Search

© 1995 American Institute of Physics. This research has been partially supported by the Cooperation Programme “Azione Integrata” between Italy and Spain, We have investigated highly doped GaAs:Te at different doping concentrations (>10(17) cm(-3)) to assess the presence of the EL2 trap. We have utilized both capacitance and current transient spectroscopy techniques. The crucial parameter for the detection of EL2 is the relative position of the electron quasi-Fermi level in the depletion region. The observed shift of the EL2 apparent activation energy with increasing doping concentration is also discussed., Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

A tunnel-oxide-free GaN-based non-volatile memory (NVM) device is proposed to untangle the trilemma among speed, retention, and endurance in the implementation of conventional NVM. The program and erase (P/E) are based on bipolar charge injection controlled by individual junction barriers, whereas the data retention relies on bipolar charge trapping in an interfacial charge storage layer. The wide bandgap energy of GaN allows the formation of deep-level traps at a dielectric/GaN interface and high junction barriers in GaN, both of which benefit long-term retention. As such, the GaN-based NVM device could get rid of the tunnel oxide, thereby enabling faster P/E processes and facilitating to decouple the enhancement of endurance from that of speed and retention. The proposed device demonstrates a P/E time of 100 ns, endurance over 106 cycles, and long retention time. IEEE

Density functional theory (DFT) calculations of polyethylene (PE) HVDC cable insulation have been performed for systems containing four different chemical impurities: acetophenone, cumene, $\alpha$-methyl styrene and $\alpha$-cumyl alcohol. Systems were generated by molecular dynamics (MD) equilibration at four different temperatures relevant for cable insulation applications: 277 K, 293 K, 343 K and 363 K. With the goal of gaining better measure of variations in hole and electron traps energies, four initial configurations were also stochastically generated at each temperature, which yielded four different final configurations after equilibration. The counterpoise correction scheme was implemented for DFT calculations, by distributing ghost atoms thought any empty pockets of space in between the PE chains. The PBE functional was selected for DFT simulations. The resulting band gaps were in agreement with those of earlier GGA-based studies, and thus lower by 3 eV than empirical band gaps. For all impurities, the first HOMO state and the first two LUMO states were generally located on the impurity molecule, forming one hole trap and two electron traps, but certain configurations generated increased electron trap numbers, or eliminated hole traps. No dependence could be derived between temperature and trap depth for either electron or hole traps. Mean electron trap energies were largely in agreement with results from earlier studies, they were deepest for acetophenone, and they varied by as much as 0.6 eV between different configurations. Hole traps are universally shallow and vary by up to 0.7 eV between configurations, and are similar in depth for all impurities. Results suggest that electron trap depths correlate with the presence of molecular features such as oxygen atoms and conjugated double bonds. The dependence of trap depth on the spatial configuration of the impurity molecule suggests that results could be improved by more precise quantum mechanical treatmen, Täthetsfunktionalteori (DFT) har använts för beräkningar av isolering till HVDC kablar som består av polyeten innehållande fyra olika kemiska orenheter: acetofenon, kumen, alfa-metylstyren och alfa-kumylalkohol. System att studera genererades genom molekylärdynamisk ekvilibrering vid fyra olika temperaturer relevanta för tillämning till kabelisolering: 277 K, 293 K, 343 K och 363 K. För att få ett mått på de variationer som existerar i energierna på hål- och elektronfällor genererades stokastiskt fyra initialkonfigurationer vid varje temperatur, vilket fyra olika konfigurationer efter relaxering. Motviktskorrigering implementerades för DFT-beräkningar, genom att fördela "spökatomer" i de tomrum som bildas mellan PE-kedjorna i den amorfa fasen. PBE-funktionalen användes för DFT-simuleringar. De resulterande bandgapen stämde överens med tidigare GGA-baserade studier, och var därmed runt 3 eV smalare än empiriskt uppmätta bandgap. För alla orenheter var det första HOMO-tillståndet och de två första LUMO-tillstånden i allmänhet placerade på orenheten, vilket resulterade i en hålfälla och två elektronfällor, men vissa konfigurationer gav upphov till fler elektronfällor, eller eliminerade hålfällorna. Inget samband kunde härledas mellan temperaturen och djupet på fällorna för vare sig elektron- eller hålfällor. Medelvärdet på elektronfällornas energier överensstämde till stor del med resultat från tidigare studier, energierna var högst för acetofenon, och de varierade med så mycket som 0,6 eV mellan olika konfigurationer. Hålfällorna var genomgående grunda, varierade med upp till 0,7 eV mellan olika konfigurationer, och hade likartat djup för alla orenheter. Resultaten indikerar att variationerna elektronfällornas medeldjup uppstår på grund av orenheternas olika molekylära uppbyggnad: förekomst av syreatomer och konjugerade dubbelbindningar i orenheterna leder till djupare elektronfällor. Det faktum att djupet på elektron- och hålfällor varierar mellan olika rumsliga konf

