Tsuneo Ichiguchi

Coulomb blockade in the inversion layer of a Si metal‐oxide‐semiconductor field‐effect transistor with a dual‐gate structure

We have studied the transport properties of artificially squeezable inversion layers in a Si metal‐oxide‐semiconductor field‐effect‐transistor with a dual‐gate structure. Increasing the potential barrier height with constant intervals along the one‐dimensional channel gradually transforms a simple quantum wire into coupled quantum dots. The clear change in transport properties has been observed by changing the tunnel barrier height at low temperatures. The experimental results are discussed in terms of one‐dimensional subbands and the Coulomb blockade of single‐electron tunneling.

Power-law dissipative behavior in high-Tc superconductor

Abstract Induced voltage V in the mixed state of high- T c superconductor ErBa 2 Cu 3 O 7-x film is measured as a function of transport current I and applied magnetic field H at 77K. Both I–V characteristics and magnetoresistance exhibit similar power-law behaviors with nonuniversal exponents in the forms of V ∞ I n ( H ) and V ∞ ( H - H 0 ) m ( I ) , respectively. Response voltages to the modulated magnetic field have anomalous field-dependences nearby H = H 0 which corresponds to the lower critical field. This power-law behavior suggests that there exists a new nonlinear dissipative phase probably due to fluxiod motion.

Fabrication of Deep Sub-µm Narrow-Channe1 Si-MOSFET's with Twofold-Gate Structures

Deep sub-µm narrow-channel Si metal-oxide-semiconductor field-effect transistors (Si-MOSFFTs) are fabricated using conventional LSI processes together with electron beam lithography. The device comprises a twofold-gate structure in which a narrow gate is covered with a wide gate. With this structure, effective channel widths can be narrower than those achieved by lithography. Peak-and-valley structures are found in transconductance at low temperatures. They are thought to originate in quasi-one-dimensional subbands.

Mobility modulation in a quasi-one-dimensional Si-MOSFET with a dual-gate structure

The electrical transport characteristics of a quasi-one-dimensional Si-MOSFET with a dual-gate structure are studied. In this device, the width of the one-dimensional channel can be changed continuously using the field effect and the intervals between one-dimensional subbands as well. By making part of the channel narrower, strong oscillations in differential conductance, even negative differential conductance, have been observed at 4.2 K, indicating the enhanced modulation of the electron mobility by inter-subband scattering suppression.<<ETX>>

Magnetoresistance of multiple electron gas wires at the AlGaAs/GaAs heterointerface

A parallel arrangement of thin wires has been fabricated in the AlxGa1−xAs/GaAs heterostructure with holographic lithography. The observed anisotropy of the conductivity parallel versus perpendicular to the wires proves the existence of isolated conduction paths. Transverse magnetoresistance is negative at 4 K and exhibits a shoulder at a magnetic field, where the diameter of the cyclotron orbit amounts to 90 nm, which is supposed to be the effective wire width.

Mesoscopic transport in Si metal‐oxide‐semiconductor field‐effect transistors with a dual‐gate structure

This article studies the mesoscopic transport of electrically controllable inversion layers of Si metal‐oxide‐semiconductor field‐effect transistors that use a dual‐gate structure. We have developed two kinds of devices: a quasi‐one‐dimensional device (1D‐FET) and a Coulomb blockade device (CB‐FET). In both devices, the field effect is used to change the channel structure by introducing potential barriers in the narrow inversion channel. The 1D‐FET changes a long diffusive quantum wire into a short ballistic one. Strong oscillations in differential conductance, even negative differential conductance, have been observed at 4.2 K, indicating enhanced modulation of electron mobility by intersubband scattering suppression. The CB‐FET, on the other hand, transforms a simple quantum wire into a coupled quantum‐dot array. A clear change in transport properties is observed with changes in the barrier height at low temperatures. The experimental results are consistent with the theory of one‐dimensional subbands an...

Si resonance transport device

A novel Si quantum device having controlled one-dimensional subbands was characterized experimentally in detail. In this device, the resonance transport effect between 1D subbands which are formed by dual layer gates is used as the device operating principle. The lower narrow gate produces the quantum conductive channel (quantum wire) with 1D subbands. The upper gate can change the effective channel width by applying negative bias, resulting in modulation of the transport characteristics. At 4.2 K, transconductance is found to show oscillatory behavior and negative differential resistance, which implies that resonance transport indeed occurs. It is suggested that resonance transport effects in Si will trigger new ULSI applications such as multifunctional circuits in the sub 0.1 mu m era.<<ETX>>

Rectification of Millimeter Waves in Nanometer-Scale Si-Inversion-Layer Metal-Oxide-Semiconductor Field-Effect Transistors

We measured the millimeter wave response of nanometer-scale Si metal-oxide-semiconductor field-effect transistors (Si-MOSFETs) between 1.8 K and 4.2 K, which showed irregular conductance oscillation versus gate voltage and nonlinear I–V characteristics, which we attributed to hopping conduction between localized states. Sign-changeable rectified current of 75 GHz millimeter waves was observed, and the peak positions in plots of rectified current versus gate voltage coincided with those of conductance oscillation. The rectification occurred even when electrons were heated considerably by millimeter waves. The rectification was also explained in terms of a hopping regime.

Two-Dimensional Phase Fluctuation in High-T c Superconductor under Magnetic Field

Two kinds of power laws, V∝I n(T,H) and V∝H m(T, I), are observed in high Tc superconducting ErBa2Cu3 O7 - x films. The Nelson-Kosterlitz jumps and the related new kinks are found in the temperature dependences of the respective exponents n and m, giving direct evidences of the Kosterlitz-Thouless transition. These behaviors are the results of vortex-antivortex pair excitation caused by the phase fluctuation on the each CuO2 plane. Dynamics of the pair excitation is turned out to be strongly affected by an applied magnetic field. The observed power laws in a magnetic field with an arbitrary direction suggest that the pair excitation in a magnetic field is related to the flux entanglemant state.

Microstructures and Superconductivities of LnBa2Cu3O7-x Thin Films

YBa2Cu3O7-x and ErBa2Cu3O7-x thin films are deposited on SrTiO3 and MgO single crystal substrates by rf-magnetron sputtering. YBa2Cu3Ob-x film is grown epitaxially on SrTiO3 substrate. ErBa2Cu3O7-x film is highly c-axis oriented perpendicular to MgO substrate. A lot of twins on a-b plane are observed by TEM. Jc seems to be affected by the subgrain defects rather than by the twin defects. The critical current dependency on the direction of applied magnetic field is also studied. Twin boundaries are thought not to be strong pinning centers of magnetic flux. Crystallographic anisotropy of oxygen-defect perovskite contributes to flux pinning.