Table of contents

This special issue of the Journal of Physics: Conference Series contains the proceedings of the joint Seventh International Conference on New Phenomena in Mesoscopic Structures and Fifth International Conference on Surfaces and Interfaces of Mesoscopic Devices, which was held from November 27th – December 2nd, 2005, at the Ritz Carlton Kapalua, Maui, Hawaii. The string of these conferences dates back to the first one in 1989. Of special importance is that this year's conference was dedicated to Professor Gottfried Landwehr, in recognition of his many outstanding contributions to semiconductor physics. A personal tribute to Prof Landwehr by Dr K von Klitzing leads off this issue.

The scope of NPMS-7/SIMD-5 spans nano-fabrication through complex phase coherent mesoscopic systems including nano-transistors and nano-scale characterization. Topics of interest include:

•Nanoscale fabrication: high-resolution electron lithography, FIB nano-patterning, scanning- force-microscopy (SFM) lithography, SFM-stimulated growth, novel patterning, nano-imprint lithography, special etching, and self-assembled monolayers •Nanocharacterization: SFM characterization, ballistic-electron emission microscopy (BEEM), optical studies of nanostructures, tunneling, properties of discrete impurities, phase coherence, noise, THz studies, and electro-luminescence in small structures •Nanodevices: ultra-scaled FETs, quantum single-electron transistors (SETS), resonant tunneling diodes, ferromagnetic and spin devices, superlattice arrays, IR detectors with quantum dots and wires, quantum point contacts, non-equilibrium transport, simulation, ballistic transport, molecular electronic devices, carbon nanotubes, spin selection devices, spin-coupled quantum dots, and nanomagnetics •Quantum-coherent transport: the quantum Hall effect, ballistic quantum systems, quantum-computing implementations and theory, and magnetic spin systems •Mesoscopic structures: quantum wires and dots, quantum chaos, non-equilibrium transport, instabilities, nano-electro-mechanical systems, mesoscopic Josephson effects, phase coherence and breaking, and the Kondo effect •Systems of nanodevices: Quantum cellular automata, systolic SET processors, quantum neural nets, adaptive effects in circuits, and molecular circuits •Nanomaterials: nanotubes, nanowires, organic and molecular materials, self-assembled nano wires, and organic devices •Nanobioelectronics: electronic properties of biological structures on the nanoscale.

This year's conference was organized by Prof Stephen Goodnick, Arizona State University, and Prof Yoshinobu Aoyagi, Tokyo Institute of Technology. The conference benefited from 14 invited speakers, whose topics spanned the above list, and a total of 97 registered attendees. The largest contingent was from Japan, followed closely by the US. In total, there were 49 from Japan, 31 fiom the US, and 17 from Europe. The organizers want to especially thank the sponsors for the meeting: The Office of Naval Research, the Army Research Office, and Arizona State University on the US side, and the Japan Society for the Promotion of Science, through their 151 Committee, on the Japanese side.

PROGRAM COMMITTEE •Prof Gerhard Abstreiter, Technical University of Munich •Prof Tsuneya Ando, Tokyo Institute of Technology •Prof John Barker, University of Glasgow •Prof Jonathan Bird, the University at Buffalo •Prof Robert Blick, University of Wisconsin •Prof David Ferry, Chair, Arizona State University •Dr Yoshiro Hirayama, NTT Basic Research Laboratories •Dr Koji Ishibashi, RIKEN •Prof Carlo Jacoboni, University of Modena •Prof David Janes, Purdue University •Prof Friedl Kuchar, University of Leoben •Prof K. Matsumoto, Osaka University •Prof Wolfgang Porod, Notre Dame University •Prof Michiharu Tabe, Shizuoka University •Prof Joachim Wolter, Eindhoven Institute of Technology •Prof Lukas Worschech, University of Würzburg •Dr Naoki Yokoyama, Fujitsu Research

The papers in this issue of the Journal of Physics: Conference Series represent the proceedings of the joint Seventh International Conference on New Phenomena in Mesoscopic Structures and the Fifth International Conference on Surfaces and Interfaces of Mesoscopic Devices. All manuscripts submitted for publication in the proceedings were subject to the usual peer-review process, which was undertaken during the period of the conference. This allowed for rapid publication of the proceedings, while ensuring that all submissions conformed to the quality standards of theJournal of Physics. It is my hope that this combination of rapid publication, and scientific rigor, will make this collection of manuscripts both a valuable and a timely resource.

