Showing papers in "Physica E-low-dimensional Systems & Nanostructures in 2003"
TL;DR: In this article, the first energy transition 1h − 1e as a function of x and the well width was calculated for cubic AlxGa1−xN/GaN/AlxGa 1 −xN quantum wells and the nearest neighbor sp 3 s ∗ empirical tight binding approximation, together with the Surface Green Function Matching method was used.
Abstract: For cubic AlxGa1−xN/GaN/AlxGa1−xN quantum wells we calculated the first energy transition 1h–1e as a function of x and the well width. The nearest neighbour sp 3 s ∗ empirical tight binding approximation, including spin-orbit interaction, together with the Surface Green Function Matching method is used.
543 citations
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TL;DR: In this article, various techniques to combine metal and DNA, ranging from the application of a few atoms to complete metal coverage of the biomolecule, to the resulting properties of the assembled hybrid structures.
Abstract: The low intrinsic conductance of DNA seems to be a serious obstacle for the use of its unique self-assembly capabilities in nanoelectronics. The addition of metal atoms to the structure of DNA turned out to be a promising way to decrease the resistance significantly. Here, we review various techniques to combine metal and DNA, ranging from the application of a few atoms to complete metal coverage of the biomolecule. In addition, we investigate the resulting properties of the assembled hybrid structures. In some cases we obtain highly conductive nanowires, which exhibit the low temperature behaviour of polycrystalline metallic structures. Possible applications like single-electron devices or electronic DNA-recognition systems are discussed on the basis of their proof of concept studies.
161 citations
TL;DR: In this paper, the role of molecular beam epitaxy (MBE) in recent discoveries of the quantum Hall effect is discussed, and an overview of MBE's role in quantum Hall effects is given.
Abstract: We discuss the role of molecular beam epitaxy (MBE) in recent discoveries of the quantum Hall effect. An overview is given.
144 citations
TL;DR: In this article, a variable stripe length (VSL) method was used to measure the optical gain of silicon nanocrystals formed by thermal annealing at 1250°C of SiO x films.
Abstract: Observation of optical gain in silicon nanocrystals (Si-nc) is critically dependent on a very delicate balance among the Si-nc gain cross-sections, the optical mode losses and confinement factors of the waveguide structures, the Si-nc concentration and the strongly competing fast non-radiative Auger processes. Here we report on optical gain measurements by variable stripe length (VSL) method on a set of silicon nanocrystals formed by thermal annealing at 1250°C of SiO x films with different silicon contents prepared by plasma-enhanced chemical vapour deposition. Time-resolved VSL has revealed fast component in the recombination dynamics under gain conditions. Fast lifetime narrowing and superlinear emission has been unambiguously observed. To explain our experimental results we propose a four levels recombination model. Within a phenomenological rate equations description including Auger processes and amplified spontaneous emission we obtained a satisfactory agreement with time-resolved experiments and explained the strong competition between stimulated emission and fast non-radiative Auger processes.
120 citations
TL;DR: In this paper, the authors report on the fabrication and performances of extremely efficient Si-based light sources, which consist of MOS structures with erbium (Er) implanted in the thin gate oxide, and demonstrate strong 1.54 μm electroluminescence at 300 K with a 10% external quantum efficiency, comparable to that of standard light-emitting diodes using III-V semiconductors.
Abstract: We report on the fabrication and performances of extremely efficient Si-based light sources. The devices consist of MOS structures with erbium (Er) implanted in the thin gate oxide. The devices exhibit strong 1.54 μm electroluminescence (EL) at 300 K with a 10% external quantum efficiency, comparable to that of standard light-emitting diodes using III–V semiconductors. Er excitation is caused by hot electrons impact and oxide wearout limits the reliability of the devices. Much more stable light-emitting MOS devices have been fabricated using Er-doped silicon rich oxide (SRO) films as gate dielectric. These devices show a high stability, with an external quantum efficiency reduced to 1%. In these devices, Er pumping occurs by energy transfer from the Si nanostructures to the rare-earth ions. Finally, we have also fabricated MOS structures with Tb- and Yb-doped SiO2 which show room temperature EL at 540 nm (Tb) and 980 nm (Yb) with an external quantum efficiency of a 10% and 0.1%, respectively.
