experimental setup is tuned up. Through this equipment a set of samples are characterized checking that its response is the expected. The photocurrent maps obtained allow us to determine the regions with higher defects concentration. These regions will be characterized using electrical techniques which will give us additional information of the nature of these defects.
    Electron Devices (CDE), 2013 Spanish Conference on; 01/2013
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    ABSTRACT: The performance of commercial solar cells is strongly controlled by the impurities and defects present in the substrates. Defects induce deep energy levels in the semiconductor bandgap, which degrade the carrier lifetime and quantum efficiency of solar cells. A comprehensive knowledge of the properties of defects require electrical characterization techniques providing information about the defect concentration, spatial distribution and physical origin. The experimental techniques available in our laboratory are described in this work. In contrast, the efficiency of single junction solar cells can be drastically improved by the formation of an intermediate band in the midgap of a semiconductor. The intermediate band can be created from deep level defects if their concentration is high enough. Experimental results proving the intermediate band formation are also presented in this work.
    Electron Devices (CDE), 2013 Spanish Conference on; 01/2013
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    ABSTRACT: In this work, the results of the electrical behavior of metal-insulator-semiconductor (MIS) structures using Al <sub>2</sub> O <sub>3</sub> , HfO <sub>2</sub> , and nanolaminated layers as gate insulators are reported. The MIS structures were deposited by atomic layer deposition on several Si substrates. The authors observed different conduction mechanisms for these high- k based MIS structures depending on the bias regime. Direct tunneling, Fowler–Nordheim, Poole–Frenkel emission, and a negative resistance region have been observed at different gate voltage values. The tunneling conduction of majority and minority carriers assisted by defects located at the Al <sub>2</sub> O <sub>3</sub>/ HfO <sub>2</sub> and Al <sub>2</sub> O <sub>3</sub>/ metal interfaces can explain the negative resistance behavior observed in Al <sub>2</sub> O <sub>3</sub> and nanolaminated samples. In addition to current-voltage (I-V) measurements, MIS structures were also electrically characterized using capacitance-voltage (C-V) , deep level transient spectroscopy, conductance transients (G-t) , and flat-band voltage transient (V<sub> FB </sub>-t) techniques.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 02/2011; · 1.36 Impact Factor
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    ABSTRACT: SrTiO <sub>3</sub> thin films were grown to thicknesses in the range of 18–30 nm by atomic layer deposition using Sr (<sup>i</sup> P r <sub>3</sub> Cp )<sub>2</sub> and ( CpMe <sub>5</sub>) Ti ( OMe )<sub>3</sub> as strontium and titanium precursors at 250 and 300 ° C . Water or ozone was used as oxygen precursor. The films were amorphous in as-deposited state, but crystallized as cubic SrTiO <sub>3</sub> after annealing at 650 ° C . The highest permittivity values, 60–65, were achieved in the films deposited with ozone at 300 ° C . The films grown at 250 ° C tended to possess markedly lower leakage currents than those grown at 300 ° C .
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 02/2011; · 1.36 Impact Factor
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    ABSTRACT: Al/ScOx/SiNx/n-Si and Al/ScOx/SiOx/n-Si metal–insulator–semiconductor capacitors have been electrically characterized. Scandium oxide was grown by high-pressure sputtering on different substrates to study the dielectric/insulator interface quality. The substrates were silicon nitride and native silicon oxide. The use of a silicon nitride interfacial layer between the silicon substrate and the scandium oxide layer improves interface quality, as interfacial state density and defect density inside the insulator are decreased.
    Thin Solid Films 01/2011; 519(7):2268-2272. · 1.87 Impact Factor
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    ABSTRACT: SrTiO3-based MIM capacitors were electrically characterized. Strontium titanate thin films were grown by atomic layer deposition using Sr( i Pr3Cp)2 and (CpMe5)Ti(OMe)3 as strontium and titanium precursors and H2O and O3 as oxygen precursors. The temperatures used to grow the high-k films were 250 and 300 ºC. The films were amorphous in the as-deposited state. The lowest CET values were achieved in the films grown using ozone at 300 o C. Leakage current is lower when samples were grown at 250 ºC and when were grown using O3 as oxygen precursor.
