Masatoshi Migitaka

Optical and electrical properties of amorphous silicon films prepared by photochemical vapor deposition

Amorphous silicon films have been prepared through mercury‐photosensitized decomposition of monosilane gas at low temperatures. The films show optical and electrical properties comparable with those of the best films prepared by plasma chemical vapor deposition. The feasibility of amorphous solar cells with short‐circuit current densities of more than 10 mA/cm2 has been demonstrated by fabrication of a Schottky barrier structure.

Epitaxial growth of GaAs from thin Ga solution

Thin GaAs layers are grown by liquid‐phase epitaxy from thin Ga solutions (0.25–10 mm) using a horizontal sliding boat. The thickness of the GaAs layers is compared with theoretical values which were calculated assuming that the growth process is diffusion controlled. Numerical calculations are done on the growth rate, layer thickness, and As concentration in the Ga solution assuming a critical supercooling of 6 °C obtained by an experiment. The experimental values agreed well with the calculated values. It was found that the thickness of the GaAs epitaxial layer could be controlled by the following five growth parameters: initial temperature, initial supercooling, cooling rate, solution thickness, and growth duration.

Optical signal inverter derived from negative nonlinear absorption effects

Using a modulated laser diode, dependence of a negative nonlinear absorption effect on both the wavelength and the sample length was observed in an erbium doped yttrium aluminum garnet crystal which has a four-level energy structure. The effect was seen at wavelengths of 787.4 to 788.6 nm in excited state absorption spectra which showed a peak corresponding to the transition from 4I13/2 to 2H11/2 in Er3+ for sample lengths greater than 2.0 mm. An optical signal inverter which had a negative input-output characteristic was realized using the negative nonlinear absorption effect.

Raman scattering in low wavenumber region as a new probe to structural properties of microcrystalline silicon

Abstract The structural properties of microcrystalline silicon (μc-Si) are studied by Raman scattering. It is found that the intensity of each Raman band closely correlates with the absorption coefficient in the interband region and that the Raman band at ca. 150 cm −1 is a sensitive probe to randomness of Si-Si bonding structure in μc-Si.

1: 4 Demagnifying Electron Projection System

Reported here are the features of a 1: 4 demagnifying electron projection system, its imaging method and alignment procedures. Use of a new projection system with a small, parallel illumination beam at the mask plane plus a raster scan to cover the entire mask has made it possible to obtain high alignment accuracy as well as a large image field with a relatively small electron optical column. A linewidth of 0.5 µm and the distortion of less than 1% over an image field of 3 mm square were obtained experimentally. An alignment accuracy achieved is ±0.2 µm.

Negative Nonlinear Absorption Effect in Erbium Doped Fibers

The dependence of the negative nonlinear absorption effect on both modulation degree and modulation frequency of an incident laser was investigated in erbium-doped fibers at 77 K. Negative input-output characteristics were obtained at modulation frequencies of 10 to 250 kHz for fiber lengths above 2 m. The maximum ratio of the transmitted modulation degree to the incident one was approximately -2 for a fiber length of 4 m. It is suggested that emissions induced in the fiber can contribute to the negative nonlinear absorption effect because they propagate with low loss.

Fabrication of Submicron Pattern with an EB Lithographic System Using a Field Emission (FE) Electron Gun

This paper describes the advantages of an EB Lithographic system using an FE electron gun and steered-beam vector scan to fabricate submicron patterns. Application of this system to submicron pattern writing is studied through exposure intensity distribution (EID) and exposure dosage for submicron patterns. The system can carry out submicron pattern writing with high resolution and small proximity effect. For example, the system provides submicron resist patters with line width larger than 0.5 µm and gap spacing 1.0 µm without proximity effect correction. The application of this system to VLSI submicron pattern writing is also demonstrated.

Anomalous Properties of Silicon Recrystallized Layers Containing Indium Atoms

Experimental studies have been made on junctions prepared by alloying indium into silicon wafers. The junctions made using n‐type silicon, the resistivity of which ranges from 0.02 to 100 Ωcm, have good Ohmic characteristics, whereas the junctions made using p‐type silicon, in the range of resistivities from 0.05 to 50 Ωcm, indicate rectifying characteristics like ordinary p‐n junctions. From the measurement of thermoelectric voltages on recrystallized layers, electrical characteristics, and capacitance of the junctions, it has been concluded that the recrystallized layer containing indium atoms showed n‐type electrical conductivity. The carrier concentration in these layers is estimated to be about 1017 cm−3 near the junction side and about 1019 cm−3 near the indium dot.

20-GHz high-power GaAs DDR-IMPATT diodes with a p + -p-n-n + structure

GaAs DDR (double-drift-region)-IMPATT diodes have been made by using epitaxial wafers with a p+-p-n-n+structure, which was made by successive liquid-phase epitaxy of p+, p, and n layers on n+substrate in one heat cycle. On the diodes with copper heat sink, the maximum CW output power of 1.2 W was obtained at 21 GHz with the efficiency of 15.6 percent.

Modulation Characteristics of the Negative Nonlinear Absorption Effect in Erbium-Yttrium Aluminum Garnet

Dependence of the negative nonlinear absorption effect on both modulation degree and frequency was investigated in erbium yttrium aluminum garnet crystals. For a modulation frequency of 1 MHz, two peaks, A and B, were observed in the transmitted waveform. With a decreasing modulation degree, peak C which consists of peaks A and B appeared and a reversed-phase waveform was obtained in the transmitted waveform. Peak A decreased as the modulation frequency increased, and peak B was only observed for modulation frequencies above 50 MHz. In the case of a modulation degree under 35%, the transmitted waveform changed to the opposite phase of incident one for modulation frequencies up to 100 MHz. In addition, the negative nonlinear absorption effect was dependent on the product of the composition of erbium and the sample length. It was suggested that the enhanced absorption was due to stimulated emission in three excited states of Er3+.