Scientists all over the world know Gottfried Landwehr as Mister High Magnetic Field. In 1972, he started the conference series ``The Generation of High Magnetic Fields and their Application in Solid State Physics'' and acted as the director of the High Magnetic Field Laboratory in Grenoble at the time when the Quantum Hall Effect was discovered at this research center. His scientific interest in low temperature physics and semiconducting materials (mainly low dimensional electron systems) together with his strong connections to the Metrology Institute in Germany (Physikalisch Technische Bundesanstalt, PTB) formed the basis for scientific breakthroughs and discoveries with the Quantum Hall Effect as the main highlight. There is no doubt; he is the Grandfather of the Quantum Hall Effect.

I have known Gottfried Landwehr for more than 40 years, and first met him in Braunschweig at the PTB, where I worked as a summer student. Gottfried Landwehr had the privilege to run the ``Laboratory of the President'' which allowed him to do basic research within an excellent scientific environment. His main interests were magnetotransport phenomena in semiconductors such as germanium, tellurium and III/V semiconductors in pulsed magnetic fields up to 10 Tesla. His investigations on germanium bi-crystals opened the research field of low-dimensional electron systems, since the hole accumulation at the grain boundary between the crystals forms a two-dimensional hole gas. The accidental observation that (depending on the etching process) a two-dimensional hole gas can be formed not only at grain boundaries but also at the surface of an undoped tellurium crystal led to a concentration of Gottfried Landwehr's research into the field of two-dimensional electron systems. A fruitful cooperation with Gerhard Dorda at the Siemens Research Laboratory extended the research program in the direction of modern Silicon field effect transistors with pioneering transport research on n- and p-channels with different surface orientations. Even today, low-dimensional systems are one of the topics of his scientific research. Especially II/VI semiconductors with their applications as blue lasers or in spintronic are connected with the name Gottfried Landwehr. All these research activities have contributed to the topics of the international conferences ``New Phenomena in Mesoscopic Structures (NPMS)'' and ``Surfaces and Interfaces of Mesoscopic Devices (SIMD)''. In recognition of Gottfiied Landwehr's contribution to science and to the scientific community, the special joint mesoscopic conference NPMS/SIMD 2005 was dedicated to him.

C₆₀ nano-whiskers (C₆₀ NWs) have been synthesized by a method of liquid-liquid interfacial precipitation using a system of C₆₀-saturated m-xylene and isopropyl alcohol, and a C₆₀ nano-whisker based field-effect transistor (C₆₀ NW-FET) has been fabricated by a manipulator with use of a glass micro-capillary. The transport of the C₆₀ NW-FET exhibits n-channel normally on properties and their carrier mobility is estimated to be 2.5 × 10⁻² cm²/Vs in vacuum at room temperature.

We have investigated the photoluminescence (PL) of in individual single-walled carbon nanotubes (SWNTs) placed in field-effect transistor structures to study carrier transport in the SWNT. The relation between the recombination lifetime and carrier transit time has been evaluated from the drain-field dependence of PL intensity. Time-resolved photoluminescence of SWNTs dispersed in surfactant solution has also been studied to evaluate the recombination lifetime. From these results, the carrier saturation velocity was estimated.

We present experimental results on the electrical pulse-excited transport measurements of an individual single-wall carbon nanotube (SWNT) quantum dots. By applying a square pulse signal, the pulse-excited Coulomb peaks are observed in Coulomb oscillation measurements. In the SWNT quantum dot, the even-odd effect is confirmed by the alternate change of the Coulomb diamond size in the standard dc measurement. Magnetic fields perpendicular to the tube axis have revealed the simple Zeeman splitting of single particle states, this splitting is directly observed in the pulse-excited current in even-odd regime. We find the spin relaxation time at least longer than 1 µs.

A short-range part of the Coulomb interaction causes splitting and shift of excitons due to exchange interaction and mixing between different valleys in semiconducting carbon nanotubes. In the absence of a magnetic flux only a single exciton is optically active (bright) and all others are inactive (dark). Two bright excitons appear in the presence of an Aharonov- Bohm magnetic flux.

Quantum dots have been fabricated in single-wall carbon nanotubes (SWCNTs) simply by depositing metallic contacts on top of them. The fabricated quantum dots show different characteristics from sample to sample, which are even different in samples fabricated in the same chip. In this report, we study the statistical variations of the quantum dots fabricated with our method, and suggest their possible origin.