Electron traps in polyethylene (PE) origin from water has been calculated using density functional theory. Atomistic structure has been simulated using molecular dynamics (MD) and used to calculate the electronic structure. Densities comparable with experimentally determined values are obtained. Both single water molecules and cluster of water molecules are considered. For a single water molecule both electron and hole states are within the bands from PE. The electron state is close to the conduction band minima (CBM) and may coincide with the CBM depending on the local atomic density. The absence of electron traps due to water is contradictory to previous simulation results but can be explained by atomic density and relaxation of conduction states of PE. Systems with 10 water molecules relaxed to two pentamers in the MD simulations. Calculation of trap levels of the pentamers result in trap levels in the order of 0.1-0.3 eV., QC 20230524

Density functional theory (DFT) calculations of polyethylene (PE) HVDC cable insulation have been performed for systems containing four different chemical impurities: acetophenone, cumene, $\alpha$-methyl styrene and $\alpha$-cumyl alcohol. Systems were generated by molecular dynamics (MD) equilibration at four different temperatures relevant for cable insulation applications: 277 K, 293 K, 343 K and 363 K. With the goal of gaining better measure of variations in hole and electron traps energies, four initial configurations were also stochastically generated at each temperature, which yielded four different final configurations after equilibration. The counterpoise correction scheme was implemented for DFT calculations, by distributing ghost atoms thought any empty pockets of space in between the PE chains. The PBE functional was selected for DFT simulations. The resulting band gaps were in agreement with those of earlier GGA-based studies, and thus lower by 3 eV than empirical band gaps. For all impurities, the first HOMO state and the first two LUMO states were generally located on the impurity molecule, forming one hole trap and two electron traps, but certain configurations generated increased electron trap numbers, or eliminated hole traps. No dependence could be derived between temperature and trap depth for either electron or hole traps. Mean electron trap energies were largely in agreement with results from earlier studies, they were deepest for acetophenone, and they varied by as much as 0.6 eV between different configurations. Hole traps are universally shallow and vary by up to 0.7 eV between configurations, and are similar in depth for all impurities. Results suggest that electron trap depths correlate with the presence of molecular features such as oxygen atoms and conjugated double bonds. The dependence of trap depth on the spatial configuration of the impurity molecule suggests that results could be improved by more precise quantum mechanical treatmen, Täthetsfunktionalteori (DFT) har använts för beräkningar av isolering till HVDC kablar som består av polyeten innehållande fyra olika kemiska orenheter: acetofenon, kumen, alfa-metylstyren och alfa-kumylalkohol. System att studera genererades genom molekylärdynamisk ekvilibrering vid fyra olika temperaturer relevanta för tillämning till kabelisolering: 277 K, 293 K, 343 K och 363 K. För att få ett mått på de variationer som existerar i energierna på hål- och elektronfällor genererades stokastiskt fyra initialkonfigurationer vid varje temperatur, vilket fyra olika konfigurationer efter relaxering. Motviktskorrigering implementerades för DFT-beräkningar, genom att fördela "spökatomer" i de tomrum som bildas mellan PE-kedjorna i den amorfa fasen. PBE-funktionalen användes för DFT-simuleringar. De resulterande bandgapen stämde överens med tidigare GGA-baserade studier, och var därmed runt 3 eV smalare än empiriskt uppmätta bandgap. För alla orenheter var det första HOMO-tillståndet och de två första LUMO-tillstånden i allmänhet placerade på orenheten, vilket resulterade i en hålfälla och två elektronfällor, men vissa konfigurationer gav upphov till fler elektronfällor, eller eliminerade hålfällorna. Inget samband kunde härledas mellan temperaturen och djupet på fällorna för vare sig elektron- eller hålfällor. Medelvärdet på elektronfällornas energier överensstämde till stor del med resultat från tidigare studier, energierna var högst för acetofenon, och de varierade med så mycket som 0,6 eV mellan olika konfigurationer. Hålfällorna var genomgående grunda, varierade med upp till 0,7 eV mellan olika konfigurationer, och hade likartat djup för alla orenheter. Resultaten indikerar att variationerna elektronfällornas medeldjup uppstår på grund av orenheternas olika molekylära uppbyggnad: förekomst av syreatomer och konjugerade dubbelbindningar i orenheterna leder till djupare elektronfällor. Det faktum att djupet på elektron- och hålfällor varierar mellan olika rumsliga konf

A tunnel-oxide-free GaN-based non-volatile memory (NVM) device is proposed to untangle the trilemma among speed, retention, and endurance in the implementation of conventional NVM. The program and erase (P/E) are based on bipolar charge injection controlled by individual junction barriers, whereas the data retention relies on bipolar charge trapping in an interfacial charge storage layer. The wide bandgap energy of GaN allows the formation of deep-level traps at a dielectric/GaN interface and high junction barriers in GaN, both of which benefit long-term retention. As such, the GaN-based NVM device could get rid of the tunnel oxide, thereby enabling faster P/E processes and facilitating to decouple the enhancement of endurance from that of speed and retention. The proposed device demonstrates a P/E time of 100 ns, endurance over 106 cycles, and long retention time.