    01/2011;
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    ABSTRACT: It is well known the gate dielectric conduction behaviour in high-k based MIS structures is usually dominated by more than one transport mechanism. In this work, results of the electrical performance of MIS structures on n- and p-Si using Al2O3, HfO2, and nanolaminated 10 nm-thick layers as gate insulators are reported. Clearly, different conduction mechanisms were observed depending on the applied bias: Fowler-Nordheim (FN) tunneling and Poole-Frenkel (PF) emission at high and moderate applied voltages, respectively, in accumulation regime and additionally, a negative-resistance region was only obtained in current-voltage (I-V) curves in inversion regime for Al2O3 based and nanolaminated films on p- Si instead of the usual saturated curves due to exhausting of the minority carriers. A model assuming the existence of a transition interlayer between the Al electrode and Al2O3 with a potential well capable of capturing electrons has been developed in order to explain this atypical effect. Despite the special focus of the study is on the mechanisms of conductivity, MIS structures were also electrically characterized using other techniques besides I-V, namely, capacitance-voltage (C-V), deep level transient spectroscopy (DLTS), conductance transients (G-t), and flat-band voltages transients (VFB-t) techniques. Al, Al2O3, HfO2, TMA, and TDMAH.
    01/2011;
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    ABSTRACT: The tunneling assisted charge exchange on the inner interface of high dielectric constant (high-k) dielectric stacks has been studied. The charging and discharching of traps existing at the HfO2/SiNx interlayer increase the transient capacitance amplitude, and so deep level transient spectroscopy (DLTS) measurements provide overestimated interfacial state density (Dit) values. This effect is quite important for very thin silicon nitride layers. The analysis of our experimental data allowed us to propose a physical model of the inner interface behavior.
    01/2011;
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    ABSTRACT: The influence of the silicon nitride blocking layer thickness on the interface state densities ( D <sub> it </sub>) of HfO <sub>2</sub>/ SiN <sub> x </sub>: H gate-stacks on n-type silicon have been analyzed. The blocking layer consisted of 3 to 7 nm thick silicon nitride films directly grown on the silicon substrates by electron-cyclotron-resonance assisted chemical-vapor-deposition. Afterwards, 12 nm thick hafnium oxide films were deposited by high-pressure reactive sputtering. Interface state densities were determined by deep-level transient spectroscopy (DLTS) and by the high and low frequency capacitance-voltage (HLCV) method. The HLCV measurements provide interface trap densities in the range of 10<sup>11</sup> cm <sup>-2</sup>  eV <sup>-1</sup> for all the samples. However, a significant increase in about two orders of magnitude was obtained by DLTS for the thinnest silicon nitride barrier layers. In this work we probe that this increase is an artifact due to the effect of traps located at the internal interface existing between the HfO <sub>2</sub> and SiN <sub> x </sub>: H films. Because charge trapping and discharging are tunneling assisted, these traps are more easily charged or discharged as lower the distance from this interface to the substrate, that is, as thinner the SiN <sub> x </sub>: H blocking layer. The trapping/detrapping mechanisms increase the amplitude of the capacitance transient and, in consequence, the DLTS signal that have contributions not only from the insulator/substrate interface states but also from the HfO <sub>2</sub>/ SiN <sub> x </sub>: H </- - formula> interlayer traps.
    Journal of Applied Physics 07/2010; · 2.21 Impact Factor
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    ABSTRACT: ZrO 2 and reference HfO 2 films grown by atomic layer deposition from metal cyclopentadienyls and ozone as precursors to thicknesses ranging from 3.6 to 13.1 nm on etched silicon showed electrical characteristics adequate to high-k dielectrics. The best results in terms of low interface state densities were obtained when CpMe 2 ZrMe 2 precursor was used, with Cp denoting the cyclopentadienyl group C 5 H 5 , and Me the methyl group CH 3 . The ZrO 2 films grown from CpMe 2 ZrOMeMe possessed nearly an order of magnitude higher trap state densities. Similar dependence on the precursor chemistry was observed upon recording the flatband voltage time transients. The flatband voltage transients, originating from phonon-assisted tunneling between localized states at oxide silicon interface, were the lowest in HfO 2 films grown from CpMe 2 HfOMeMe. The leakage current densities were also lower in the HfO 2 films, compared to ZrO 2 . On the other hand, interfacial trap state densities in HfO 2 based capacitors remained higher than those measured in the case of ZrO 2 films. Process-dependent qualities of the capacitors have been described. At the same time, the current conduction mechanisms in all films were essentially bulk driven, not affected noticeably by the interfacial barriers. © 2009 American Vacuum Society.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2009; 27(1). · 1.36 Impact Factor
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    ABSTRACT: The electrical characterization of ZrO2-based MIS structures fabricated by ALD on SiO2/Si substrates with monocyclopentadienyls of zirconium, ZrCp(NMe2)3, as precursors was carried out. These precursors combine the beneficial properties related to the high thermal stability of the Cp compounds with the high growth rate and tendency of forming high permittivity cubic or tetragonal ZrO2 phases of the alkylamido compounds. Interfacial state densities of annealed samples reached values as low as 1 times 1011 Cm-2 eV-1, and leakage current was essentially bulk driven, with similar values to those obtained when precursors contained two cyclopentadienyl groups. The hysteresis of C-V curves, as well as the amplitude of conductance and flat-band voltage transients had moderate values, indicating the good quality of the films.