Conductance measurements of the transmembrane porin protein OmpF as a function of pH and bath concentration have been made with both a microfabricated silicon substrate device and a commercially available polystyrene aperture. Ion transport through the channel was simulated in atomic detail: the measured current was compared with theoretically calculated current, using a Brownian Dynamics kernel coupled to the Poisson equation by a P3M force field. The explicit protein structure and fixed charge distribution in the protein are calculated using the molecular dynamics code, GROMACS. Reasonable agreement is obtained in the simulated versus measured conductance over the range of experimental concentrations studied.

At the heart of a quantitatively accurate metal-molecule-metal conductance calculation, the potential profile must reflect the surface physics between the metal and vacuum. In this work, we employ a local orbital basis and calculate the conductance over a suite of Hamiltonians to examine trends within a molecular system using a rapid, selfconsistent scattering matrix method. As discussed above, this is justified as the tunneling barriers within the molecule largely determine the device's qualitative behavior. In this manner, the unexpectedly higher conductance experimentally measured on a four-membered oligothiophene, over its three-membered counterpart, is analyzed by calculating the conductance for a range of multi-atom displacements corresponding to a selected vibrational mode.

Based on the non-equilibrium Green's function formalism the performance of carbon nanotube field-effect transistors has been studied. The effects of elastic and inelastic scattering on the device performance have been investigated. The results indicate that elastic scattering has a more detrimental effect on the device characteristics than inelastic scattering. Only for short devices the performance is not affected because of the long mean free path for elastic scattering.

We report the characterization of electrical properties for multi-walled carbon nanotubes (MWNTs) synthesized by the arc-discharge method, as to the difference of characteristics between two diameters of 10 nm and 100 nm. In a result of Raman spectrums, we have observed clear radial-breathing-mode peak at approximately 255 cm⁻¹, which corresponds in turn to an innermost diameter of ∼2 nm in the MWNT, and shows a good agreement with the TEM image of diameter of the thin MWNT. The results of two- and fourterminal measurements of the thin MWNTs show a power-law behavior as expected for the Tomonaga-Luttinger liquid model. The power-law exponent, α ∼ 0.4, seems consistent with the one-dimensional nature of the transport in these structures. We have also investigated the thick MWNTs.

Third-order nonlinear susceptibility of single wall carbon nanotubes thin film was measured to be ∼1.4 × 10⁻¹⁶ m²/V². The nonlinear transmission limiting threshold of carbon SWNT was ∼20 MW/cm² with visible and nanosecond laser excitation.

We demonstrate DNA field effect transistor (DNA-FET) using multiwalled carbon nanotube (MWNT) as nano-structural source and drain electrodes. The MWNT electrodes have been fabricated by focused ion-beam bombardment (FIBB). A very short channel, approximately 50 nm, was easily formed between the severed MWNT. The current-voltage (I-V) characteristics of DNA molecules between the MWNT electrodes showed hopping transport property. We have also measured the gate-voltage dependence in the I-V characteristics and found that poly DNA molecules exhibits p-type conduction. The transport of DNA-FET can be explained by two hopping lengths which depend on the range of the source-drain bias voltages.

The inter-tube conductance is quite small in double-wall carbon nanotubes. When both edges are present in the outer tube or the inner tube, the conductance exhibits wild and discrete fluctuations as a function of the tube length and varies smoothly with a small oscillation as a function of the shift in the relative position of the outer and inner tubes. When one edge is in the outer tube and another in the inner tube like in telescoping tubes, the conductance exhibits a smooth but irregular oscillation as a function of the length corresponding to a certain combination of the length and position change.

The inductors made of carbon Nanotube (CNT) have been proposed. Though the fabrication of the proposed inductor is still challenging and has many problems, merits of the proposed inductor are following,

(i)The magnetic field induced by the current in CNT is about one thousand times larger than that induced by the current in normal copper wire.

(ii)The large magnetic field results in the large inductance, according to the relation between magnetic field and inductance.

(iii)The inductor made of CNT is smaller than the inductor in IC circuits, because CNT can be bent with small curvature.

Resonant third-order optical susceptibility and hyperpolarizability of donor polymer in chloroform were revealed to be ∼2.5 − 9.1 × 10⁻²⁰ m²/V² and ∼8.6 × 10⁻⁴² m⁵/V² by degenerate four-wave mixing in nanosecond scale at 532 nm, which was attributed to the resonant enhancement.

