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This paper is demonstrating the feasibility of using the native oxide film on GaAs surface grown by anodic oxidation in oxygen plasma as the gate insulator of GaAs insulated gate field effect transistor (IGFET). Especially the possibility of applying photolithography to the fabrication of IGFETs with this oxide was explored and it was assured by using dry etching process. IGFETs with the gate of 1µm length were fabricated. The high frequency performance is exemplified by the maximum stable power gain of 11.7dB at 8GHz and by the cut-off frequency of the unilateral power gain of 43GHz.

A new single flux quantum device is proposed, and, in conjunction with it, fabrication process of Josephson weak links using electron beam lithography and ion-etching is reported. Two types of niobium weak links, microbridges and thick-thin-thick type bridges, have been fabricated. They showed dc supercurrent, but microwave-induced steps were observed for thick-thin-thick type bridge only. The proposed logic device is constructed with a magnetically coupled rf-SQUID cells. These cells behave in the similar manner as “Domino-toppling”, and basic logic operations, AND, OR and NOT, are demonstrated by numerical calculations. Switching delay of about 10ps is expected to be practical.

Low temperature oxidation of silicon mesa transistors and alloy diodes is being undertaken by us for improving and stabilizing the characteristics. Oxidation at low temperature is more favorable to increase the freedom of design of silicon devices than at high temperature. For low temperature oxidation it seems necessary to make oxygen be chemically active to combine with silicon by some method, such as making it a dissociated state or ozone. Therefore, the devices are held in wet oxygen atmosphere between glass-covered electrodes which are connected to a source of high-voltage AC (saturable transformer). Following several hours oxidation in a quartz tube at atmospheric pressure and 300° C, results indicate that this method is most effective to increase the low current alpha of silicon mesa transistors up to that of silicon planar transistors and to decrease the saturation current of silicon p-n junctions.

Studies of electron phase coherence in open quantum dots reveal a subtle interplay between geometry and materials-related considerations. Suppressing environmental coupling, by reducing the width of the quantum point contact leads, a strong suppression of dephasing is observed. The magnitude of the phase-breaking time in this high-resistance regime shows large variations from device to device, indicative of a sensitivity to the specific disorder configuration in the dot. In order to account for our observations, we suggest an interpretation of phase breaking which invokes the discrete nature of the level spectrum in the open dots and which emphasizes the role of the quantum point contacts in selectively exciting cavity eigenstates.

We have studied the low-temperature magnetotransport in a semiconductor quantum dot and, using the correlation function method, observed evidence for the presence of a stabilized orbit in the case where only a few electron channels are present in the leads of the dot. Through quantum mechanical simulations of the device structure, we studied the nature of the orbits which underlie the presence of scarring of the wave function at periodically recurring magnetic fields. We also perform an analysis of possible geometry-induced fractal behavior on the magnetotransport in the quantum dot, which confirms the regularity of the dominant orbits.

We discuss the results of experimental studies of ballistic electron transport in regular (i.e. non-chaotic) quantum dots. At low temperatures, coherent interference between electrons gives rise to reproducible fluctuations in the magneto-resistance, as well as to a weak localization peak near zero field. The lineshape of the peak evolves from a Lorentzian to a linear form, as the leads of the dot are closed, while the fluctuations exhibit striking quasi-periodicity, suggesting that transport through regular dots is dominated by just a small group of trajectories. Simulations show that these characteristics in turn result from the ability of the quantum point contact leads, to strongly select which trajectories participate in transport.

We discuss the origin of a striking transition in the weak localisation lineshape observed in the low temperature magneto-resistance of ballistic quantum dots with square geometry. As the dot openings are gradually closed, the lineshape evolves from a Lorentzian to a linear form and, within the framework of the present theory, this behaviour can only be explained in terms of a corresponding transition from chaotic to regular behaviour within the devices. In order to determine the origin of this transition, we have performed classical simulations of ballistic transport within such dots, taking in to account the nature of the self-consistent potential. Poincare sections for the motion then indeed reveal a transition from chaotic to regular behaviour as the leads are pinched off, which appears to be associated with increasing collimation of the incoming electron beam.

We study the low-temperature magneto-resistance of split-gate corrugated wires, in which the application of a suitable gate voltage leads to the formation of an array of coupled dots. At magnetic fields where the cyclotron orbit is comparable to the size of the individual dots, a series of striking peaks is observed in the magneto-resistance. A simple geometric analysis suggests that the peaks arise from a commensurate focusing effect, involving only backscattered orbits within the array. This result is consistent with the behavior found in studies of individual quantum dots, in which the connection between conductance and backscattered orbits has recently been emphasized.

