Effective Capture Cross Section Research Articles

Investigation of traps in halide vapor-phase epitaxy-grown β-Ga2O3 epilayers/n+-Ga2O3 using deep-level transient spectroscopy

Abstract A detailed investigation of deep traps in halide vapor-phase epitaxy (HVPE)-grown β-Ga2O3 epilayers has been done by performing deep-level transient spectroscopy (DLTS) from 200 K to 500 K on Pt/β-Ga2O3 and Ni/β-Ga2O3 Schottky diodes. Similar results were obtained with a fill pulse width of 100 ms irrespective of the different Schottky metal contacts and epilayers. Two electron traps at E2 (E C–E T = 0.65 eV) and E3 (E C–E T = 0.68–0.70 eV) with effective capture cross-sections of 4.10 × 10−14 cm2 and 5.75 × 10−15 cm2 above 300 K were observed. Below 300 K, a deep trap with a negative DLTS signal peak was also observed at E1 (E C–E T = 0.34–0.35 eV) with a very low capture cross-section of 3.28 × 10−17 cm2. For a short pulse width of 100 μs, only two electron traps, E2 and E3, at energies of 0.72 eV and 0.73 eV were observed, and one order of higher corresponding effective capture cross-sections. All traps were found to be unaffected by the electric field during the field-dependent DLTS study. From the filling pulse width dependence DLTS study, a decrease in the capacitance transient amplitude with the increasing pulse width was observed opposite to the capture barrier kinetics of the traps and attributed to the emission of carriers during the capture process. Trap concentrations were found to be high at the interface using depth profiling DLTS. Based on the available literature, it is suggested that these traps are related to FeGa, Fe-related centers, and complexes with hydrogen or shallow donors, and might be affected or generated during metallization by the electron beam evaporator and chemical mechanical polishing.

Gravitational capture of magnetic monopoles by primordial black holes in the early universe

It is intriguing to ask whether the existence of primordial black holes (PBHs) in the early universe could significantly reduce the abundance of certain stable massive particles (SMP) via gravitational capture, after which the PBHs evaporate before BBN to avoid conflict with stringent bounds. For example, this mechanism is relevant to an alternative solution of the monopole problem proposed by Stojkovic and Freese, in which magnetic monopoles produced in the early universe are captured by PBHs, thus freeing inflation from having to occur during or after the corresponding phase transitions that produced the monopoles. In this work, we reanalyze the solution by modelling the capture process in the same way as the coexisting monopole annihilation. A subtle issue which is not handled properly in the previous literature is the choice of an effective capture cross section for diffusive capture. We model this aspect properly and justify our treatment. A monochromatic PBH mass function and a radiation-dominated era before PBH evaporation are assumed. We find that for Pati-Salam monopoles corresponding to a symmetry breaking scale between 1010 GeV and 1015 GeV, the capture rate is many orders of magnitude below what is needed to cause a significant reduction of the monopole density. Within our assumptions, we also find that the magnetic charge that is large enough to make an extremal magnetic black hole cosmologically stable cannot be obtained from magnetic charge fluctuation via monopole capture. The large magnetic charged required by cosmological stability can nevertheless be obtained from magnetic charge fluctuation at PBH formation, and if later the monopole abundance can be reduced significantly by some non-inflationary mechanism, long-lived near-extremal magnetic black holes of observational relevance might result.

Impact of effective capture cross-section on device performance of InAs/GaAs quantum dot solar cell

Impact of effective capture cross-section on device performance of InAs/GaAs quantum dot solar cell

Measurement of the Effective Capture Cross Section of 238Np in the High Flux Isotope Reactor

The cross sections of 237Np and 238Np are important for accurate modeling and simulation of 238Pu in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). Uncertainties in these cross sections can impact the ability to predict and optimize the target design and loading for 238Pu production targets. The effective capture cross section of 237Np in the location of pneumatic tube 1 in HFIR was measured as a first step in the measurement of the 238Np capture and fission cross sections. This paper describes the flux measurements, 237Np experiments, and data analysis of the 237Np capture cross section in HFIR.