Magnetoresistance (MR) in single-walled carbon nanotubes (SWNTs) with different ferromagnetic source and drain electrodes (iron and cobalt) which have different coercivity was studied. Large MR ratio of 20% could be obtained at 8 K, while 1∼2% small MR ratio could be observed for the sample with the same ferromagnetic source and drain electrodes of Co. The MR ratio of 20% is very close to the theoretically predicted value of 26% for Co-Fe system.

Due to the small size, sensitivity, real time detection, and ultra-low power demands, nanowire sensors are being investigated for detection of a wide range of chemical and biochemical species. However, techniques used to fabricate these nanowire sensors have drawbacks of limited controllability and manufacturability. Reliable and controllable nanowire fabrication remains a significant challenge. In this work, we have developed a fabrication technique that is potentially capable of producing arrays of individually addressable nanowire sensors with controlled dimensions, positions, alignments, and chemical compositions and are in the process of fabricating sensor arrays to detect gases, and biochemicals. Fabrication of single Pd nanowires with diameters from 70 nm to 300 nm and up to 7 µm in length will be presented. These nanowires are used to sense hydrogen gas at concentrations as low as 0.02% and show a response time of 300 msec with an operating power of 350 nW. We also recently demonstrated the feasibility of fabricating single polypyrrole and polyaniline nanowires and their application as DNA sensor (1 nM). Currently, we are investigating single nanowire field effect transistors (SNWFET) for possible applications which include label-free DNA detection, early detection of disease signatures, and environmental monitoring.

Using the recursion-transfer-matrix (RTM) method combined with the nonequilibrium Green's function (NEGF) method, we study the electronic states and current-voltage (I-V) characteristics of atomic-scale nanocontact systems. We find that non-linear behaviors appear in the I-V characteristics even without molecules between electrodes. Such non-linear behaviors emerge when the nanocontacts are not well constructed and the transport properties change from tunneling to ballistic regimes.

Two dimensionally (2D) periodic pit structures are obtained by a lithograph technique on Si (001) substrate. Under proper growth conditions, the pit-pattern can be reserved after a thick Si buffer growth although the depth and the geometrical profiles of the pits are changed. During Ge deposition, GeSi islands preferentially grow at the pit bottoms, resulting in 2D ordered islands. In addition, the size homogeneity of these ordered islands is significantly improved. A kinetic model is proposed to qualitatively explain these results. By growing multilayer GeSi islands separated by thin Si spacers, three-dimensionally ordered islands or island crystal can be realized on pre-patterned substrates. These ordered islands helps to analyze the properties of a single island and island ensemble.

Coherent coupling and formation of molecular orbitals in vertically coupled quantum-dot molecules is studied for a seven-dot InAs/GaAs system. The electron states are computed using a nanoelectronic modelling tool NEMO-3D. The tool optimizes atomic positions in the sample with up to 64 million atoms in the frame of the atomistic VFF model. The resulting optimal interatomic distances are then used to formulate the 20-band sp3d5s^* tight-binding Hamiltonian defined on a subdomain large enough to guarantee a correct treatment of confined orbitals. It is found that in the absence of strain (VFF optimization turned off), a clear and highly symmetric miniband structure of the seven-dot orbitals is formed. It maintains a high degree of symmetry even if the dots are taken to be realistically non-identical, where the dot size increases in the growth direction. However, the inclusion of strain breaks this symmetry completely. The simulations demonstrate the important interplay of strain engineering and size engineering in the design of quantum dot stacks.

Two types of quantum point contacts have been studied by low temperature scanning gate microscopy. In addition to the usual bright spot, which corresponds to a large conductance change at the constriction, ring structures are observed near the center of the quantum point contact. The ring diameter shrinks with increasing base conductance when the side gate voltage is changed. The rings are thought to relate to the observation of impurity potentials in the constriction region.

We have investigated the non-linear transport properties of split-gate quantum wires of various channel lengths. In this report, we present results on a resonant enhancement of the non-linear conductance that is observed near pinch-off under a finite source-drain bias voltage. The resonant phenomenon exhibits a strong dependence on temperature and in-plane magnetic field. We discuss the possible relationship of this phenomenon to the spin-polarized manybody state that has recently been suggested to occur in quasi-one dimensional systems.

We present transport simulations of three-dimensional (3D) silicon quantum wires in which electron-phonon scattering is incorporated via local modifications to the potential encountered by the electron waves. Computing resistance as a function of wire length, we find that the effects of dissipation essentially take hold immediately, and are apparent right from the point at which the wire is long enough to act as a true waveguide.

