Yasuyuki Nagao

Properties of Bi12SiO20 single crystals containing first row transition metal

Abstract Single crystals of Bi 12 SiO 20 (BSO) codoped with Ga:V, Cr:P, Mn:P, Fe:P, Co:P, Ni:P, or Cu:P were prepared, and their transmission spectrum, photoconductivity, linear electro-optic effect and optical activity were studied. Distinct absorption bands are observed in the visible and near-infrared transmission spectra for the BSO containing V, Cr, Mn, Co or Cu as compared with that for the pure and P-doped BSO. Furthermore it is found that the transition metals incorporated into BSO generally quench the photoconductivity of the host crystal. Particularly, those of the BSO containing V, Cr or Cu are quenched significantly. It is also found that the incorporations of 0.15 mole% V or about 0.01 mole% (Cr, Mn, Fe, Co, Ni or Cu) do not cause important changes in the optical activity of BSO but cause small decreases in the linear electro-optic coefficients.

Low temperature metalorganic vapor phase epitaxial growth of CdxZn1−xS on GaAs

Abstract A low temperature metalorganic vapor phase epitaxial growth of Cd x Zn 1− x S on a (100) GaAs substrate was demonstrated using tertiarybutylmercaptan (t-BuSH) as a sulfur source precursor. Three other organic sulfide source precursors were also examined for comparison. By using t-BuSH, high growth rate and good composition controllability were attained in the growth temperature range from 330 to 440°C. The epilayer grown at T g = 350° C without any buffer layer between the epilayer and the substrate showed excellent crystalline properties in a wide composition range 0.53≤ x ≤0.67. n-Type doping experiments using TEIn as a dopant source were also demonstrated and doped epilayers with maximum carrier concentration of 4×10 18 cm -3 were obtained.

High External Quantum Efficiency of Electroluminescence from Photoanodized Porous Silicon

Porous silicon (PS) light emitting diodes (LEDs) were fabricated from p+n Si wafers by photoanodization. The maximum external quantum efficiency (ηext) of electroluminescence (EL) from PS-LED up to 0.8%, which is the highest ever reported for PS-LEDs with solid state contact, was achieved under pulsed operation with 1% duty in ambient air. However, we found that PS-LED with a high ηext was accompanied by the problem of high series resistance.

Dynamic Recording and Readout Characteristics of GdTbFe Using a Modified Magneto-Optical Disk Exerciser

Amorphous ternary GdTbFe alloy films with a Kerr rotation angle of 0.38°–0.41° were prepared by rf sputtering on glass disks with a diameter of 115 mm. Thermomagnetic recording and readout experiments were carried out on these disks using a modified magneto-optical disk exerciser. The bit density of a few tens Mb/cm2 and the carrier-to-noise ratio (C/N) of 38 dB at 2.048 Mb/s (NRZ) were attained. It was found that a smaller spot diameter is desirable for readout than that for recording. Furthermore, primitive measurements of bit error rate were made at 1.536 and 2.048 Mb/s (NRZ), and values of the order of 10-5 were obtained.

Metalorganic Vapor Phase Epitaxy of ZnSe Using Tertiarybutylselenol as Selenium Source Precursor

Metalorganic vapor phase epitaxy of ZnSe on a GaAs substrate was carried out using a novel organic selenium source, tertiarybutylselenol (t-BuSeH), for the first time. A constant and high growth rate was attainable in the growth temperature range of 280-500°C using t-BuSeH. The low-temperature reaction between diethylzinc and t-BuSeH was virtually eliminated, therefore growth uniformity and reproducibility were satisfactory. The grown ZnSe layers were evaluated to be of high quality by photoluminescence and X-ray diffraction measurement.

Characterization of Layered Polysilane

Layered polysilane synthesized according to a new recipe was characterized mainly by photoluminescence (PL) measurement. The PL spectrum of the as-prepared sample had a broad peak at 2.0 eV. The PL peak of a sample annealed at 300°C was also at 2.0 eV, and its PL intensity was several times greater than that of the as-prepared sample. The PL peak of a sample annealed at 400°C was red-shifted and its PL intensity was lower than those of the others. On the other hand, the PL emission from a sample rinsed in HF solution was blue-shifted and had a little lower intensity. The interpretations of the experimental results are discussed.

Epitaxial Growth of Bi12SiO20 Films by Chemical Vapor Deposition

The growth of Bi12SiO20 films on (111) Bi12SiO20 substrates has been attempted by chemical vapor deposition. With the source material combination of Bi metal and silicon alkoxide, transparent epitaxial films have been grown in the wide composition range of x=10.8–17.6, where x denotes the ratio of Bi to Si in the grown films.

Bi(12)SiO(20) thin-film spatial light modulator.

A thin-film spatial light modulator that uses an epitaxial film of Bi(12)SiO(20) has been developed. By using a thin epitaxial film as a sensing, storing, and modulating layer, we can attain high resolution of 27 line pairs/mm at 50% modulation. In addition, a novel device structure that adopts a low resistivity substrate enables this device to be erased quickly only by bias voltage switching.

Low temperature metalorganic vapor phase epitaxy of ZnSe and ZnSSe onto GaAs using tertiarybutylselenol

Abstract The metalorganic vapor phase epitaxy (MOVPE) growth of ZnSe using diethylzinc (DEZn) and tertiarybutylselenol (t-BuSeH) is described. The transition temperature from kinetically to diffusion controlled growth ( T t ) was as low as 280°C, which is the lowest value for the growth using organic selenium source precursor ever reported. The surface morphology was smoother for the layers grown at 300°C than those grown at higher temperatures. Free-excition emissions were observed for all the measured layers in 4.2 K photoluminescence (PL) spectra. However, the intensity of neutral-donor-bound exciton emissions were several times larger than that of free-exciton emissions for the layers grown at 300°C, which means there reside donor impurities in t-BuSeH. ZnSSe layers were also grown using tertiarybutylmercaptan (t-BuSH) as sulfur (S) source precursor. Although T t was 330°C for ZnS growth using DEZn and t-BuSH, the incorporation ratio of S was not drastically decreased as low as 300°C for ZnSSe due to pyrolysis enhancement by t-BuSeH.

Novel Structures for Porous Silicon Light-Emitting Diodes

In this paper, two novel structures of porous silicon (PS) light-emitting diodes (LEDs) are proposed aiming at the reduction of series resistance, Rs. The basic idea of the novel structures is to suppress the excessive growth of nanoporous silicon (nano-PS) layer that is electroluminescence- (EL-) active but highly resistive. The initial wafer of the first structure consists of a lightly-doped layer stacked on a highly-doped substrate. As a consequence of anodization, nano-PS layer is formed only in the lightly-doped layer, while meso-PS layer with moderate resistivity is formed in the highly-doped substrate. The second structure consists of alternately stacked nano- and meso-PS layers, since it is expected that multiple thin nano-PS layers connected in series are less resistive than a single thick nano-PS layer. Preliminary experimental results proved the effectiveness of these novel structures on the reduction of Rs.