Tetsuo Morita

Maskless ion beam writing of precise doping patterns with Be and Si for molecular beam epitaxially grown multilayer GaAs

We have developed a computer‐controlled ion beam writing system with 14‐bit resolution to operate a 100 kV maskless ion implanter combined with an MBE growth chamber for patterned impurity‐doped GaAs/AlGaAs multilayer growth. Performances of various functions of this new computer‐controlled, crystal growth system have been tested. (1) Ion species (Si++, Si+, Be++, Be+) are rapidly selected with minimum astigmatism. (2) Depth impurity doping geometry can easily be controlled by automatically selecting ion charges or semiautomatically changing accelerating voltage. (3) Ion beam diameter and position are precisely monitored and controlled. (4) Ion beam mark detection can be performed with submicron resolution over double layers. (5) Ion beam writing for maskless implantation can be done in arbitrary shapes over the 400 μm square field with assigned impurity, ion dose, and energy, while monitoring ion current and beam diameter. Using this system, we have demonstrated arbitrary pattern implantation and GaAs gr...

Growth-Interrupted Interfaces in Multilayer MBE Growth of Gallium Arsenide

Growth-interrupted interfaces in Molecular Beam Epitaxy (MBE) have been characterized by C-V measurements and secondary ion mass spectroscopy. Carriers were depleted around the interfaces depending on interruption conditions such as the background vacuum and the interrupted period. For the depleted samples, carbon was detected at the interfaces. This carbon contaminant deteriorated crystal quality at the interface and caused carrier depletion. Using the MBE system combined with a maskless ion implanter in ultrahigh vacuum (UHV), a selectively Si-implanted GaAs multilayer structure was grown without interface degradation.

Fabrication of Index-Guided AlGaAs MQW Lasers by Selective Disordering Using Be Focused Ion Beam Implantation

AlGaAs multiquantum well (MQW) lasers with buried optical guide (BOG) were fabricated using Be focused ion beam (FIB) implantation. The process is based on the effect wherein the compositional disordering of Si doped MQW is suppressed by Be ion implantation and subsequent annealing. The proposed process is very simple and does not require any lithographic procedure. It is confirmed that the fabricated laser acts as an index-guided laser. This technique is a promising new step toward optoelectronic integrated circuits.

Realization of Fast InGaAs Photoconductive Response by Ion Implantation and Annealing with No Degradation of Peak Responsivity

Fast and efficient InGaAs photoconductive responses were obtained by B-ion implantation and subsequent rapid thermal annealing (RTA). Undoped, n-type (n=5×1015 / cm3), 0.5 µm thick InGaAs layers were epitaxially grown on semi-insulating InP:Fe substrates. These layers were homogeneously implanted with B ions at multiple energies. Thereafter, they were subjected to RTA in a halogen lamp furnace. The photoconductive impulse response of these layers to a 1.3 µm light pulse showed an improved FWHM (full width at half-maximum) of 0.7 ns at a dose of 1.9×1013 B/cm2 and RTA at 800°C with scarcely degraded responsivity, in contrast to the FWHM of more than 1.6 ns for original samples. It was interpreted that this improvement might be obtained due to both hole trap annihilation by the implantation itself, resulting in a removal of the long tail, and the recovery of degraded carrier mobilities by post-implantation annealing.

Fabrication of Submicron Grating Patterns Usinc Compositional Disordering of AlGaAs-GaAs Superlattices by Focused Si Ion Beam Implantation

Submicron grating patterns (0.4 µm period) were fabricated in AlGaAs-GaAs superlattices (SLs) using compositional disordering of SLs by focused Si ion beam implantation and subsequent annealing. The grating structure which is composed of preserved SL and mixed (disordered) regions was confirmed by scanning electron microscopic (SEM) and scanning Auger microscopic (SAM) observations.

Traffic congestion forecasting based on pheromone communication model for intelligent transport systems

The basic framework of next generation intelligent transport systems (ITSs) is discussed. We propose a new congestion forecast system, which reacts to dynamically changing traffic conditions based on a coordination mechanism using pheromone communication models. We evaluate and verify the basic effectiveness of this method using simple simulations.

Scan speed effects on enhanced disordering of GaAs‐AlGaAs superlattices by focused Si ion beam implantation

We studied compositional disordering of GaAs‐AlGaAs superlattices induced by focused Si ion beam implantation and subsequent annealing with different doses and scan speeds by secondary ion mass spectrometry and Rutherford backscattering spectrometry. The results indicate that the Al‐Ga intermixing is enhanced by substitutional exchange of Si‐Si pairs with vacancies as in the case of the unfocused implantation. However, with a slow scan implantation, it is confirmed that the implantation‐induced defects suppress the Si diffusion and consequently Al‐Ga interdiffusion.

Dependene of Focused Ion Beam Intensity Profile on Ion Species at Several Orders of Magnitude below the Peak Intensity

We have estimated the current intensity distribution of focused Be and Si ion beams emitted from a Au-Si-Be liquid metal ion source down to several orders of magnitude below the peak intensity. The distributions are indirectly measured from implantation-induced damage configurations formed on a GaAs by the ion beams. The diameters of the intensity distributions are more or less larger than the Gaussian profile, and they increase to several microns at six orders of magnitude below. Since the spread depends on ion species, charge, and ion emission current, the prevailing tail of velocity distribution of the FIB must be involved.

Low rate and high reliable modulation schemes for in-vehicle power line communications

In-vehicle signal transmission requires dedicated communication cables such as twisted metal wires and optical fiber cables, which increase the weight and volume of wiring harnesses in vehicles. Low rate in-vehicle power line communication (PLC) systems are investigated to communicate the control data between electronic control units (ECUs) via in-vehicle power lines. To design low rate in-vehicle PLC systems, the communication channels are analyzed. It is shown that the channels are mainly characterized by frequency selective attenuation and narrowband impulsive noise. In this paper, a model of impulsive noise is presented for in-vehicle PLC and effects of carrier frequency selection and analog limiter on narrowband impulsive noise channels are analyzed in binary phase shift keying (BPSK), differential BPSK (DBPSK), and on-off keying (OOK). The simulation results show that DBPSK and differential detection with hard limiter achieve high reliable and cost-effective communications for low rate in-vehicle PLC systems.

Interpolation System of Traffic Condition by Estimation/Learning Agents

Interpolation system of traffic condition is proposed, which consists of estimation and learning agents. To evaluate the interpolation accuracy, coefficient of determination (CD) and mean square error (MSE) are used. The interpolation accuracy can be improved by the alternate use of estimation and learning agents, and the iterative uses of the same probe data. The standard deviation of the normalized velocity can be improved to 0.1353, and that of the velocity is 6.77 km/h in the mid velocity region. Furthermore, the CD and MSE could be improved by the additional repetition of estimation and learning.