Measurements of effective actinides neutron capture cross sections in a cadmium-filtered epithermal neutron spectrum

I (G.J.Y.) was a graduate student the first time I met Dr. Salvatores in February 1994 in Cadarache, France. He was teaching a class (in French) on fast reactor physics. Among us was a bright Chinese student who had come to learn reactor physics the French way. The student’s French was a little less than perfect, so I was surprised when, at the end of the class, he raised his hand and asked Dr. Salvatores, “Are you really French?” Dr. Salvatores looked at him and replied with a smile, “Eh, non, je ne suis qu’un pauvre paysan italien!” (No, I’m only a poor Italian peasant!) The class had a good laugh. It did not take long for me to realize Dr. Salvatores was more than just a “pauvre paysan italien”. Massimo would later become my Ph.D. director, and we had many occasions to meet and share laughs around the world over the next 25 years. He was an outstanding scientist, mentor, and bon vivant. He was a model and an inspiration for several generations of French nuclear reactor physicists involved in the development of fast reactors and advanced fuel cycles. Dr. Salvatores initiated the integral experiment that is the subject of this article.

The effect of crystal polymorphism of ferroelectric copolymer vinylidene fluoride‐hexafluoropropylene on its high‐voltage polarization

AbstractDielectric response of vinylidene fluoride‐hexafluoropropylene copolymer, crystallized in different polymorph modifications, to a high‐voltage electric field was studied. Polarization switching at high electric fields below coercive was detected. It was found that crystallization of the copolymer predominantly in nonpolar α‐phase is accompanied by more intensive growth of electric displacement at polarization. For the sample with higher content of polar γ‐phase, the value of high‐voltage conductivity “anomalously” decreased with increasing field at fields above coercive. The data on the field dependences of the remnant polarization showed that this should be attributed to an increase of the effective capture cross section of deep traps of γ‐phase polar planes for impurity and injected carriers. X‐ray diffraction has revealed the field‐induced transition of a part of the chains of the amorphous phase to the crystal.

Effects of control oxide material on the charging times of metal nanoparticles inside non-volatile memories: A 3-dimensional WKB calculation

We have investigated the influence of different control oxide materials on the charging times of metal nanoparticles (mNP) inside a [Si/SiO2/(mNP)/Control-Oxide/gate] non-volatile memory (NVM) in which the control oxide can have a higher dielectric constant ε than that of SiO2 like HfO2 or Al2O3 as is the case in practice frequently. Our calculations are performed for both N-type and P-type substrates. We have used a previously published 3-dimensional Wentzel–Krammers–Brillouin (WKB) method of ours, which does not contain such adjustable parameters as effective area or capture cross-section which other 1-dimensional theories use. To obtain the total time for the charging of the NVM to saturation we calculate the times that successive electrons take to be incorporated into an mNP under a given applied voltage and a given duration of the charging pulse, each time updating the tunneling potential due to the incorporation of the extra electron into the mNP. We obtain an exponential dependence of these charging times on the dielectric constant of the control oxide for which we offer a simple explanation. The change with substrate type is on the other hand less pronounced. Our results are confirmed by experiment. In particular, when our method is applied to NVMs with SiO2 and HfO2 as the control oxide we obtain good agreement with experiment without using such adjustable parameter as effective area of emission. We finally show that if the fraction of the substrate area that is covered with mNP is used to estimate this parameter the error involved will be quite significant, i.e. a factor of 5 approximately.

Single trap in liquid gated nanowire FETs: Capture time behavior as a function of current

The basic reason for enhanced electron capture time, τc, of the oxide single trap dependence on drain current in the linear operation regime of p+-p-p+ silicon field effect transistors (FETs) was established, using a quantum-mechanical approach. A strong increase of τc slope dependence on channel current is explained using quantization and tunneling concepts in terms of strong field dependence of the oxide layer single trap effective cross-section, which can be described by an amplification factor. Physical interpretation of this parameter deals with the amplification of the electron cross-section determined by both decreasing the critical field influence as a result of the minority carrier depletion and the potential barrier growth for electron capture. For the NW channel of n+-p-n+ FETs, the experimentally observed slope of τc equals (−1). On the contrary, for the case of p+-p-p+ Si FETs in the accumulation regime, the experimentally observed slope of τc equals (−2.8). It can be achieved when the amplification factor is about 12. Extraordinary high capture time slope values versus current are explained by the effective capture cross-section growth with decreasing electron concentration close to the nanowire-oxide interface.

MANTRA: An Integral Reactor Physics Experiment to Infer the Neutron Capture Cross Sections of Actinides and Fission Products in Fast and Epithermal Spectra

This paper presents an update of an on-going collaborative INL-ANL-ISU integral reactor physics experiment whose objective is to infer the effective neutron capture cross sections for most of the actinides of importance for reactor physics and fuel cycle studies in both fast and epithermal spectra. Some fission products are also being considered. The principle of the experiment is to irradiate very pure actinide samples in the Advanced Test Reactor at INL and, after a given time, determine the amount of the different transmutation products. The determination of the nuclide densities before and after neutron irradiation together with the neutron fluence will allow inference of effective neutron capture cross-sections in different neutron spectra.