This article aims to provide deep insight into the physics of substrates for RF applications under large-amplitude signal excitations. The impact of physical parameters on substrate-induced harmonic distortion is modeled and well understood, from a theoretical and quantitative standpoint. This article formulates the interplay between applied voltage signal (dc or RF), interface fixed charge, and trapped charge in a charge-balance analysis for high-resistivity and trap-rich (TR) substrates. A TCAD approach gives strong insight into the impact of such semiconductor material and interface properties on the RF substrate’s effective resistivity and linearity. First, a static analysis reveals how TR interface passivation overcomes the parasitic surface conduction effect using the concept of deep Fermi-level pinning. Next, substrates are analyzed in response to dynamic excitation signals. Using step functions to pulse an MOS structure from strong negative to strong positive applied charge sheds light on carrier dynamics. The characteristic time constants associated with variations in trap occupancy and in free carrier densities are discussed. Finally, sinusoidal large-amplitude signals are considered to analyze harmonic distortion from several types of substrates at various RF frequencies.

type:Journal Article, We report an observation of ultra-low-frequency self-oscillation of photocurrent in InxGa1–xAs/Al0.15Ga0.85As multiple-quantum-well p–i–n diodes. The photocurrent intensity shows self-oscillations with a characteristic frequency of ~0.1 Hz at low temperatures under reverse bias voltages. The photocurrent self-oscillation depends on applied bias voltage, temperature, illumination power, and indium content of quantum-well layers. These dependences indicate that the photocurrent self-oscillation is attributed to photogenerated carriers trapped in localized centers within InxGa1–xAs quantum-well regions., source:http://dx.doi.org/10.1063/1.1806268, source:http://www.aip.org

type:Journal Article, The thermal conductivity of n-type nanocrystalline bismuth-telluride-based thin films (Bi2.0Te2.7Se0.3) is investigated by a differential 3 method at room temperature. The nanocrystalline thin films are grown on a glass substrate by a flash evaporation method, followed by hydrogen annealing at 250 °C. The structure of the thin films is studied by means of atomic force microscopy, x-ray diffraction, and energy-dispersive x-ray spectroscopy. The thin films exhibit an average grain size of 60 nm and a cross-plane thermal conductivity of 0.8 W/m K. The in-plane electrical conductivity and in-plane Seebeck coefficient are also investigated. Assuming that the in-plane thermal conductivity of the thin films is identical to that of the cross-plane direction, the in-plane figure of merit of the thin films is estimated to be ZT=0.7. As compared with a sintered bulk sample with average grain size of 30 µm and nearly the same composition as the thin films, the nanocrystalline thin films show approximately a 50% reduction in the thermal conductivity, but the electrical conductivity also falls 40%. The reduced thermal and electrical conductivities are attributed to increased carrier trapping and scattering in the nanocrystalline film.

In this paper, static and dynamic performances of an AlGaN/GaN-on-Si power FET utilizing the integrated photonic-ohmic drain (PODFET) were systematically investigated. The operational mechanisms of the PODFET, including both the conditions of photon generation and the related physical processes, were explained. The dynamic switching tests were carried out under two types of hard switching conditions. With the photon generation and channel current inherently switched ON and OFF in synchronization, the dynamic performances of the PODFET can be significantly enhanced owing to photon pumping of deep electron traps. In addition, the generated photons were proved to be confined in proximity of the drain terminal without causing adverse effects on the device performances (e.g., the OFF-state leakage degradation). © 2016 IEEE.

In this work, static and dynamic characteristics of an AlGaN/GaN-on-Si power field-effect transistor (FET) with the integrated photonic-ohmic drain (POD) were systematically investigated. With the photon generation and channel current inherently switched ON and OFF in synchronization, dynamic performances (e.g. dynamic ON-resistance) of the PODFET can be significantly enhanced owing to photon pumping of deep electron traps. It is shown that the photons responsible for photon pumping of deep traps were confined in the proximity of the drain terminal without causing adverse effects on the device static performances (e.g. the OFF-state leakage degradation). Furthermore, the POD structure featured a robust tuning capacity on both breakdown voltage and threshold channel current for photon generation to the AlGaN/GaN power FET. © 2016 IEEE.

In this work, static and dynamic characteristics of an AlGaN/GaN-on-Si power field-effect transistor (FET) with the integrated photonic-ohmic drain (POD) were systematically investigated. With the photon generation and channel current inherently switched ON and OFF in synchronization, dynamic performances (e.g. dynamic ON-resistance) of the PODFET can be significantly enhanced owing to photon pumping of deep electron traps. It is shown that the photons responsible for photon pumping of deep traps were confined in the proximity of the drain terminal without causing adverse effects on the device static performances (e.g. the OFF-state leakage degradation). Furthermore, the POD structure featured a robust tuning capacity on both breakdown voltage and threshold channel current for photon generation to the AlGaN/GaN power FET. © 2016 IEEE.

In this paper, static and dynamic performances of an AlGaN/GaN-on-Si power FET utilizing the integrated photonic-ohmic drain (PODFET) were systematically investigated. The operational mechanisms of the PODFET, including both the conditions of photon generation and the related physical processes, were explained. The dynamic switching tests were carried out under two types of hard switching conditions. With the photon generation and channel current inherently switched ON and OFF in synchronization, the dynamic performances of the PODFET can be significantly enhanced owing to photon pumping of deep electron traps. In addition, the generated photons were proved to be confined in proximity of the drain terminal without causing adverse effects on the device performances (e.g., the OFF-state leakage degradation). © 2016 IEEE.