Resonant third-order nonlinear optical susceptibility and hyperpolarizability of CdSe nanocrystal quantum dots were revealed to be ∼2.6×10⁻²⁰ – 2.7×10⁻¹⁹ m²/V² and ∼2.2×10⁻⁴⁰ m⁵/V² by using nanosecond degenerate four-wave mixing at 532 nm. The large nonlinearity of the CdSe nanocrystals is attributed to the resonant excitation and multiple nonlinear optical processes.

We report ab-initio calculations of the spin-dependent transport and magnetoresistance of Ni atom wires. The electronic states are calculated using a numerical pseudo atomic orbital basis set in the frame work of the density functional theory, and the conductance is calculated using the Green's function method. We show a magnetoresistance of 250%, which is explained by the scattering of d orbital channels.

A self-organized In_0.53Ga_0.47As/(In_0.53Ga_0.47As)₂(In_0.44Al_0.56As)₂ quantum wire (QWR) laser was grown on a (775)B InP substrate by molecular beam epitaxy (MBE). Well lattice-matched and flat cladding layers were grown at a rather high temperature (595° C). Lateral confinement potential was induced by a nano-meter scale interface corrugation of InGaAs/(InGaAs)₂(InAlAs)₂ with an amplitude of 2 nm and a period of 40 nm. A 50 µm × 500 µm stripe-contact QWR laser with uncoated cleaved mirrors oscillated with a threshold current density (J_th) of 1.2 kA/cm² and a lasing wavelength of 1370 nm at 250 K under pulsed current condition.

A new single electron (SE) binary-decision diagram (BDD) node device having a single quantum dot connected to three nanowire branches through tunnel barriers was fabricated using etched AlGaAs/GaAs nanowires and nanometer-sized Schottky wrap gates (WPGs), and their operation was characterized experimentally, for the hexagonal BDD quantum circuit. Fabricated devices showed clear and steep single electron pass switching by applying only an input voltage signal, which was completely different from switching properties in the previous SE BDD node devices composed of two single electron switches. As the possible switching mechanism, the correlation between the probabilities of tunnelling thorough a single quantum dot in exit branches was discussed.

We demonstrate a new type of velocity modulation transistor (VMT) with an InGaAs dual channel structure fabricated on an InP (001) substrate. The dual channel structure consists of a high mobility 10 nm In_0.53Ga_0.47As quantum well, a 2 nm In_0.52Al_0.48As barrier layer, and a low mobility 1 nm In_0.26Ga_0.74As quantum well. The VMTs have a negative differential resistance (NDR) effect with a low source-drain voltage of 0.38 V. The NDR characteristics can be clearly seen in the temperature range of 50 to 220 K with a gate voltage of 5 V. The NDR mechanism is thought to be the carrier transfer from the high mobility to the low mobility channels. Three-terminal VMTs are favorable for applications to highfrequency, high-speed, and low-power consumption devices.

Nonlinear transport properties of a ballistic rectifier fabricated from InAs/AlGaSb heterostructures are reported. The operation of the ballistic rectifier is based on the guidance of carriers by a square anti-dot structure. The structure was defined by electron beam lithography and wet chemical etching. The DC characteristics and magneto-transport properties of the ballistic rectifier have been measured at 77 K and 4.2 K. Rectification effects relying on the ballistic transport were observed. From the four-terminal resistance measured at low magnetic fields, we also observed magneto-resistance fluctuations corresponding to the electron trajectories and symmetry-breaking electron scattering, which are influenced by the magnetic field strength.

We fabricated side-gated quantum-dot structures on a GaAs/AlGaAs single heterostructure and measured their magnetoresistance at low temperature. We observed that oscillations appear almost periodic in B for a lower magnetic field region. We find that the oscillation period is fairly independent of the structure width. The experimental magnetoconductance are compared with numerical results.

Pt wires were fabricated by using electron-beam (EB) and Ga focused-ion-beam (FIB) irradiation while providing C₅H₅Pt(CH₃)₃ gas through a nozzle. Electron transport properties of the wires were investigated. The resistance of the EB-deposited wires was quite high as deposited but was reduced by 3-4 orders of magnitude after 400-500°C annealing. The electron transport of the as-deposited EB-deposited wire was dominated by the variable range hopping and the Coulomb blockade simultaneously, and showed the antilocalization effect after 400°C annealing. The electron phase-breaking length in the EB-deposited wire with 400°C annealing, which was derived from a theoretical fitting, is ≈10 nm at ≈4 K and increases with decreasing temperature. This means that 10-nm fabrication technology and improvement of coherence length are required for coherent vacuum nanoelectronics.