105 citations
TL;DR: In this paper, the authors considered the electrical interfacing of individual nerve cells and semiconductor microstructures as well as the assembly of neuronal networks and microelectronic circuits, where the planar core-coat conductor of a neuron-silicon junction is studied as it determines the coupling of ionconducting neurons and electron-conducting silicon and the width of the cleft between cell and chip, the resistance of cleft and voltage-gate ion channels in the junction are investigated.
Abstract: The electrical interfacing of individual nerve cells and semiconductor microstructures as well as the assembly of neuronal networks and microelectronic circuits, is considered At first the planar core–coat conductor of a neuron–silicon junction is studied as it determines the coupling of ion-conducting neurons and electron-conducting silicon The width of the cleft between cell and chip, the resistance of cleft and voltage-gate ion channels in the junction are investigated On that basis, a subsequent section describes the electronic interfacing of individual cultured neurons with silicon microstructures as well as the integration of microelectronics with small neuronal networks grown in culture In a final part, the electronic interfacing of cultured brain slices is addressed The goal of this approach is an integration of neuronal network dynamics and digital computation on a microscopic level for studies in brain research, biosensorics, information technology and medical prosthetics
97 citations
TL;DR: In this paper, it was shown that the bosonic model of superconductor-insulator transitions is only in qualitative agreement, as recent measurements suggest behavior more complex than a direct SI transition.
Abstract: Superconductor–insulator (SI) transitions in ultra-thin metal films, tuned either by magnetic field or disorder, have attracted substantial attention over the last decade, because of the possibility that they are quantum phase transitions. The bosonic picture of SI transitions proposed is at best only in qualitative agreement, as recent measurements suggest behavior more complex than a direct SI transition.
92 citations
TL;DR: In this paper, the authors discuss key issues related to quantum dot infrared photodetectors, including the normal incidence response, the dark current, and the responsivity and detectivity.
Abstract: We discuss key issues related to quantum dot infrared photodetectors. These are the normal incidence response, the dark current, and the responsivity and detectivity. It is argued that the present devices have not fully demonstrated the potential advantages. The dominant infrared response in devices so far is polarized in the growth direction. The observed dark currents are several orders of magnitude higher than those for quantum well photodetectors; while ideally they should be lower. The areas that need improvements are pointed out.
85 citations
TL;DR: In this paper, a new technique is used for achieving local gates in nanotube field effect transistors that provide excellent capacitive coupling between the gate and nanotubes, enabling the transistor to be ambipolar.
Abstract: We demonstrate logic circuits with field-effect transistors based on single carbon nanotubes. A new technique is used for achieving local gates in nanotube field-effect transistors that provide excellent capacitive coupling between the gate and nanotube, enabling the transistor to be ambipolar. The transistors show favorable device characteristics such as a high gain, a large on-off ratio, and room-temperature operation. Importantly, it also allows for the integration of multiple devices on a single chip. Indeed, we demonstrate 1-, 2-, and 3-transistor circuits that exhibit a wide range of digital logic operations such as an inverter, a logic NOR, and an AC ring oscillator.
81 citations
TL;DR: In this paper, the authors describe how to fabricate good quality 3 nm nc-Si with low size distribution in thermal SiO2 oxides, and show a good agreement between simulations and experimental data for the indirect gap of 3 nm dots which shows a threshold energy around 2 eV.
