Chugo Fujihashi

The quantum control limit to a single electron transistor and operation frequency improvements

The Single Electron Transistor (SET) is regarded as one of the most promising quantum devices for advanced high capacitive information systems in the future. To analyze time dependent characteristics of SET and depict factors determining the device speed, three states probability equations, which are useful and effective for practical evaluations, are suggested and solved. The quantum control limit to the maximum operation frequency of SET is evaluated from the viewpoint of the uncertainty principle between an electric charge and a magnetic flux.

Enhancement of non-geminate electron–hole pair recombination induced by strong electric field in hydrogenated amorphous silicon (a-Si:H): effective-temperature concept

Experimental evidence for field-induced enhancement of non-geminate, i.e. distant-pair (DP), recombination and shortening of the DP lifetime, τ D, by almost two orders of magnitude, is given for undoped hydrogenated amorphous silicon (a-Si:H) subjected to a strong electric field, F, up to 100 kV cm−1 at a temperature T = 3.7 K. The interplay between the T- and F-dependences of the lifetime τ D is interpreted on the basis of the effective-temperature theory developed for the high-field hopping transport of charge carriers in disordered materials at low T. The results indicate that the DP recombination event is closely connected to transport phenomena in a-Si:H.

Atom Level Header Design on Carbon Nano Tube for DNA Sequence Reader

The atom array (N, C, C, N, O) giving the hydrogen array (0, H, H, 0, 0) is presented for the header to read DNA sequence in direct. The atom array configures selective hydrogen bonds for four type molecules of an adenine, a cytosine, a thymine, and a guanine. The selective hydrogen bonds give different connectable positions in the array, and current values depending on the number of hydrogen bonds. The header probe implementing the array on the armchair type carbon nano tube is suggested for a realization.

Quadrature frequency resolved spectroscopy (QFRS) of radiative transitions of Er3+ and Nd3+ ions in chalcogenide glasses (ChGs)

Wideband quadrature frequency resolved spectroscopy (QFRS) of photoluminescence (PL) lifetime distributions from 2 ns to 160 s is shown to be very effective in elucidating the characteristic features of radiative transitions of Er3+ ions in GeGaSe and GeGaS chalcogenides glasses (ChGs). Undoped GeGaSe ChGs show triple-peak lifetime distributions of which two short-lifetimes are associated with singlet-triplet excitons and longest-lifetime, ~20 s, with radiative tunnelling (RT) of distant-pairs (DPs). Er-doped GeGaSe and GeGaS ChGs exhibit a double-peak lifetime distribution, consisting of a peak at ~3.3 and ~5.3 ms, respectively, a characteristic of the Er3+ luminescence centre and another peak at ~20 s, similar to that of undoped GeGaSe ChGs. It is shown that the QFRS can separate and analyse two mixed radiative transitions of Nd3+ ions, 4F3/2V4I15/2 and 4F5/2,2H9/2V4I15/2 in GaLaS ChGs. From the QFRS results we can experimentally extract the branching ratio ?J and lifetime ? ? 77 (?s for 4 lasing transitions 4F3/2?4IJ(J = 9/2, 11/2, 13/2, 15/2) of Nd3+ ions in GaLaS ChGs, in particular, the weakest transition 4F3/2?4I15/2.

Over-size packet accepting scheduler and optical switch design

An over-size packet accepting scheduler, while the number of the simultaneous acceptable packets is limited to one, is introduced for an output buffer type switch. An optical switch design to implement the scheduler is considered, and improvement of performance is discussed.

On introducing of state number density function for discrete energy level quantum dot transistor

Valuable progress has been made in the area of nanotechnology, but for the further advancement of atom scale devices, results and theories need to be more precise, and have a solid fundamental basis. This paper presents the improved theory in accuracy for discrete energy level quantum dot transistors. The wave packet transition model is suggested, allowing the introduction of the state number density function, and the derived results make clear why the quantum resistance based on the uncertainty principle appears in this problem. Since quantum resistance causes no energy dissipation, the relaxation process is newly considered to explain the dissipation. The potential parameters which should be applied to the quantum model of the quantum dot transistor are derived from the fundamental classical capacitance model of the transistor, and make clear the relation between the circuit voltages in the classical model and the internal potentials in the quantum model. The theory in this paper contains the orthodox theory as a special case, and the characteristics of the discrete energy level dual quantum dot transistor are analyzed.

Stochastic analysis of charging and recombination in double-hetero tunnel-junction quantum dot semiconductor laser

The double-hetero tunnel-junction quantum dot semiconductor laser model is presented in this paper to analyze a charging process by tunneling to an isolated quantum dot in an active area. The double-hetero tunnel junction structure including a small band gap quantum dot prevents tunneling transitions of electrons and holes to p and n type side areas and enhances the recombination in the dots, while a high band gap quantum dot can be used for an electron or hole current selectable transistor. A photon contained in a laser output is produced by a recombination of an electron and a hole in the quantum dot. Although the output contains many photon quanta, each charging of the electron and hole is discreet process, and the recombination is occurred in a probability manner. The laser output analysis is based on the stochastic process analysis appropriate to the treatment of the problem. The analytical solution for the probability to the charging number is given, and numerical computations of the output characteristics are presented.

Current analysis of dual quantum dot transistor based on Schrödinger equation

The specific property of the dual quantum dot transistor is that the current is strongly controlled by resonance tunneling between two quantum states in both dots. The property is analyzed clearly by the method based on Schrödinger equation for an electron in the dot and stochastic theory.

Optical MPLS shared buffer switch implementing over-size accepting scheduler

Implementation of the over-size accepting scheduler to the optical MPLS shared buffer switch and the architecture of the switch are discussed. The simulation results show that the scheduler dissolves the limitation to an acceptable packet size and improves performances.

High performance electron and hole current switching in double-hetero tunnel-junction n-i-p quantum dot transistor

A double-hetero tunnel-junction structure is introduced to the electron and hole current switching n-i-p type quantum dot transistor to improve its switching clearness. Previously the n-i-p type semiconductor quantum dot transistor was suggested on a first step model of an idea of electron and hole current switching including no recombination effect in a quantum dot and simply based on a homo tunnel-junction structure. Results in this paper show that there is some degree of recombination current in the homo tunnel-junction type and it is difficult to obtain an adequate clearness of switching performance, and newly introduced double-hetero tunnel-junction structure suppresses the recombination current and it gives a way to obtain a sufficient switching clearness.