[Show abstract][Hide abstract] ABSTRACT: The energy levels created in supersaturated n-type silicon substrates with titaniumimplantation in the attempt to create an intermediate band in their band-gap are studied in detail. Two titaniumion 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 cm−2 and 1014 cm−2, 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.
Preview · Article · Dec 2015 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Dysprosium-doped zirconium oxide thin films grown by atomic layer deposition (ALD) were studied in order to assess its suitability as dielectric in metal–insulator–metal (MIM) electronic devices. The films show high stability and linearity. The film quality clearly improves after annealing at 700 °C in O2 during 30 min. All films crystallize in as-deposited state and contained cubic and/or tetragonal ZrO2 phases. Current and charge measurements show hysteresis when varying the applied voltage. Structures with the highest Dy content in the dielectric showed the widest hysteresis cycles. Scanning electron microscopy reveals that the crystallite grain size increases with Dy content. A correlation between crystal grain size and I–V, and Q–V hysteresis exist, thus indicating that a charging process at the grain boundaries takes place.
No preview · Article · Nov 2015 · Microelectronic Engineering
[Show abstract][Hide abstract] ABSTRACT: Holmium titanium oxide (HoTiOx) thin films of variable chemical composition grown by atomic layer deposition are studied in order to assess their suitability as dielectric materials in metal-insulator-metal electronic devices. The correlation between thermal and electrical stabilities as well as the potential usefulness of HoTiOx as a resistive switching oxide are also explored. It is shown that the layer thickness and the relative holmium content play important roles in the switching behavior of the devices. Cycled current-voltage measurements showed that the resistive switching is bipolar with a resistance window of up to five orders of magnitude. In addition, it is demonstrated that the post-breakdown current-voltage characteristics in HoTiOx are well described by a power-law model in a wide voltage and current range which extends from the soft to the hard breakdown regimes.
No preview · Article · Sep 2015 · Thin Solid Films
[Show abstract][Hide abstract] ABSTRACT: The effects of 2 MeV electron irradiation on the electrical properties of high-k dielectric based metal–insulator–semiconductor capacitors have been studied. Samples consist of 5.9 nm-thick films of aluminum oxide and hafnium oxide deposited by atomic layer deposition on silicon substrates. Deep-level transient spectroscopy
(DLTS) and admittance measurements reveal that electron irradiation modifies the defect density of both surface states at the dielectric–semiconductor interface and border traps existing inside the dielectric. The experimental results indicate that irradiation has a double effect. The incident electrons transfer their energy and generate additional surface states, leading to a degradation of the interface. On the other hand, irradiation
generates electron–hole pairs inside the dielectric. Some of the holes are trapped by border traps located inside the dielectric at locations close to the interface. As a result, border traps capturing holes are neutralized and become inactive after irradiation. Moreover, interface state profiles, as measured by DLTS, are affected by the presence of border traps and yield overestimated interface state densities. Admittance spectroscopy is used to distinguish among border traps and interface traps. A detailed study of the conductance signal as a function of voltage, temperature and frequency for samples with different irradiation doses (nonirradiated, 2.5, 25, and 250 Mrad) is presented here. The influence of the irradiation dose has been analyzed in order to compare the defect distribution before and after irradiation.
[Show abstract][Hide abstract] ABSTRACT: MIS capacitors based on Dy2O3-doped ZrO2 oxide dielectrics were studied. The oxide films were grown by ALD. Defect concentrations at the oxide/semiconductor interface and inside the oxide depended on the film annealing that reduced the interface quality and increased defect densities inside the oxide. The leakage current density decreased at moderate voltages when the amount of dysprosium in the films increased.
[Show abstract][Hide abstract] ABSTRACT: In 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 = 176K 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.
No preview · Article · Jan 2015 · Applied Physics Letters
[Show abstract][Hide abstract] 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.
No preview · Article · May 2013 · Thin Solid Films
[Show abstract][Hide abstract] 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.
No preview · Article · Apr 2013 · Semiconductor Science and Technology
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: Due to the limitations in complementary metal-oxide-semiconductor (CMOS) scaling technology, the integration of novel materials to replace silicon dioxide (SiO2) as gate dielectric is required. Many high-k dielectrics have been extensively studied in order to fulfil the CMOS scaling down laws. Rare earth oxides, as ScO2 and Gd2O3, have been studied in order to replace silicon oxide. Even rare-earth scandate films (RE-ScO3) present a permittivity value higher than those of the constituent oxides, Gd2O3 and Sc2O3 .