Abstract: In this work, we describe how to fabricate good quality 3 nm nc-Si with low size distribution in thermal SiO2 oxides. Photoluminescence, excited photoluminescence, and photocurrent measurements are discussed on the basis of theoretical calculations of the quantified levels in nc-Si. The impact of shape and size in quantum dots on transition energies has been highlighted, thanks to 2D symmetrical self-consistent Poisson–Schrodinger simulations. Both direct and indirect gaps in silicon have been considered in order to carry out a better comparison between simulations and optical measurements. A good agreement is found between simulations and experimental data for the indirect gap of 3 nm dots which show a threshold energy around 2 eV . However, the optical recombinations seems to be related to lower energy states probably due to interfacial radiative defects around 1.58 eV . On the basis of highly luminescent nc-Si, we have fabricated an optimized light emitting device (LED) with a calculated design in order to favour both electron and hole injection. Stable red electroluminescence has been obtained at room temperature and the I–V measurements confirm that the current is related to a pure tunnelling process. A modelling of I–V curves confirms a Hopping mechanism with an average trap distance between 1.4 and 1.9 nm . The Fowler–Nordheim process is not observed during light emission for electric fields below 5 MV / cm . Finally, we have not hot carrier injection and thus it seems possible to develop Si-based LEDs with a good reliability.
74 citations
TL;DR: In this article, a single quantum dot was used in a micropost microcavity to generate triggered single photons, which led to a large enhancement of spontaneous emission rate and allowed for strong coupling and single-dot lasing.
Abstract: We have used a single quantum dot in a micropost microcavity to generate triggered single photons. Coupling between the quantum-dot dipole and the confined microcavity mode leads to a large enhancement of the spontaneous emission rate. This, in turn, leads to efficient coupling of the emitted photons into a single traveling-wave mode. Optimization of the microcavity design should lead to nearly unity efficiency, and could also allow for strong coupling and for single-dot lasing.
TL;DR: In this article, the synthesis and properties of low-dimensional silicon structures in SiO 2 have been analyzed, and it is shown that an efficient carrier injection at low voltages and quite intense room temperature EL signals can be achieved, due to the sensitizing action of Si nc for the rare earth.
Abstract: In the last decade, a strong effort has been devoted towards the achievement of efficient light emission from silicon. Among the different approaches, rare-earth doping and quantum confinement in Si nanostructures have shown great potentialities. In the present work, the synthesis and properties of low-dimensional silicon structures in SiO 2 will be analyzed. All of these structures present a strong room temperature optical emission, tunable in the visible by changing the crystal size. Moreover, Si nanocrystals (nc) embedded in SiO 2 together with Er ions show a strong coupling with the rare earth. Indeed each Si nc absorbs energy which is then preferentially transferred to the nearby Er ions. The signature of this interaction is the strong increase of the excitation cross section for an Er ion in the presence of Si nc with respect to a pure oxide host. We will show the properties of Er-doped Si nc embedded within Si/SiO 2 Fabry–Perot microcavities. Very narrow, intense and highly directional luminescence peaks can be obtained. Moreover, the electroluminescence (EL) properties of Si nc and Er-doped Si nc in MOS devices are investigated. It is shown that an efficient carrier injection at low voltages and quite intense room temperature EL signals can be achieved, due to the sensitizing action of Si nc for the rare earth. These data will be presented and the impact on future applications discussed.
TL;DR: In this paper, the drain currents of nanometer double-gate MOSFETs with gate lengths in the range from 100 to 5 nm were calculated using a hierarchy of simulation approaches.
Abstract: The drain currents of nanometer double-gate MOSFETs with gate lengths in the range from 100 to 5 nm are calculated using a hierarchy of simulation approaches. By comparing Monte Carlo (MC), drift-diffusion (DD), and hydrodynamic (HD) simulation results the suitability of the DD and HD models for the investigation of the on- and subthreshold currents of nano-scaled MOSFETs is tested. Modifications of the velocity-field characteristics in the DD simulations are suggested to improve the accuracy of the DD model.
TL;DR: In this paper, the nonlinear electro-optic effects in quasi-one-dimensional semi-parabolic quantum wires are studied, in which the exciton effects are taken into account.