    01/2009;
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    ABSTRACT: Ionizing radiation effects on the electrical properties of HfO2, Gd2O3, and HfO2/SiO2 based metal-oxide-semiconductor (MOS) capacitors have been studied. High-k dielectrics grown by atomic layer deposition and high-pressure Sputtering were exposed to photon radiation (18 MeV photons). Capacitance-voltage curves, deep-level transient spectroscopy, conductance and flat-band voltage transients, and current-voltage techniques were used to characterize the samples. An increment in bulk dielectric trap densities has been observed when the samples were exposed to the ionizing radiation. These traps give rise to a flat-band voltage displacement, the extent of which depends on the gate dielectric used. High-k/silicon interface quality becomes worse after irradiation. An increment in the gate leakage current was also observed when irradiating the samples. Disorder-induced gap state density inside the insulator increases in the case of Gd2O3 MOS based samples, which seems to be the most affected by ionizing radiation.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2009; 27(1):416. · 1.36 Impact Factor
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    ABSTRACT: Electrical characterization of zirconium oxide (ZrO2) based metal-oxide-semiconductor (MOS) structures has been carried out. ZrO2 films have been atomic layer deposited (ALD) by using novel cyclopentadienyl-based precursors, which have recently revealed themselves as very adequate in terms of thermal stability and high permittivity of the dielectrics deposited. Our results demonstrate good quality of the films, especially when mixed alkylamido-cyclopentadienyl precursors are used on SiO2/Si substrates. Conduction mechanisms in these MIS capacitors were studied, with moderately or highly-doped silicon used as substrate.
    Microelectronic Engineering 01/2009; 86:1689. · 1.22 Impact Factor
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    ABSTRACT: In this work, we show the existence of flat-band voltage transients in MIS capacitors with ultrathin high-k dielectric films. The transients are obtained when recording the gate voltage while keeping the capacitance constant at the value of flat-band condition (CFB). Gadolinium oxide and hafnium oxide are studied in this work. Transient time constant seems to be temperature independent, whereas the amplitude of the transient is thermally activated with energies in the range of soft-optical phonons usually reported for high-k dielectrics. So, the dependencies of transient time constant and amplitude on dielectric thickness and temperature, suggest that there are tunnelling assisted processes involved. Moreover, dependency of the flat-band voltage transient on the bias history, and on the sign of the capacitance-voltage curves is demonstrated.
    01/2009;
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    ABSTRACT: Zirconium oxide based metal-insulator-semiconductor (MIS) capacitors with highly doped Si substrates have been studied by electrical characterization. ZrO2 thin films were grown by atomic layer epostion (ALD), using ZrCp(NMe2)3 as precursor (with Cp=C5H5 and Me=CH3). The electrical measurements were carried out by using current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G-V) techniques. C-V and G-V curves indicated the behaviour of the interface states according to the frequency. Experimental evidence about tunnel conduction and bulk-controlled current, Poole-Frenkel effect, has been observed in different ranges of voltage.
    01/2009;
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    ABSTRACT: Al / HfO <sub>2</sub>/ SiN <sub>x</sub>: H /n -Si metal-insulator-semiconductor capacitors have been studied by electrical characterization. Films of silicon nitride were directly grown on n -type silicon substrates by electron cyclotron resonance assisted chemical vapor deposition. Silicon nitride thickness was varied from 3 to 6.6 nm. Afterwards, 12 nm thick hafnium oxide films were deposited by the high-pressure sputtering approach. Interface quality was determined by using current-voltage, capacitance-voltage, deep-level transient spectroscopy (DLTS), conductance transients, and flatband voltage transient techniques. Leakage currents followed the Poole–Frenkel emission model in all cases. According to the simultaneous measurement of the high and low frequency capacitance voltage curves, the interface trap density obtained for all the samples is in the 10<sup>11</sup> cm <sup>-2</sup>  eV <sup>-1</sup> range. However, a significant increase in this density of about two orders of magnitude was obtained by DLTS for the thinnest silicon nitride interfacial layers. In this work we probe that this increase is an artifact that must be attributed to traps existing at the HfO <sub>2</sub>/ SiN <sub>x</sub>: H intralayer interface. These traps are more easily charged or discharged as this interface comes near to the substrate, that is, as thinner the SiN <sub>x</sub>: H interface layer is. The trapping/detrapping mechanism increases the capacitance transient and, in consequence, the DLTS measurements have contributions not only from the insulator/substrate interface but also from the HfO <sub>2</sub>/ SiN <sub>x</sub>: H intralayer inter- face.
    Journal of Applied Physics 12/2008; · 2.21 Impact Factor