In this paper, static and dynamic performances of an AlGaN/GaN-on-Si power FET utilizing the integrated photonic-ohmic drain (PODFET) were systematically investigated. The operational mechanisms of the PODFET, including both the conditions of photon generation and the related physical processes, were explained. The dynamic switching tests were carried out under two types of hard switching conditions. With the photon generation and channel current inherently switched ON and OFF in synchronization, the dynamic performances of the PODFET can be significantly enhanced owing to photon pumping of deep electron traps. In addition, the generated photons were proved to be confined in proximity of the drain terminal without causing adverse effects on the device performances (e.g., the OFF-state leakage degradation). © 2016 IEEE.

In this work, static and dynamic characteristics of an AlGaN/GaN-on-Si power field-effect transistor (FET) with the integrated photonic-ohmic drain (POD) were systematically investigated. With the photon generation and channel current inherently switched ON and OFF in synchronization, dynamic performances (e.g. dynamic ON-resistance) of the PODFET can be significantly enhanced owing to photon pumping of deep electron traps. It is shown that the photons responsible for photon pumping of deep traps were confined in the proximity of the drain terminal without causing adverse effects on the device static performances (e.g. the OFF-state leakage degradation). Furthermore, the POD structure featured a robust tuning capacity on both breakdown voltage and threshold channel current for photon generation to the AlGaN/GaN power FET. © 2016 IEEE.

We present a quantitative analysis of the loss of electroluminescence in light-emitting diodes (LEDs) based on poly[2-methoxy-5-(2′-ethylhexyloxy)- p-phenylenevinylene] (MEH-PPV) due to the combination of non-radiative trap-assisted recombination and exciton quenching at the metallic cathode. It is demonstrated that for an MEH-PPV LED the biggest efficiency loss, up to 45%, arises from extrinsic non-radiative recombination via electron traps. The loss caused by exciton quenching at the cathode proves only to be significant for devices thinner than 100 nm. Removal of electron traps by purification is expected to enhance the efficiency of polymer LEDs by more than a factor of two. © 2012 Elsevier B.V. All rights reserved.

The performance of hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells is limited, as they contain a relatively high concentration of defects. The dark current voltage (JV) characteristics at low forward voltages of these devices are dominated by recombination processes. The recombination rate depends on the concentration of active recombination centers and the recombination efficacy of each of these centers. The first factor causes the ideality factor of the devices to be non-integer and to vary with voltage. The temperature dependence of the dark current can be expressed by its activation energy. For microcrystalline silicon solar cells the activation energy varies with voltage with a so-called thermal ideality factor of 2. This value was derived for devices with a spatially uniform defect distribution and reflects the recombination efficacy. Here we present results of a thickness series of a-Si:H p-i-n solar cells. We have matched the experimental curves with computer simulations, and show that the voltage-dependent ideality factor curve can be used to extract information on the cross sections for electron and hole capture. Also, the activation energy is used as a measure for the mobility gap, resulting in a mobility gap for a-Si:H of 1.69?eV. We find a thermal ideality factor close to 2 for all samples. This is explained with a theoretical derivation, followed by a comparison between the internal electric field strength and the spatial variation of the defect density in the intrinsic layer. The thermal ideality factor is shown to be insensitive to the defect distribution and the recombination profile in the device. It is, therefore, an appropriate parameter to characterize a-Si:H p-i-n devices, providing direct insight on the recombination efficacy., Electrical Sustainable Energy, Electrical Engineering, Mathematics and Computer Science

Major deep levels observed in as-grown and irradiated n-type 4H–SiC and 6H–SiC epilayers have been investigated. After low-energy electron irradiation, by which only carbon atoms are displaced, five traps, EH1 (Ec−0.36 eV), Z_1/Z_2 (Ec−0.65 eV), EH3 (Ec−0.79 eV), EH5 (Ec−1.0 eV), and EH6/7 (Ec−1.48 eV), were detected in 4H–SiC and four traps, E_1/E_2 (Ec−0.45 eV), RD_5 (Ec−0.57 eV), ES (Ec−0.80 eV), and R (Ec−1.25 eV), were detected in 6H–SiC. The Z_1/Z_2, EH6/7 centers in 4H–SiC and the E_1/E_2, R centers in 6H–SiC exhibit common features as follows: their generation rates by the e^−-irradiation were almost the same each other, their concentrations were not changed by heat treatments up to 1500℃, and they showed very similar annealing behaviors at elevated temperatures. Furthermore, these defect centers were almost eliminated by thermal oxidation. Taking account of the observed results and the energy positions, the authors suggest that the Z_1/Z_2 center in 4H–SiC corresponds to the E_1/E_2 center in 6H–SiC, and the EH6/7 center in 4H–SiC to the R center in 6H–SiC, respectively. Since the concentrations of these four centers are almost the same for as-grown, electron-irradiated, annealed, and oxidized samples, these centers will contain a common intrinsic defect, most likely carbon vacancy. The authors also observed similar correspondence for other thermally unstable traps in 4H–SiC and 6H–SiC.