Abstract: The nonlinear electro-optic effects in quasi-one-dimensional semi-parabolic quantum wires are studied, in which the exciton effects are taken into account The analytical expression of the electro-optic co-efficient is derived by compact density-matrix approach Finally, the numerical results are presented for GaAs/AlGaAs semi-parabolic quantum wires The results show that the electro-optic coefficient is over two times bigger than that obtained by without considering exciton effects Furthermore, the electro-optic coefficient is related to the relaxation time
TL;DR: In this article, the dielectric layer consists of a substoichiometric SiO x (x thin film, annealed at 1100°C for 1 h to induce the separation of the Si and SiO 2 phases, with the formation of silicon nanocrystals (nc) embedded in the insulating matrix.
Abstract: We have fabricated MOS devices where the dielectric layer consists of a substoichiometric SiO x (x thin film , annealed at 1100°C for 1 h to induce the separation of the Si and SiO 2 phases, with the formation of silicon nanocrystals (nc) embedded in the insulating matrix. We have studied the electroluminescence (EL) properties of such devices as a function of the current density and of the temperature. We have evaluated the excitation cross section of Si nc under electrical pumping at room temperature and at low temperature (12 K ) . Moreover, we have used the experimental EL intensities and decay times to evaluate the radiative rate as a function of the temperature.
TL;DR: In this paper, electron tunneling through self-assembled monolayers of alkanethiols is investigated, and an exponential dependence of tunneling current on molecule length is observed.
Abstract: Electron tunneling through self-assembled monolayers of alkanethiols is investigated. Temperature-dependent current- voltage measurements are performed to distinguish between dierent conduction mechanisms. Temperature-independent electron transport is observed, proving direct tunneling as the dominant conduction mechanism of alkanethiols. An exponential dependence of tunneling current on molecule length is observed. Inelastic electron tunneling spectroscopy results are reported.
TL;DR: In this article, the performance characteristics of a MOSFET device with 15 nm physical gate length are discussed and aspects of a non-planar CMOS technology that bridges the gap between traditional CMOS and the nano-technology era are presented.
Abstract: Silicon transistors have undergone rapid miniaturization in the past several decades. Recently reported CMOS devices have dimensional scales approaching the “nano-transistor” regime. This paper discusses performance characteristics of a MOSFET device with 15 nm physical gate length. In addition, aspects of a non-planar CMOS technology that bridges the gap between traditional CMOS and the nano-technology era will be presented. It is likely that this non-planar device will form the basic device architecture for future generations of nano-technology.
TL;DR: In this paper, up to 75 layers of germanium, each about 8 monolayers thick, separated by Si-spacer layers (9-16 nm ) were grown on each other using standard 10 Ω cm p-type Si-substrates.
Abstract: We have fabricated silicon solar cells with embedded germanium layers to form three-dimensional islands in the Stranski–Krastanov growth mode. The additional Ge-layers increase the infrared absorption in the base of the cell to achieve higher overall photocurrent and overcome the loss in open circuit voltage of the heterostructure. In an UHV-MBE chamber up to 75 layers of germanium, each about 8 monolayers thick, separated by Si-spacer layers (9– 16 nm ) were grown on each other using standard 10 Ω cm p-type Si-substrates. The density of islands in the layers was increased by the use of antimony as surfactant, thus densities >10 11 cm −2 were realized. The islands were covered by a 200 nm thick Si-layer (n-type) on top which is used as emitter of the cell. Photoluminescence measurements, AFM and TEM-microscopy were used to characterize the growth of Ge-islands under various growth conditions and post-thermal treatment. Photocurrent measurements exhibit a higher response of the fabricated solar cells in the infrared regime compared to standard Si-cells.
TL;DR: In this article, the authors discuss the choice of the nanodevice parameters, which allows to get the confinement potentials with the designed shape: from the rectangular potential well to the potential well with smooth edges.