We investigate electron transport in silicon nanowires taking into account acoustic, non-polar optical phonons and surface/interface roughness scattering. We find that at very high transverse fields the reduced density of final states to which the carriers can scatter into gives rise to a reduced influence of interface-roughness scattering, which is promising result from a fabrication point of view.

We report the magneto-optical measurement of GaAs quantum wire lattices of 0.7 micrometer period grown on GaAs(111)B substrates by using the selective-area MOVPE technique. We measure the photoluminescence (PL) spectra at 60 mK from the triangular and the Kagome lattice patterns as well as from the unpatterned single quantum well (SQW) as a reference. While the PL from acceptors is dominant in all the samples, the PL spectra have a different peak between the wire structures and the SQW. When we apply a perpendicular magnetic field to the samples, the PL intensities slightly decrease up to 100 mT and then increase at higher magnetic fields with periodic oscillations in the triangular and the Kagome lattices. This oscillation is possibly attributed to the interference effect of electrons in the lattice patterns threaded by the magnetic flux.

We use a fully self-consistent three-dimensional quantum mechanical transport formalism to examine the performance of InAs based quantum wire transistors both in the ballistic limit and with phonon scattering included. We present a method for the inclusion of polar optical phonon scattering as a real-space self-energy term. We find that the ballistic performance of the devices can be recovered if the dopants in the system are kept away from the channel entrance and exit. When dopants are present at these key points, we find that the altered carrier energy, particularly in the source, has a significant impact on the device. This ballistic recovery is aided by the fact that at higher energies, polar optical phonon scattering loses its non-locality which leads to a reduced scattering rate in these confined systems.

We report on the generation of single-photon pulses from a single InAs/InP quantum dot in telecommunication bands (1.3-1.55 µm: higher transmittance through an optical fiber). First we prepared InAs quantum dots on InP (0 0 1) substrates in a low-pressure MOCVD by using a so-called InP 'double-cap' procedure. The quantum dots have well-controlled photo emission wavelength in the telecommunication bands. We also developed a single-photon emitter in which quantum dots were embedded. Numerical simulation designed the emitter to realize efficient injection of the emitted photons into a single-mode optical fiber. Using a Hanbury-Brown and Twiss technique has proved that the photons through the fiber were single photons.

The possible physical origin of third-order nonlinearity of cadmium chalcogenide (Te, Se, and S) semiconductor nanocrystals were discussed based on the results of both Z-scan and degenerate four-wave mixing spectroscopies at 532, 775, 800, and 1064 nm in nanosecond, picosecond, and femtosecond time scale for nonlinear photonic applications.

Bistable switching effect, induced by an electric field, in an anodic porous alumina thin film is reported. An electrode was bonded on the surface of a thin film with Ag paste, and I-V characteristic between the electrode and the aluminium substrate was measured The I-V characteristic reveals a reversible resistance change, initiating at + 4 V and terminating at −1.5 V at room temperature. Huge electrical resistance change ratio (RR), defined as the ratio of the resistance change to the low resistance state, is observed. The RR is approximately ten million. The resistance in the low resistance state was measured down to 18 K. The temperature dependence of the resistance shows a metal-like behaviour. The huge RR and the temperature dependence of the resistance suggest that an insulator-metal transition is occurred. Excellences of this device are huge RR ratio, easiness of mass production, and containing only common materials. It is a promising material for non-volatile memory with low power consumption and other electrical applications.

We have studied quantum effects on the piezoresistance (PR) of various kinds of low-dimensional heterostructures. The PR is strongly enhanced by electron interference in Q1D electron systems, by Landau qunatization in 2DEG systems, and also by the localizeddelocalized electronic state transition in quantum Hall systems. We have also studied PR for superconductor/semiconductor junctions and found that PR was enhanced at the critical current. In each system, the nonlinear response of device conductance against the change of magnetic field or bias current is responsible for the resistance change against the strain.

Several types of microfabricated mechanical filters are analyzed for RF communications applications and their advantages over the traditional SAW or FBAR filters are described. GHz frequency operation requires sub-micron dimensions. This work focuses on the modeling of a filter with torsional mode vibration. Ansys finite element simulation has been performed to make comparison with the analytical modelling. These devices enable a networked approach to control along with a specific application to velocity estimation in servocontrol.