The performance of hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells is limited, as they contain a relatively high concentration of defects. The dark current voltage (JV) characteristics at low forward voltages of these devices are dominated by recombination processes. The recombination rate depends on the concentration of active recombination centers and the recombination efficacy of each of these centers. The first factor causes the ideality factor of the devices to be non-integer and to vary with voltage. The temperature dependence of the dark current can be expressed by its activation energy. For microcrystalline silicon solar cells the activation energy varies with voltage with a so-called thermal ideality factor of 2. This value was derived for devices with a spatially uniform defect distribution and reflects the recombination efficacy. Here we present results of a thickness series of a-Si:H p-i-n solar cells. We have matched the experimental curves with computer simulations, and show that the voltage-dependent ideality factor curve can be used to extract information on the cross sections for electron and hole capture. Also, the activation energy is used as a measure for the mobility gap, resulting in a mobility gap for a-Si:H of 1.69?eV. We find a thermal ideality factor close to 2 for all samples. This is explained with a theoretical derivation, followed by a comparison between the internal electric field strength and the spatial variation of the defect density in the intrinsic layer. The thermal ideality factor is shown to be insensitive to the defect distribution and the recombination profile in the device. It is, therefore, an appropriate parameter to characterize a-Si:H p-i-n devices, providing direct insight on the recombination efficacy., Electrical Sustainable Energy, Electrical Engineering, Mathematics and Computer Science

Major deep levels observed in as-grown and irradiated n-type 4H–SiC and 6H–SiC epilayers have been investigated. After low-energy electron irradiation, by which only carbon atoms are displaced, five traps, EH1 (Ec−0.36 eV), Z_1/Z_2 (Ec−0.65 eV), EH3 (Ec−0.79 eV), EH5 (Ec−1.0 eV), and EH6/7 (Ec−1.48 eV), were detected in 4H–SiC and four traps, E_1/E_2 (Ec−0.45 eV), RD_5 (Ec−0.57 eV), ES (Ec−0.80 eV), and R (Ec−1.25 eV), were detected in 6H–SiC. The Z_1/Z_2, EH6/7 centers in 4H–SiC and the E_1/E_2, R centers in 6H–SiC exhibit common features as follows: their generation rates by the e^−-irradiation were almost the same each other, their concentrations were not changed by heat treatments up to 1500℃, and they showed very similar annealing behaviors at elevated temperatures. Furthermore, these defect centers were almost eliminated by thermal oxidation. Taking account of the observed results and the energy positions, the authors suggest that the Z_1/Z_2 center in 4H–SiC corresponds to the E_1/E_2 center in 6H–SiC, and the EH6/7 center in 4H–SiC to the R center in 6H–SiC, respectively. Since the concentrations of these four centers are almost the same for as-grown, electron-irradiated, annealed, and oxidized samples, these centers will contain a common intrinsic defect, most likely carbon vacancy. The authors also observed similar correspondence for other thermally unstable traps in 4H–SiC and 6H–SiC.

We propose a new method to realize a two-dimensional magnetic lattice, having two different configurations of asymmetric magnetic lattice, which exhibits magnetic band gap structure, and a symmetric magnetic lattice. We also describe the tunneling mechanisms of magnetically trapped ultracold atoms, prepared in a degenerate quantum gas such as Bose-Einstein Condensate (BEC). A coherent quantum tunneling of ultracold atoms between the sites of the asymmetrical magnetic lattice can be realized which induces the adiabatically controlled dc Josephson current. At critical phase transitions, namely at certain values of site phase difference and population fraction, a plasma oscillation can be observed in which it forms a discharging Josephson state to be used as coherently coupled n quantum bits.

The combination of piezoelectric materials and single crystal diamond offers the opportunity for the development of multifunctional micromachined devices under extreme conditions. In this work, the authors report the structural, electrical, optical, and dielectric properties of Pb(Zr0.52, Ti0.48)O3 (PZT) thin films integrated on single crystal diamond (100) substrates. The corresponding field effect transistor based on the metal-piezoelectric-insulator-semiconductor (MPIS) structure was fabricated on a homoepitaxial p-type diamond layer grown on a type-Ib diamond substrate. Different intermediate layers were deposited on single diamond substrates prior to the PZT films growth in order to achieve the best polarization properties. It was observed that the utilization of an Al2O3 buffer layer followed by a SrTiO3 seed layer favored the formation of a single perovskite PZT phase. Transmission electron diffraction patterns revealed that the PZT films included an initial layer at the SrTiO3/PZT interface followed by a well crystallized layer. The PZT film grown on SrTiO3/Al2O3/diamond exhibited much better in-plane polarization than that of the PZT film on Al2O3/diamond. The photoresponse behavior revealed that carriers trapping effect was trivial in the PZT film. The channel electrical conductivity of the MPIS field effect transistor was successfully modulated by the gate bias.

We propose a new method to realize a two-dimensional magnetic lattice, having two different configurations of asymmetric magnetic lattice, which exhibits magnetic band gap structure, and a symmetric magnetic lattice. We also describe the tunneling mechanisms of magnetically trapped ultracold atoms, prepared in a degenerate quantum gas such as Bose-Einstein Condensate (BEC). A coherent quantum tunneling of ultracold atoms between the sites of the asymmetrical magnetic lattice can be realized which induces the adiabatically controlled dc Josephson current. At critical phase transitions, namely at certain values of site phase difference and population fraction, a plasma oscillation can be observed in which it forms a discharging Josephson state to be used as coherently coupled n quantum bits.