Surface State Capture Cross-Section at the Interface between Silicon and Hafnium Oxide

The interfacial properties between silicon and hafnium oxide (HfO2) are explored by the gated-diode method and the subthreshold measurement. The density of interface-trapped charges, the current induced by surface defect centers, the surface recombination velocity, and the surface state capture cross-section are obtained in this work. Among the interfacial properties, the surface state capture cross-section is approximately constant even if the postdeposition annealing condition is changed. This effective capture cross-section of surface states is about 2.4 × 10−15 cm2, which may be an inherent nature in the HfO2/Si interface.

Electrical characterization of the AIIIBV-N heterostructures by capacitance methods

This paper highlights the electrical characterization of three types of the multiple quantum well (MQW) InGaAsN/GaAs heterostructures labelled NI58n, NI59n and NI66n with the nitrogen concentration of about 0.4% and indium content of 12.1%, 13.5% and 13.0%, respectively, using capacitance methods. These MQW InGaAsN/GaAs heterostructures were grown by atmospheric pressure metal organic vapour phase epitaxy (APMOVPE) at various growth conditions. The capacitance-voltage and DLTS measurements of these structures were performed utilizing the measurement system BIORAD DL8000.The CV characteristics measured at different temperatures on all heterostructures show very fine fluctuations of capacitance in the voltage range around 0V, which is suggested to be a result of free carriers’ emission from quantum wells. The absence of GaAs “cap” layer in one of the samples shifted its CV characteristic to lower values of capacity.According to the DLTS measurement it is highly probable that the similar system of defects is present in all samples. The presence of the deep level ET1 is clear in all samples and its parameters were calculated by multi level evaluation (the activation energy of the defect which is approx. ΔET=0.62eV, value of effective capture cross-section of the defect σT is about 10−16cm2, and defects concentration NT is about 1014cm−3).

Thermal ionization of an electron trap in Zn0.97Cd0.03S〈Cu,Cl〉 luminophore facilitated by electromodulation of the effective capture cross section

A fundamentally new mechanism of electric-field-stimulated luminescence (the Gudden-Pohl effect) has been established in a metal-dielectric-luminophore-metal (MDLM) structure with Zn0.97Cd0.03S〈Cu,Cl〉 powder luminophore. The luminescence observed during sequential excitation of the MDLM structure by light and electric field appears to be related to thermal ionization facilitated by electro-modulation of the effective electron capture cross section of a trap with an energy level of E c-0.18 eV.

Transient spectroscopy of Ryvkin’s α centers

The features of the DLTS detection of defects with retrappability of thermally excited carriers due to a large value of effective capture cross section are considered. Indications allowing identification of the implementation of the given model are found.

Re-Analysis of Recent Neutron Diffusion and Transmission Measurements in Nuclear Graphite

We revisit the determination by Bowman et al. of unusual neutron transport characteristics for a newly fabricated form of graphite [Nucl. Sci. Eng., 159, 182 (2008); Nucl. Sci. Eng., 161, 68 (2009)]. From MCNP modeling and consideration of data from other experiments, we determine revised values for the neutron transport parameters of this graphite. Our reanalysis gives a coherent scattering cross section σcoh ˜ 4 b at 50 meV, a small-angle neutron scattering cross section σsans ˜ 11 to 13 b at 1 meV, and an effective capture cross section σa = 5.8 ± 0.5 mb. Scaled to a graphite reference density of 1.60 g/cm3, we find a diffusion coefficient D̄ = 0.94 ± 0.03 cm and a diffusion length L = 47.7 ± 3.7 cm. Apart from the somewhat larger values of σa and D̄, these are not untypical parameters for graphite. Based on our investigation, the recent experiments and analysis of Bowman et al. do not give evidence for different transport properties for this newly fabricated graphite.

Interfacial and Electrical Characterization in Metal–Oxide–Semiconductor Field-Effect Transistors with CeO2 Gate Dielectric

Metal–oxide–semiconductor capacitors (MOSCs) and MOS field-effect transistors (MOSFETs) incorporating cerium dioxide (CeO2) dielectrics were fabricated and investigated. In this work, the electrical and interfacial properties were characterized by capacitance–voltage (C–V) and current–voltage (I–V) measurements. The density of interface trap per unit area (Nit), the density of interface trap per unit area and energy (Dit), the energy distribution of interface trap density, and the effective capture cross section (σs) were studied in details. Experimental results showed that the Nit, Dit, and σs were about 3.4×1010 cm-2, 7.3×1010 cm-2 eV-1, and 9.0×10-15 cm2, respectively. In addition, a comparison of interfacial properties among several gate dielectrics was made.