The aim of this work is to study the electrical properties of metal-insulator-semiconductor (MIS) capacitors using scandium oxide (Sc2O3)as gate dielectric. High-k dielectrics were grown by high pressure sputtering (HPS). The HPS technique works at a pressure in the low mbar range, which lies between 2-3 orders of magnitude above conventional sputtering. In conventional systems the mean free path is much higher than the sample to target distance, thus the sputtered species reach the substrate by ballistic transport. In HPS the mean free path is typically in the order of few mm, so the sputtered species become thermalized in a distance of less than 1 cm due to many collisions with the plasma elements. Since the target to sample distance is typically 2 3 cm, the ion damage is greatly reduced and high quality films can be grown.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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]
No preview · Article · Jan 2013 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: The electrical properties of HfO2-based metal–insulator–semiconductor capacitors have been systematically investigated by means of I–V and C–V characteristics, admittance spectroscopy, deep level transient spectroscopy, conductance transient, and flat band voltage transient techniques. Attention is also given to the study of the temperature dependence of the leakage current. HfO2 films were grown on p-type silicon substrates by atomic layer deposition using hafnium tetrakis(dimethylamide) as hafnium precursor, and ozone or water as oxygen precursors. The growth temperature ranged from 150 to 350 °C. Low growth temperatures prevent decomposition and high growth rate, as well as high contamination levels. As a result, the leakage current is lower for lower deposition temperatures. Some of the deposited samples were submitted to a postdeposition annealing at 650 °C in N2 atmosphere, showing a decrease in the leakage current and an increase in the equivalent oxide thickness (EOT), whereas interfacial state density increases and defect density inside the dielectric bulk decreases. Regarding dielectric reliability, in our experimental conditions, HfO2 layers grown at 150 °C exhibit the largest EOT and breakdown voltage. The electrical behaviour is clearly linked with structural properties, and especially with the formation of an interfacial layer between the HfO2 layer and the silicon substrate, as well as with the presence of several impurities.
No preview · Article · Jan 2013 · Journal of Vacuum Science & Technology A Vacuum Surfaces and Films
[Show abstract][Hide abstract] ABSTRACT: In this work, the electrical characterization of Gd2O3 and Sc2O3-based metal-insulator-silicon (MIS) structures has been performed using capacitance-voltage, deep level transient spectroscopy, conductance transients, flat-band voltage transients, and current-voltage techniques. High-k films were deposited by high pressure sputtering using Sc and Gd metallic films in a pure Ar plasma and, subsequently, in situ room temperature plasma oxidation in a mixed Ar/O-2 atmosphere was performed. Three different metals were used as gate electrodes: aluminium, platinum, and titanium, in order to check electrical differences of the samples and to check the interface scavenging after high-k dielectric deposition. In particular, it was proved that Ti electrode is a well SiO2 interlayer scavenger for both materials. Additionally, the authors observed that the predominant conduction mechanism for these high-k based-MIS structures is Poole-Frenkel emission, as usually reported for high-k dielectrics. (C) 2013 American Vacuum Society. [http://dx.doi.org/10.1116/1.4768678]
Full-text · Article · Jan 2013 · Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society
[Show abstract][Hide abstract] ABSTRACT: Intermediate band silicon solar cells have been fabricated by Titanium ion implantation and laser annealing. A two-layer heterogeneous system, formed by the implanted layer and by the unimplanted substrate is obtained. In this work we present electrical characterization results which evidence the formation of the intermediate band on silicon when ion implantation dose is beyond the Mott limit. 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 non-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 increase is due to the big amount of charge trapped at the intermediate band, even at low temperatures. Titanium deep levels have been measured by Admittance Spectroscopy. These deep levels are located at energies which vary from 0.20 to 0.28 eV bellow 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 non recombinant. Admittance measurements are the first experimental demonstration the Intermediate Band is formation. 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.
[Show abstract][Hide abstract] 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.
No preview · Article · Feb 2011 · Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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 .
No preview · Article · Feb 2011 · Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society