The combination of piezoelectric materials and single crystal diamond offers the opportunity for the development of multifunctional micromachined devices under extreme conditions. In this work, the authors report the structural, electrical, optical, and dielectric properties of Pb(Zr0.52, Ti0.48)O3 (PZT) thin films integrated on single crystal diamond (100) substrates. The corresponding field effect transistor based on the metal-piezoelectric-insulator-semiconductor (MPIS) structure was fabricated on a homoepitaxial p-type diamond layer grown on a type-Ib diamond substrate. Different intermediate layers were deposited on single diamond substrates prior to the PZT films growth in order to achieve the best polarization properties. It was observed that the utilization of an Al2O3 buffer layer followed by a SrTiO3 seed layer favored the formation of a single perovskite PZT phase. Transmission electron diffraction patterns revealed that the PZT films included an initial layer at the SrTiO3/PZT interface followed by a well crystallized layer. The PZT film grown on SrTiO3/Al2O3/diamond exhibited much better in-plane polarization than that of the PZT film on Al2O3/diamond. The photoresponse behavior revealed that carriers trapping effect was trivial in the PZT film. The channel electrical conductivity of the MPIS field effect transistor was successfully modulated by the gate bias.

We observe ultrafast release and capture of charge carriers in InGaAs/GaAs quantum dots in a room-temperature optical pump-terahertz probe experiment sensitive to the population dynamics of conducting states. In case of resonant excitation of the quantum dot ground state, the maximum conductivity is achieved at approximately 35 ps after photoexcitation, which is assigned to release of carriers from the quantum dots. When exciting carriers into the conduction band of the barriers, depletion of the conductivity via carrier capture into the quantum dots with a few picosecond pump fluence-dependent time constant was observed.

Electric-field-induced resistive switching in metal-oxide interfaces has attracted extensive recent interest. While many agree that lattice defects play a key role, details of the physical processes are far from clear. There is debate, for example, regarding whether the electromigration of pre-existing point defects or the field-created larger lattice defects dominates the switch. We investigate several Ag-Pr0.7Ca0.3MnO3 samples exhibiting either submicrosecond fast switching or slow quasistatic dc switching. It is found that the carrier trapping potentials are very different for the pre-existing point defects associated with doping (and/or electromigration) and for the defects responsible for the submicrosecond fast switching. Creation/removal of the defects with more severe lattice distortions and spatial spreading (trapping potential ≥0.35eV), therefore, should be the dominating mechanism during submicrosecond switching. On the other hand, the shallow defects (trapping potential ⪡0.2eV) associated with doping/annealing are most likely responsible for the resistance hysteresis (slow switch) during quasistatic voltage sweep.

Two-dimensional semiconductor quantum dots are studied in the filling-factor range 2

Photo- and thermoluminescence (TL) spectra of NaLaF4:Ln3+ (Ln = Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm) and NaLaF4:Ce3+, Ln3+ (Ln = Nd,Sm,Ho,Er,Tm) are presented and used together with the empirical Dorenbos model in order to establish the 4f energy level positions of all tri- and divalent lanthanide ions doped in NaLaF4. The information will be presented in the form of an energy level diagram. It is shown that in addition to this diagram only two assumptions, viz., the presence of two host related electron traps and the presence of Vk-centers, are necessary for explaining the lanthanide-specific TL glow curves of both Ln mono- and Ce–Ln codoped NaLaF4., Radiation, Radionuclides and Reactors, Applied Sciences

We have observed the distribution of electron trapping centers on distorted carbon nanotubes (CNTs) by a unique x-ray analysis technique that has both elemental and spatial selectivities. This technique involves the use of scanning probe microscopy (SPM) under synchrotron radiation excitation of the inner shell of carbon. The probe detects the Coulomb force that results from the relaxation of an electron bound to a defect site into the core hole state created by x-ray photon absorption. This results in a change in charge state of the defect. At the spatial resolution provided by the SPM technique, we observed the electron trapping centers distributed on the compressed and torsionally distorted CNTs. This direct association of mechanical distortion with defect sites indicates a potential risk of deterioration of electric properties during the fabrication and processing of CNT networks., Applied Sciences

Carrying out a first-principles calculation assuming linear relationship between the electron density at Be nucleus and the electron-capture (EC) decay rate, we explained why 7Be@C60 shows higher EC decay rate than 7Be crystal, which was originally found experimentally by Ohtsuki et al. [Phys. Rev. Lett. 93, 112501 (2004)]. From the results of the calculation, we found that there are inequivalent four stable (i.e., lower energy) Be sites inside C60 and that center of C60 (C_C60) is the most favorable site. For C_C60, the electron density at the Be nucleus is the highest. It is also much higher than that at the Be nucleus in a Be crystal. Also, we estimated the expected electron density at the Be nucleus at room temperature by taking statistical average of the electron densities at the four Be nucleus sites using the Boltzmann distribution. The results of the calculation show fairly good agreement with the experimental results. In this paper, we focus on the detail of calculation, which was not fully demonstrated in the paper by Ohtsuki., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering

Photo- and thermoluminescence (TL) spectra of NaLaF4:Ln3+ (Ln = Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm) and NaLaF4:Ce3+, Ln3+ (Ln = Nd,Sm,Ho,Er,Tm) are presented and used together with the empirical Dorenbos model in order to establish the 4f energy level positions of all tri- and divalent lanthanide ions doped in NaLaF4. The information will be presented in the form of an energy level diagram. It is shown that in addition to this diagram only two assumptions, viz., the presence of two host related electron traps and the presence of Vk-centers, are necessary for explaining the lanthanide-specific TL glow curves of both Ln mono- and Ce–Ln codoped NaLaF4., Radiation, Radionuclides and Reactors, Applied Sciences

We have observed the distribution of electron trapping centers on distorted carbon nanotubes (CNTs) by a unique x-ray analysis technique that has both elemental and spatial selectivities. This technique involves the use of scanning probe microscopy (SPM) under synchrotron radiation excitation of the inner shell of carbon. The probe detects the Coulomb force that results from the relaxation of an electron bound to a defect site into the core hole state created by x-ray photon absorption. This results in a change in charge state of the defect. At the spatial resolution provided by the SPM technique, we observed the electron trapping centers distributed on the compressed and torsionally distorted CNTs. This direct association of mechanical distortion with defect sites indicates a potential risk of deterioration of electric properties during the fabrication and processing of CNT networks., Applied Sciences

Two-dimensional semiconductor quantum dots are studied in the filling-factor range 2

Carrying out a first-principles calculation assuming linear relationship between the electron density at Be nucleus and the electron-capture (EC) decay rate, we explained why 7Be@C60 shows higher EC decay rate than 7Be crystal, which was originally found experimentally by Ohtsuki et al. [Phys. Rev. Lett. 93, 112501 (2004)]. From the results of the calculation, we found that there are inequivalent four stable (i.e., lower energy) Be sites inside C60 and that center of C60 (C_C60) is the most favorable site. For C_C60, the electron density at the Be nucleus is the highest. It is also much higher than that at the Be nucleus in a Be crystal. Also, we estimated the expected electron density at the Be nucleus at room temperature by taking statistical average of the electron densities at the four Be nucleus sites using the Boltzmann distribution. The results of the calculation show fairly good agreement with the experimental results. In this paper, we focus on the detail of calculation, which was not fully demonstrated in the paper by Ohtsuki., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering

A combined photoconductivity, absorption, and thermoluminescence study was performed to understand the absence of luminescence from Ce3+ in LaAlO3:Ce3+. It is demonstrated that the absence of luminescence is the result of Ce3+ ionization from the 5d excited states, which are all located in the conduction band. Ce3+ ionization is accompanied by the formation of several broad absorption and photoconductivity bands, which are assigned to electron traps. A time and temperature dependent optical investigation of these traps reveals the conditions under which electrons are transferred from Ce3+ to traps and vice versa, from traps back to Ce4+. The observed difference in energy needed to thermally or optically release electrons from traps is qualitatively explained in terms of the location of the ground and excited states of the electron traps with respect to the conduction band., Radiation, Radionuclides and Reactors, Applied Sciences

Photoinduced interfacial charge carrier generation, separation, trapping, and recombination in TiO2?In2S3?CuInS2 cells have been studied with time-resolved microwave conductivity (TRMC). Single layer, double layer, and complete triple layer configurations have been studied. Selective electronic excitation in one of the components is accomplished by using monochromatic pulsed laser excitation. In bare CuInS2 films and in TiO2?CuInS2 double layers, photoinduced charge carriers recombine on a subnanosecond time scale. This fast recombination slows down significantly when an In2S3 buffer layer is applied between TiO2 and CuInS2. In that case, the charge separation lifetime increases by more than one order of magnitude. A superlinear dependence of the TRMC signals on the incident laser intensity is observed for the triple layer configuration, which indicates saturation of electron traps in In2S3 or hole traps in CuInS2. Furthermore, TRMC signals from TiO2?In2S3?CuInS2 triple junctions and those from In2S3?CuInS2 double layers are identical, which shows that charge carrier separation exclusively takes place at the In2S3?CuInS2 interface., DelftChemTech, Applied Sciences

Photoinduced interfacial charge carrier generation, separation, trapping, and recombination in TiO2?In2S3?CuInS2 cells have been studied with time-resolved microwave conductivity (TRMC). Single layer, double layer, and complete triple layer configurations have been studied. Selective electronic excitation in one of the components is accomplished by using monochromatic pulsed laser excitation. In bare CuInS2 films and in TiO2?CuInS2 double layers, photoinduced charge carriers recombine on a subnanosecond time scale. This fast recombination slows down significantly when an In2S3 buffer layer is applied between TiO2 and CuInS2. In that case, the charge separation lifetime increases by more than one order of magnitude. A superlinear dependence of the TRMC signals on the incident laser intensity is observed for the triple layer configuration, which indicates saturation of electron traps in In2S3 or hole traps in CuInS2. Furthermore, TRMC signals from TiO2?In2S3?CuInS2 triple junctions and those from In2S3?CuInS2 double layers are identical, which shows that charge carrier separation exclusively takes place at the In2S3?CuInS2 interface., DelftChemTech, Applied Sciences