Abstract: In electrostatic (gated) quantum dots, the potential confining the electrons is generated by the electrostatic field, which is created by the external voltages applied to the leads. Changing the geometry of the nanodevice we can obtain a diverse class of confinement potentials. We discuss the choice of the nanodevice parameters, which allows us to get the confinement potentials with the designed shape: from the rectangular potential well to the potential well with smooth edges. In particular, we find the conditions, under which the confinement potential possesses the Gaussian shape or is parabolic in a large region of the quantum dot.
TL;DR: In this article, the impurity binding energy of V-shaped quantum wire (V-QWR) and rectangular wire was investigated with a variational procedure without using any coordinate transformation.
Abstract: We have studied theoretically the impurity binding energy for wires of different shapes (V-shaped quantum wire (V-QWR) and rectangular wire) with a variational procedure without using any coordinate transformation. The effective potential for V-QWR used in this work consists of a square well potential in the z-direction and full graded well potential in the x-direction. Our results are in good agreement with previous theoretical results, found by the coordinate transformation method. Furthermore, it is shown that the impurity binding energy in quantum wires is sensitive to the geometrical effects.
TL;DR: In this article, optical microscopy and spectroscopy on individual silver nanoparticles reveals strong emission for blue laser excitation for blinking and spectral fluctuations under continuous excitation, indicating that the emissive sites are small silver clusters photo-activated by light illumination of the oxide.
Abstract: Optical microscopy and spectroscopy on individual silver nanoparticles reveals strong emission for blue laser excitation. The silver nanoparticles ( 15 nm in size) are spin-coated on glass. The emitted light shows blinking and spectral fluctuations under continuous excitation. Identical spectral behaviour was observed on oxidised silver powder indicating that the emissive sites are small silver clusters (few atoms) photo-activated by light illumination of the oxide.
TL;DR: In this article, the authors show that the symmetry of the layers of the multi-wall tubes strongly affects the inter-wall interaction and that the total symmetry of tubes is highly reduced with respect to the high symmetry of isolated layers, and this results in low interaction which decreases with the symmetry breaking rate.
Abstract: We show that the symmetry of the layers of the multi-wall tubes strongly affects the inter-wall interaction. The total symmetry of the tubes is highly reduced with respect to the high symmetry of the isolated layers, and this results in low interaction which decreases with the symmetry breaking rate. The strongest interaction is found for the commensurate tubes with achiral walls. On the other side, the tubes with chiral walls interact negligibly. The results are used for detailed tribological study: various new phenomena are found and the tubes with maximal friction are selected.
TL;DR: In this paper, the authors reviewed the localization properties of electron states in the quantum Hall regime and provided a short review of the supersymmetric critical field theory, and the interplay between edge states and bulk localization properties was investigated.
Abstract: The localization properties of electron states in the quantum Hall regime are reviewed. The random Landau model, the random matrix model, the tight-binding Peierls model, and the network model of Chalker and Coddington are introduced. Descriptions in terms of equivalent tight-binding Hamiltonians, and the 2D Dirac model, are outlined. Evidences for the universal critical behavior of the localization length are summarized. A short review of the supersymmetric critical field theory is provided. The interplay between edge states and bulk localization properties is investigated. For a system with finite width and with short-range randomness, a sudden breakdown of the two-point conductance from ne 2 / h to 0 ( n integer) is predicted if the localization length exceeds the distance between the edges.
TL;DR: In this paper, the authors investigated the temperature dependence of the band gap energy in GaInNAs, GaNAs and InGaAs quantum wells and found that the S-shaped characteristic was observed at low temperatures.
Abstract: We have investigated the temperature dependence of the band gap energy in GaInNAs, GaNAs and InGaAs quantum wells. In the structures containing nitrogen the well-known S-shaped characteristic was observed at low temperatures. We explain this anomalous temperature behaviour by strong carrier localization in potential fluctuations at low temperatures. In the nitrogen free samples, there was no S-shaped behaviour and the empirical Varshni dependence was followed.
TL;DR: In this paper, a Si/SiGe HBT-type phototransistor with several Ge dot layers incorporated in the collector was developed to obtain improved light detectivity at 1.3-1.55 μm.