We measure the dependence of the phase breaking time on temperature and on dc voltage in ballistic split-gate quantum dots, the lead openings of which are defined by means of quantum point contacts. Estimates for the phase breaking time are obtained by studying the high-field evolution of the reproducible fluctuations, observed in the low-temperature magneto-conductance of the devices, and from the quenching of quantum interference induced by the dc bias. Varying either temperature or dc bias, a saturation of the phase breaking time is observed for sufficiently low values of these parameters. The energy scale at which the saturation onsets is found to be comparable to the average spacing of discrete levels within the quantum dot, indicative of a crossover to zero-dimensional phase breaking. Based on these observations, we suggest that studies of electron phase coherence may provide a powerful probe of the intrinsic eigenspectra of open quantum dots.

Experimental studies of the conductance of open quantum dots show a series of highly regular oscillations at low temperatures as the voltage applied to their defining gates is varied. Simulations of quantum transport through these dots reveal the oscillations to be correlated to the recurrence of specific groups of wave function scars. We furthermore find that nominally identical dots, differing only in the orientation of their input and output contacts, may be used to excite different families of scars, giving rise in turn to measurable transport results.

We have observed conductance fluctuations due to electron interference in a split-gate quantum dot, fabricated in the two-dimensional electron gas of a GaAs/AlxGa1 − xAs heterojunction. We have determined the phase breaking time of electrons by two independent analyses, using the correlation field and the amplitude of the fluctuations. Phase breaking times obtained by these distinct approaches are found to differ from each other by a factor of six.

We investigate electron interference in strongly confined GaAs/AlGaAs quantum dots, by studying the reproducible fluctuations in their low-temperature magneto-resistance. Spectral analysis of the fluctuations reveals a strong fundamental peak with well-defined harmonics, suggesting that transport can be dominated by the remnants of just a single classical orbit. The orbit is found to be relatively insensitive to changes in gate voltage or temperature, and its existence is also suggested by numerical simulations of the devices. Our results therefore demonstrate a survival of semi-classical ballistic transport that is very regular in mesoscopic devices, and so provide striking evidence that the remnants of certain classical orbits can be highly stable in the quantum environment.

We investigate the fractal magnetotransport properties of mesoscopic billiards. Employing three geometries, we find the self-similarity to be either statistical or exact. We use a correlation analysis to investigate the relationship between these two families of scaling behaviours.

We introduce a theory on phase breaking time, which predicts the temperature dependence of phase breaking time as 1/τϕ∝ kBT and geometrical effects characteristic of ballistic quantum dots. We also compare the result with the experimental data.

We have studied electron trajectories in a ballistic quantum dot with measurements of low temperature magneto-resistance and computer simulation of a quantum billiard. With only a few channels in the dot, we have observed a stable regular orbit which is a crossed one with small effective coherent area. The result shows evidence of a non-chaotic classical trajectory which also can be explained by wave function scarring.

We have found evidence of a transition from the semi-classical to quantum transport in quasi-ballistic narrow wires constructed in 2DEG system of a GaAs/AlGaAs heterojunction. By increasing the ratio of the mean free path to the wire length while keeping the wire width constant, we find a clear offset between the semi-classical and the quantum behaviors in the two-terminal measurement of the wire resisitance. We can explain such an offset by taking into account the transmission probability of electron waves propagating in the wire.

We study the effect of mode coupling on the magnetoconductance fluctuations of a square ballistic quantum dot fabricated in AlGaAs/GaAs heterostructure material and defined by Schottky gates. Structures prepared allow for the independent variation of the number of propagating input and output modes and their coupling to the main cavity. While adjusting the opening of the input and output point contacts changes the number of modes allowed to propagate into the dot, the excitation from a quantum wire creates an additional selection rule. The autocorrelation and Fourier analyses of the fluctuations demonstrate that the formation of the quantum wire has a strong effect, not only on the average conductance of the dot but also on the excitation of the semiclassical orbits within it.

We studied quantum interference effects observed in the low-temperature magnetoresistance of corrugation gated wires on a two-dimensional electron gas system. We have also studied the transport change due to deep gate depletion by means of the controlling gate voltage. We analyzed the gate voltage and magnetic field dependences of the negative magnetoresistance and observed small oscillations in the low-field magnetoresistances. The results show that a boundary-related or geometrical effect should strongly affect the phase-breaking mechanism in corrugation gated wires, and that the electron wave propagation differs between a narrow wire and a dot array, depending on the gate voltage.