A combined photoconductivity, absorption, and thermoluminescence study was performed to understand the absence of luminescence from Ce3+ in LaAlO3:Ce3+. It is demonstrated that the absence of luminescence is the result of Ce3+ ionization from the 5d excited states, which are all located in the conduction band. Ce3+ ionization is accompanied by the formation of several broad absorption and photoconductivity bands, which are assigned to electron traps. A time and temperature dependent optical investigation of these traps reveals the conditions under which electrons are transferred from Ce3+ to traps and vice versa, from traps back to Ce4+. The observed difference in energy needed to thermally or optically release electrons from traps is qualitatively explained in terms of the location of the ground and excited states of the electron traps with respect to the conduction band., Radiation, Radionuclides and Reactors, Applied Sciences

The transient properties of single grain–thin film transistors (SG-TFTs) with high electron mobility have been studied. Overshoot current induced by trap states has been observed in most of the devices. A method of ac measurements has been used to investigate the trap processes. Both transient and ac measurements show that the response of some SG-TFTs with high field effect mobility is dominated by a single trap level. Bias stressing on SG-TFT can induce more trap states and thus change the ac response of the device., Microelectronics & Computer Engineering, Electrical Engineering, Mathematics and Computer Science

High quality single crystals of ZnO in the as-grown and N+ ion-implanted states have been investigated using a combination of three experimental techniques - namely, positron lifetime/slow positron implantation spectroscopy accompanied by theoretical calculations of the positron lifetime for selected defects, temperature-dependent Hall (TDH) measurements and deep level transient spectroscopy (DLTS). The positron lifetime in bulk ZnO is measured to be (151 + 2) ps and that for positrons trapped in defects (257 + 2) ps. On the basis of theoretical calculations the latter is attributed to Zn+O divacancies, existing in the sample in both neutral and single negative charge states, and not to the Zn vacancy proposed in previous experimental work. From TDH measurements the concentrations of negatively-charged and neutral Zn+O divacancies are estimated to lie between 4 × 1015 and 6.3 × 1016 cm-3. DLTS revealed the creation of the defect E1 and an increase in concentration of the defect E3 after N+ ion implantation. Furthermore, a p-conducting layer is formed at the surface after the implantation/annealing procedure that can be used to inject holes during a DLTS measurement. In this way, the acceptor traps A2 and A3 with thermal activation energies of about 150 and 280 meV, respectively, have been detected for the first time by DLTS.

The transient properties of single grain–thin film transistors (SG-TFTs) with high electron mobility have been studied. Overshoot current induced by trap states has been observed in most of the devices. A method of ac measurements has been used to investigate the trap processes. Both transient and ac measurements show that the response of some SG-TFTs with high field effect mobility is dominated by a single trap level. Bias stressing on SG-TFT can induce more trap states and thus change the ac response of the device., Microelectronics & Computer Engineering, Electrical Engineering, Mathematics and Computer Science

Hydrogen related defects in high purity n-type float zone silicon samples have been studied by means of Deep Level Transient Spectroscopy. They were introduced, as well as the characteristic vacancy-oxygen (VO) and divacancy (V-2) centers, by MeV proton implantation. Two hydrogen related defect levels were resolved at 0.32 eV and 0.45 eV below the conduction band edge (E-c). Careful annealing studies indicate strongly that a third hydrogen related level, overlapping with the singly negative charge state level of V-2, is also present in the implanted samples. The annealing behavior of the hydrogen related defects has been compared with literature data leading to a rather firm identification. The E-c-0.32 eV level originates from a VO center partly saturated with hydrogen (a VOH complex) while the E-c-0.45 eV level may be ascribed to a complex involving a monovacancy and a hydrogen atom ( a VH complex). The third hydrogen related defect is tentatively ascribed to a complex involving a hydrogen atom and a divacancy ( a V2H complex)., QC 20100525

The production of stable vacancy-related point defects in proton-implanted float-zone and epitaxial silicon has been studied in the low dose range ( less than or equal to 10(10)/cm(2)) as a function of dose-rate. The well-known inverse dose-rate effect has been observed in both types of materials with a decrease in the concentration of vacancy-related defects as the dose-rate increases. The effect is less pronounced in oxygen lean epitaxial silicon. Moreover, a continuous decrease of the vacancy-related defect concentration as a function of the flux was measured while a threshold was expected according to previous studies. Both or these results can be explained by a simple calculation, taking into account the influence of the oxygen concentration as well as the influence of the diffusion coefficient of point defects on the inverse dose-rate effect., QC 20100525

We find two types of moving dark soliton textures in elongated condensates: nonstationary kinks and proper dark solitons. The latter have a flat notch region and we obtain the diagram of their dynamical stability. At finite temperatures the dynamically stable solitons decay due to the thermodynamic instability. We develop a theory of their dissipative dynamics and explain experimental data. © 2002 The American Physical Society.