Abstract: The aim of this work is to develop a Si/SiGe HBT-type phototransistor with several Ge dot layers incorporated in the collector, in order to obtain improved light detectivity at 1.3–1.55 μm. The MBE ...
TL;DR: In this paper, the authors consider Kondo impurity systems with multiple local orbitals, such as rare earth ions in a metallic host or multi-level quantum dots coupled to metallic leads, and they use a slave boson mean field theory, which recovers the strong coupling Fermi liquid fixed point, to calculate the Kondo peak positions, widths, and heights analytically at T = 0.
Abstract: We consider Kondo impurity systems with multiple local orbitals, such as rare earth ions in a metallic host or multi-level quantum dots coupled to metallic leads. It is shown that the multiplet structure of the local orbitals leads to multiple Kondo peaks above the Fermi energy E F , each one with its own Kondo temperature T K , and to “shadow” peaks below E F . We use a slave boson mean field theory, which recovers the strong coupling Fermi liquid fixed point, to calculate the Kondo peak positions, widths, and heights analytically at T =0, and NCA calculations to fit the temperature dependence of high-resolution photoemission spectra of Ce compounds. In addition, an approximate conductance quantization for transport through multi-level quantum dots or single-atom transistors in the Kondo regime due to a generalized Friedel sum rule is demonstrated.
TL;DR: In this article, the authors studied the quantum dynamics of Cooper-pair-box qubits in a quantum electrodynamic cavity and showed the existence of Rabi oscillations for both single and multi-photon processes.
Abstract: We study the quantum dynamics of Cooper-pair-box qubits in a quantum electrodynamic cavity. We show the existence of Rabi oscillations for both single- and multi-photon processes and propose a quantum computing scheme.
TL;DR: In this article, the authors considered anisotropic pinning to transport magnetic flux quanta inside superconductor and showed that the applied electrical AC force is transformed into a net DC motion of fluxons, which can have important applications in devices like SQUID magnetometers, including convex and concave fluxon lenses.
Abstract: Motor proteins employ non-equilibrium fluctuations in anisotropic media to transport cargo at the cellular level. Here we consider anisotropic pinning to transport magnetic flux quanta inside superconductor. In particular, we consider: (1) composite pins by superimposing two interpenetrating arrays of weak and strong pinning centers; (2) triangular blind antidots; (3) V-shaped pinning sites. Specifically, we study stochastic transport of fluxons by alternating current (AC) rectification. Our simulated systems provide fluxon pumps, or fluxon “rectifiers”, because the applied electrical AC force is transformed into a net DC motion of fluxons. The asymmetry of the ratchet-shaped pinning landscape induce this “diode” effect, which can have important applications in devices, like SQUID magnetometers, and for fluxon optics, including convex and concave fluxon lenses.
TL;DR: In this article, a body-tied FinFET was proposed and fabricated on bulk Si wafer instead of SOI wafer, achieving an active fin width of 25-40 nm and a gate length of 40 nm.
Abstract: A new body-tied FinFET is proposed and fabricated on bulk Si wafer instead of SOI wafer. Three-dimensional device simulations show the characteristics of the proposed device and show that it can be implemented without deteriorating short channel effect. An active fin width of 25– 40 nm and a gate length of 40 nm were realized by using sidewall spacer technology.
TL;DR: In this article, the binding energy of excitons and interband optical absorption in quantum-well wires of GaAs surrounded by Ga1−xAlxAs is calculated in effective mass approximation, using a variational approach.
Abstract: The binding energy of excitons, and interband optical absorption in quantum-well wires of GaAs surrounded by Ga1−xAlxAs is calculated in effective-mass approximation, using a variational approach. Results obtained show that the exciton binding energies, and optical absorption depend on the sizes of the wire and strength of the electric field. The additional confinement of particles in quantum well wire offers greater variety of electric field dependence in comparison to bulk materials and quantum well structures.