Analysing the conductance fluctuations observed in low-temperature magnetoresistance, we study electron wave interference effects in the quasi-ballistic transport regime of a narrow wire, defined by split metal gates, on the two-dimensional electron gas of a GaAs/AlGaAs heterojunction. There is a clear difference in the conductance fluctuations between short and long wires of 2 and 6 μm gate length, respectively. Such a difference can be explained by considering whether some correlated channels exist in the wire or not.

We have studied electron wave interference effects in wires and dots in ballistic and quasi-ballistic transport regimes, fabricated by using split gate, or wet etching techniques. We observe conductance fluctuations as a function of magnetic field, and we show they arise from the different origin of the scattering source for interference. It is shown experimentally that scatterings occur at the boundaries of the wall in the ballistic sample, while they occur at impurities in quasi-ballistic sample. This difference is clearly demonstrated in the temperature dependence of the fluctuation amplitude and the shape dependent negative magnetoresistance peak due to the weak localization effect. We discuss also the phase breaking time in a ballistic dot, which is very important for the interference.

Magnetic characterization of a quantum dot array was carried out to extract the phase-breaking time as a function of temperature and current. These measurements indicate a saturation of the phase-breaking time at low temperature and low current. The phase-breaking time varies as 1 / T for temperatures above 1 K, which can be attributed to carrier–carrier scattering processes. Variation of the phase-breaking time with current yields an estimate for the electron temperature.

Future VLSI scaling realization of gate lengths is expected to 70 nm and below. While we do not know all the underlying physics, we are beginning to understand some limiting factors, which include quantum transport, in these structures. The discrete nature of impurities, the fact that devices have critical lengths comparable to their coherence lengths, and size quantization will all be important in these structures. These phenomena will lead to pockets of charge, which will appear as coupled quantum dots in the device transport. We review some of the physics of these dots.

We have studied the universal conductance fluctuations observed in the low-temperature magnetoresistance of quasiballistic, split-gate quantum-wire structures. Since transport in such devices is determined by scattering from only a small number of impurities, it is of interest to know whether the fluctuations exhibit the same universal features characteristic of corresponding metallic systems. In this paper, we discuss results obtained in split-gate wire structures of two different lengths (L=2 and 6 μm). These indicate that, although the fluctuations scale qualitatively as expected as the system size is varied, the amplitude of the scaling, expressed via the adjustable constant (J, is more than an order of magnitude smaller than the case for corresponding diffusive systems

Conductance Fluctuations due to the quantum interference of electrons have been studied in GaAs/AlGaAs narrow wires in the quasi-ballistic transport regime. Narrow channels of length 2 µm and 6 µm were confined by metallic split gates formed by electron beam lithography and a lift off technique. In the shorter wire, the amplitude of the fluctuations first increased as a function of increasing width, and finally approached to the constant value of e2/h. On the other hand, it was almost independent on channel width in the longer wire, as expected for the universal conductance mechanism in the diffusive transport regime. We suspect that the non universal width dependence in the shorter wire might result from averaging among the individual transmission channels, caused by the small number of scattering events.

Self-similarity ~the invariance of an intrinsic pattern under scaling ! in the fractal magnetotransport properties of mesoscopic billiards is highly topical. Employing three billiard geometries, we investigate the relationship between the two classes of observed scaling behavior—exact and statistical self-similarity. We employ a correlation analysis to determine the conditions required for their observation and to show that the two forms of self-similarity can be understood within a common framework. @S0163-1829~98!04934-0#

We have studied the low-temperature magnetotransport in the singly and doubly corrugated wires. The application of a sufficiently negative gate bias might result in the formation of weakly coupled dots. In the structures considered here the corrugations act as weak perturbations on the quantum wire. Compared with the experimental results and the numerical simulations of the transports in these perturbed quantum wires, we show that oscillatory magnetoresistance features, observed in the doubly corrugated wire, arise from back-scattered orbits. The observation of wave function scarring in the quantum simulations is given the open nature of the weakly perturbed quantum wires.

Enhancement type InP metal‐insulator‐semiconductor field‐effect transistors were fabricated using plasma anodic aluminium oxide as the gate insulator. The effective electron mobilities in the surface channel are 1250 cm2/Vs and 2000 cm2/Vs at 300 and 80 K, respectively. The drift of the drain current at 300 K ceases a few minutes after applying a gate voltage and stable dc operation is observed over several hours.