The Electrical and Interfacial Properties of Metal-High-$\kappa$ Oxide-Semiconductor Field-Effect Transistors With $\hbox{LaAlO}_{3}$ Gate Dielectric

LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> is a promising candidate for gate dielectric of future VLSI devices. In this letter, n-channel metal-oxide-semiconductor field-effect transistors with LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> gate dielectric were fabricated, and the electron mobility degradation mechanisms were studied. The leakage current density is 7.6times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at -1 V. The dielectric constant is 17.5. The surface-recombination velocity, the minority-carrier lifetime, and the effective capture cross section of surface states were extracted from gated-diode measurement. The rate of threshold voltage change with temperature (DeltaV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> /DeltaT) from 11 K to 400 K is -1.51 mV/K, and the electron mobility limited by surface roughness is proportional to E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-0.66</sup> .

Interface Characterization of CeO2-Gated MOSFETs Using Gated Diode Method and Charge Pumping Technique

Metal-oxide-semiconductor field-effect transistors (MOSFETs) incorporating CeO2 dielectrics were fabricated and investigated. In this work, the interfacial and electrical properties of CeO2/Si were characterized by gated-diode method and charge pumping technique. The lowest density of interface traps per area and energy (Dit) of CeO2/Si interface in comparison with other high-k material is about 7.3×1010 cm-2-eV-1 due to the very low lattice mismatch at CeO2/Si interface. The density of interface trap per area (Nit) determined using gated diode method is 6×109 cm-2. The minority carrier lifetime (tFIJ), the effective capture cross section of surface state (αs) and surface recombination velocity (so) extracted using gated-diode method are 4.09×10-8 s, 7.14×10-14 cm2 and 4310 cm/s, respectively. Furthermore, a comparison with MOSFETs using the other high-k materials as gate dielectrics was also made.

Interfacial and Electrical Characterization of HfO2-Gated MOSCs and MOSFETs by C-V and Gated-Diode Method

Metal-oxide-semiconductor capacitors (MOSCs) and Metal-oxide-semiconductor field-effect transistors (MOSFETs) incorporating hafnium dioxide (HfO2) dielectrics were fabricated and investi-gated. The electrical and interfacial properties were characterized including C-V, IDS-VGS, the mean density of interface traps per unit area and energy (), energy of interface traps density distribution, interface traps density (Nit), density of near-interface oxide traps per unit area (NNIOT), effective capture cross-section area (σs), mi-nority carrier lifetime (τFIJ) and surface recombination velocity (so) were studied. Furthermore, a comparison with MOSFETs using conventional SiO2 as gate dielectrics was also made.

Energy- and Time-Dependent Dynamics of Trap Occupation in 4H-SiC MOSFETs

A methodology for characterizing the transient response of 4H-SiC MOSFETs has been developed. The method combines new physical models, simulation techniques, and experiment to provide insight into the details of MOSFET time-dependent dynamics. A new physical model for generation-recombination between interface traps and channel electrons was derived, facilitating the analysis of trap dynamics in the energy, space, and time domains. A set of algorithms was developed, which enabled these rates to be incorporated into the drift-diffusion model so that their effect on the switching of 4H-SiC MOSFETs could be numerically evaluated. The correlation of simulated and experimental dc and transient drain current allowed the extraction of the density and the effective capture cross sections of interface traps. It was found that states near the band edge would become occupied much more quickly and had a much larger effective capture cross section than those that were several tenths of an electronvolt away from the band edge. This has led to the conclusion that the fast traps with large capture cross sections are likely to be interface states, whereas the traps with the smaller capture cross sections are a combination of midgap interface states and oxide traps. The observation of trap dynamics suggests that improvements in long-term device stability can be achieved by reducing oxide traps, whereas short-term stability can be improved by the reduction of interface traps.

Investigation of defects in Cu(In,Ga)(S,Se)2 films using the photocurrent decay technique

In the present work we demonstrate the possibility of using the photoinduced current transient spectroscopy (PICTS) method to study the defects in Cu(In,Ga)(S,Se)2 films which can be used as an absorber layer in solar cells (SCs). The conducted experiments enable one to determine the parameters (activation energies and effective capture cross-sections) of the defects revealed in the films under study.