We have analyzed the operation of the Bayesian quantum feedback of a solid-state qubit, designed to maintain perfect coherent oscillations in the qubit for arbitrarily long time. In particular, we have studied the feedback efficiency in presence of dephasing environment and detector nonideality. Also, we have investigated the effect of qubit parameter deviation.

A novel approach for measurement of single electron and nuclear spin states is suggested. Our approach is based on optically detected magnetic resonance in a nano-probe located at the apex of an AFM tip. The method provides single electron spin sensitivity with nano-scale spatial resolution.

We propose a novel approach to the development of a new generation of optical sensors with enhanced detection sensitivity for chemical species. The novelty comes from combining an extremely high Q cantilever sensor with an already well established very sensitive technique, frequency modulation (FM) spectroscopy. In existing implementations, this inherent sensitivity is limited by the inadequacy of current state-of-the-art electronic filters to differentiate the weak amplitude modulated (AM)signal from the inevitable high-frequency laser noise, a consequence of the deterioration in the quality factor with increasing frequency exhibited by these filters. Our approach combines FM techniques with the rapidly advancing technology of nano-mechanical resonator (cantilever) development. Here a cantilever functions as both a sensitive photodetector and a high-quality spectral or temporal filter. These ultra-low mass devices enable detection of the photon momentum rather than conventional detection by photon energy. At least one order of magnitude enhancement appears feasible with existing cantilever technology.

We present a new application of the quantum Hall effect (QHE): a scanning sensor for imaging the spatial distributions of noise voltages. This technique is based on a scanning electrometer employing a QHE device, which utilizes capacitive coupling between electrometer and sample. By measuring local voltage fluctuations with the QHE electrometer, we have been able to produce the first image of a noise-voltage distribution in a QHE sample. We found that a high noise level occurs in the lower magnetic field region of a QHE plateau of Landau-level-filling factor 2, and that it is concentrated in a high-potential edge region of the Hall bar sample. These results show that our noise-imaging system serves as a useful tool for probing edge-state electrons in QHE systems.

We theoretically study the bilayer ν = 1 quantum Hall system under an inplane magnetic field. When the in-plane field becomes strong, interlayer coherence in the system is suppressed by the field and the ground state is expected to show a phase transition from a commensurate state to an incommensurate one. We investigate a phase diagram of this system by analyzing the mode-softening properties of the random-phase-approximation excitation spectrum. The diagram indicates another phase between these ones and shows a qualitatively good agreement with the one obtained by a recent experiment.

Silicon MOSFETs with high κ gate stacks offer a significant reduction in gate leakage current, but the presence of soft surface optic phonon modes degrades the mobility. A progressively more complex set of models for SO phonon scattering at the Si-HfO₂ interface is presented based upon dynamic screening models. Landau damping of the electron-phonon-plasmon coupling is examined by simple approximations. A novel approach to determining the re-normalised phonon spectrum based on Padé approximants is outlined as a route to obtaining practical scattering rate for Monte Carlo simulation.

Variability in device characteristics will affect the scaling and integration of next generation nano-CMOS transistors. Intrinsic parameter fluctuations introduced by random discrete dopants, line edge roughness and oxide thickness fluctuations are among the most important sources of variability. In this paper the variability introduced by the above sources is studied in a set of well scaled MOSFETs with channel lengths of 25, 18, 13, and 9 nm. The effect of each source of intrinsic parameter fluctuation is quantified and compared. The random discrete dopants are responsible for the strongest variations followed closely by line edge roughness. The statistical independence of the different sources of fluctuations is also studied in the case of a 35 nm MOSFET.

A comparison of full quantum device simulation with semi-classical methods is made for an unintended single atomistic dopant at various locations in a 10 nm double gate MOSFET transistor. The density gradient method comes closest to the non-equilibrium Green function results for fails seriously when the unwanted charge is located well-within the channel.

Simulating nanoscale devices with high accuracy, particularly towards 10nm feature sizes, requires highly efficient fully quantum mechanical simulators. In this work fully quantum mechanical simulator based on Contact Block Reduction (CBR) method has been used to investigate the behaviour of 10nm FinFET device in the ballistic regime of operation. Simulation results show the transformation from multiple channels into a single merged channel as the fin width is reduced gradually. Also we observe that short channel effects can be minimized by reducing the fin width which is evident from the device transfer characteristics presented in this paper.