A new type of logic gate that can be designed using a nonhysteretic Josephson weak link is proposed. The basic component of the proposed device is a one-junction interferometer, and a logic state is represented by either a zero or a single-flux-quantum. In contrast to the "Parametric Quantron," this device is designed to operate without a three-phase clock and the dependence of the junction critical current on magnetic field is not used. The switching behavior of the device was simulated by computer and an analytical expression for the switching delay has been obtained.

Motion of a planar magnetic domain wall is calculated analytically and also simulated by a computer, and it is shown that in high driving magnetic field the wall oscillates back and fro, average drift velocity of the wall decreases, width of the wall also oscillates thin and thick and a wake of spin wave appears. The decrease of drift velocity of a planar wall in an Er-Eu-Iron Garnet crystal is experimentally observed, and is found to become 6% of the maximum velocity and to agree with the theoretical result quantitatively.

We have applied disorder-sensitive high-energy ion scattering together with the C-V method to an interface study of Al2O3/InP, which was prepared with well-controlled molecular beam deposition. Low interface state densities (the minimum value near the midgap is ∼1×1011cm-2eV-1) have been obtained in the present work. Measurements of the interface disorder for these samples suggest that there is a correlation between the interface state density and the interface disorder. It is necessary to lower the interface disorder to obtain low interface state densities.

Niobium/niobium Josephson tunnel junctions were fabricated using electron-beam evaporation of Nb films and rf-plasma oxidation. Niobium reacts easily with oxygen, resulting in a decrease in its transition temperature. In order to suppress this reaction between the tunnel barrier and the Nb counter-electrode, a thin layer of Cu was evaporated on the tunnel oxide before the Nb counter-electrode was deposited. The sub-gap current of Nb/Nb junctions with a Cu interlayer was found to be smaller than without the interlayer. Moreover, it was found that using a clean and stabilized plasma process in forming the tunnel barrier is useful in decreasing the sub-gap current of the Nb/Nb junctions.

By assuming potential clusters as one of the scattering centers for electrons in ternary alloy semiconductors, the drift mobility of electrons was calculated and compared with experimental results in (In1-xGax)As, (In1-xGax)Sb and In(As1-xPx). An explanation of the experimental results using the present model is given.

The variations in silicon wafers including standard Czochralski material, intrinsic gettered wafers, epitaxial wafers, wafers with and without backside damage, high oxygen wafers and nitrogen-doped Float Zone wafers were investigated by measuring the leakage currents of junction diodes fabricated by a modified CMOS dynamic RAM process.

1. Introduction 2. Background 3. Technological resources 4. Political context 5. Finance 6. Conclusions Appendixes Glossary of abbreviations and technical terms Notes Index.

Silicon dioxide films were grown on Si substrates by anodization in RF induced oxygen plasma at the pressure of 0.2 Torr and temperature of 600°C. SiO2 films of 1 µm in thickness were obtained within one hour. The selective oxidation was studied and Al2O3 was found to be effective in masking against the oxidation. The bird's beak shaped structure was greatly reduced.

Polycrystalline silicon accumulation-type thin-film field-effect transistors (TFTs), whose channel lengths range from 20 µm to 0.3 µm, have been fabricated, and reduction of the field-effect mobility of electrons has been observed in the lightly doped channel of submicron-gate TFTs. This phenomenon was well understood by assuming the diffusion of donor ions from the source and the drain to the channel which raised the barrier height between polycrystalline Si grains near the source and the drain. A model for device performance was built by cascading two Si TFTs with different channel doping levels. Considering that the shape of the depletion region on the surface of polycrystalline Si grains in channels is modulated by the gate voltage, the drain current-voltage characteristics were calculated, and found to be in good agreement with the experimental results.

Defect-free reactive ion etching (RIE) of silicon has been carried out using a mixture of SiF4 and Cl2 as the etching gas. The etching mechanism is investigated with a quadrupole mass spectrometer and the main reaction products are found to be Si2F6 or SiF3 for the Si etching and Si2F6O for the SiO2 etching. The deposition of (SiF2) n which occurs during the etching of silicon can be prevented by adding Cl2 gas to the SiF4. A defect-free Si surface, characterized by deep-level transient spectroscopy (DLTS), is obtained by RIE using a mixture of SiF4 (70%) and Cl2 (30%) at a pressure of 7.0 Pa with an rf power density of 0.24 W/cm2.