The performance potential of n-type implant free In_0.25Ga_0.75As MOSFETs with high-κ dielectric is investigated using ensemble Monte Carlo device simulations. The implant free MOSFET concept takes advantage of the high mobility in III-V materials to allow operation at very high speed and low power. A 100 nm gate length implant free In_0.25Ga_0.75As MOSFET with a layer structure derived from heterojunction transistors may deliver a drive current of 1800 A/m and transconductance up to 1342 mS/mm. This implant free transistor is then scaled in the both lateral and vertical dimensions to gate lengths of 70 and 50 nm. The scaled devices exhibit continuous improvement in the drive current up to 2600 A/m and 3259 A/m and transconductance of 2076 mS/mm and 3192 mS/mm, respectively. This demonstrates the excellent scaling potential of the implant free MOSFET concept.

Half-space Green functions and T-matrix theory is used to predict that scattering on discrete dopants close to a perfect interface generates strong deviations from scattering in the bulk. Interference between the scattered wave and its reflection from the interface leads to a dipolar scattering rate. By introducing de-coherence the transition to bulk scattering is described quantitatively for strongly screened Coulomb scattering.

Ultrafast operation of a transistor using ballistic electron concepts and its fabrication feasibility are shown by Monte Carlo simulation and experiment, respectively. The transistor consists of InP/GaInAs heterojunction launcher of 20 nm-width and a subsequent propagation layer of 80 nm-length intrinsic GaInAs. Schottky metal gates attached on both sides of the propagation layer are biased in the forward direction so that potential barriers at Schottky junctions are flattened and hot electrons are extracted from the launcher. Hot electron velocity is as fast as 7-8 × 10⁷ cm/s through the whole propagation layer. From stationary and step-response simulations, the cutoff frequency is higher than one THz. The emitter charging and the transit times are discussed to confirm the simulation. Finally, fabrication and operation of the transistor with 25 nm-width emitter using GaInAs/InP organo-metallic vapor phase epitaxy, electron-beam lithography, ultrafine process are demonstrated.

We have studied the impact of the channel composition fluctuations in pseudomorphic high electron mobility transistors (PHEMTs) on the device characteristics. The simulations are carried out using a 3D parallel finite element device simulator based on the drift-diffusion approximation to the semiconductor transport. The variation of the drain current introduced by the channel composition fluctuations increase with the increase of the gate and the drain voltage.

Atom intermixing processes at Au/Si(111), Al/Si(111), and Au/GaN(0001) interfaces are studied by using the first-principles calculations. It is shown that the motive force of intermixing is different between Au/Si and Al/Si interfaces; the production of Au-Si bonds causes the intermixing at Au/Si interface, while Al valence electrons screens Si-Si bonding and induces the intermixing at Al/Si interface. We show that the electronegativity and atomic radius are key quantities to control the intermixing at metal/semiconductor interfaces.

Linear light absorption of 2D electrons confined within a biased quantum well is studied theoretically. We demonstrate that for light polarization perpendicular to the 2D plane, in addition to conventional absorption peak at frequency ℏω ≈ Δ, where Δ is the intersubband energy distance, there exists a peak around a double frequency ℏω ≈ 2Δ. This additional peak is entirely due to electron-electron interactions, and corresponds to excitation of two electrons by one photon. The magnitude of two-electron absorption is proportional to U², where U is the applied bias.

We study theoretically excitonic energy spectrum and optical absorption in narrowgap semiconductor quantum wells in strong magnetic field. We show that, in the presence of an in-plane field component, the absorption coefficient exhibit a double-peak structure due to hybridization of bright and dark excitons. If both Rashba and Dresselhaus spin-orbit terms are present, the spectrum is anisotropic in in-plane field orientation with respect to [100] axis. In particular, the magnitude of the splitting can be tuned in a wide interval by varying the azimuthal angle of the in-plane field. The absorption spectrrum anisotropy would allow simultaneous measurement Dresselhaus and Rashba spin-orbit coefficients.

We study the plasma oscillations in a two-dimensional electron channel with a reverse-biased Schottky junction. Using the developed model we show that the negative dynamic conductivity of the Schottky junction associated with the tunneling injection and electrontransit- time effect can result in the self-excitation of plasma oscillations (plasma instability) in the quasineutral portion of the channel serving as a resonant cavity. The spectrum of plasma oscillations and the conditions of their self-excitations are expressed via the structure parameters. The instability can be used in a novel diode device - lateral Schottky junction tunneling transit-time terahertz oscillator.