Masakazu Fukai

Field-controllable liquid-crystal phase grating

A new liquid-crystal phase-grating mode has been found. The grating is formed by the application of a spatially periodic electric field to a uniformly aligned liquid-crystal layer with dielectric and optical anisotropy. The fundamental diffraction characteristics of this liquid-crystal phase grating were measured by using a Schlieren optical system, and analyzed based on Fraunhofer diffraction theory with the assumption that the refractive indices vary periodically in the liquid-crystal layer. The incident light is diffracted under the electric field in particular directions determined by the spatial frequency of the periodic electrode, and the intensity of the diffracted light increases abruptly or gradually above the threshold depending on the cell thickness. The applicability of this liquid-crystal phase grating to a light valve in a projection display system is also considered.

Self‐aligned three‐dimensional Ga1−xAlxAs structures grown by molecular beam epitaxy

Local thicknesses of a GaAs epitaxial layer grown on a mesa stripe by semiparallel Ga and As4 molecular beams have been found to be proportional to cosφGa, where φGa is a local incident angle of the Ga beam to a local crystal growing surface. Submicron‐thick three‐dimensional GaAs‐Ga1−xAlxAs multilayers have been grown self‐aligningly on corrugated structures with a 8‐μm period. The layer thicknesses and AlAs compositions (x) are also interpreted by the local incident angles of Ga and Al beams, while evidence of atom diffusion is revealed.

A high-sensitivity solid-state image sensor using a thin-film ZnSe-Zn 1-x Cd x Te heterojunction photosensor

A high-sensitivity solid-state image sensor in which a charge-transfer device is overlaid by a thin-film photoconductor for the photosensor has been developed. The scanning registers are composed of interline transfer-type bucket-brigade registers (BBD) in the imaging area and charge-coupled registers (CCD) in the horizontal scanning circuit. The special feature of this device is that the thin-film photoconductor of ZnSe-Zn1-xCdxTe heterojunction is directly formed not only on the Si-diode area but also on the scanning circuit area of BBD to obtain a high-aperture ratio. This solid-state image sensor has 506V× 413Hpicture elements and the imaging area is about 10.4V× 13.5Hmm which corresponds to that of a 1-in vidicon. High sensitivity of 0.46 µA/lx (2856 K) and large blooming control capability have been obtained by this structure. The characteristics such as sensitivity, dark current, resolution, and blooming peculiar to the structure of a solid-state imager overlaid by a photoconductor are also discussed.

Tb3+-activated In2Si2O7 phosphor

Abstract Indium silicate activated by terbium was found to be an efficient phosphor with CR excitation, the luminosity of which was comparable to the most luminous of other terbium-activated silicates. For the preparation of this phosphor, alkaline earth metal flourides proved to act as a good mineralizer. The best result was obtained when a mixture of 1 mol In 2 O 3 , 2.2 mol SiO 2 , 0.015 mol Tb 4 O 7 and 0.05 mol BaF 2 was fired at 1 400°C in air for 4 h. Other rare earth luminescent centers such as Ce, Pr, Eu, Dy, Er and Tm were examined but none showed noticeable emission. Some UV excitation properties are also described.

A CCD imager overlaid with a thin-film photodetector of a heterojunction ZnSe-Zn 1-x Cd x Te

A CCD imager which is composed of an interline transfer type scanner in the imaging area and a thin-film photodetector of a heterojunctjon ZnSe-Zn1-xCdxTe has been developed. The array consists of506^{V} \times 404^{H}picture elements. The imaging area is about6.7^{V} \times 9.0^{H}mm2in size which corresponds to that of a 2/3-in vidicon. For the device to achieve high performance, necessary conditions between the parameters of the overlaid thin-film photoconductor and the scanner have been analyzed. Blooming phenomenon is deeply related to the sensitivity. The blooming has been suppressed without sacrificing the sensitivity by applying the pulse operation of the heterojunction. As a result, excellent performances such as high sensitivity and large blooming suppression have been realized. The scene illumination if F 1.4 100 1x (S/N ratio is 46 dB for luminance signal) in a single-chip color camera. The blooming control capability is 250 times of the saturation exposure.

The heterojunction ZnSe-(Zn1−xCdxTe)1−y(In2Te3)y having high sensitivity in the visible light range and its applications

Abstract The effect of a ZnSe film on the heterostructural ZnSe-(Zn 1− x Cd x Te) 1− y (In 2 Te 3 ) y film was studied from the standpoint of crystal growth. It is made clear that the ZnSe film improves the crystallinity of the Zn 1− x Cd x Te) 1− y (In 2 Te 3 ) y film evaporated on the ZnSe film and improves the spectral sensitivity of the heterostructure in the visible to the near-infrared light range. This heterostructure which consists of many elements can be fabricated by simple evaporation and anneal methods. One of the applications of this heterostructure is the photoconductive target in a camera tube. A camera tube with such a heterostructure is called “Newvicon” and has excellent features such as high sensitivity, low dark current, no burn-in and small lag. This heterostructure can be also applied to illuminometers photometers and solid state imagers.

Blooming characteristics of a solid-state imager overlaid with a photoconductor

The control mechanisms of blooming phenomena in a solid-state imager overlaid with a photoconductor have been analyzed. The device studied is composed of an interline transfer type of scanner and a thin-film heterojunction ZnSe-Zn1-xCdxTe photoconductor. Two types of operation exist depending on the dc voltage or the pulse voltage applied to the ITO electrode on the photoconductor and it has been proved that pulse mode operation is superior to dc mode to sustain normal sensitivity under blooming suppressed condition. From the analysis of the operation it is made clear that one condition for blooming control in this device is based upon the principle of biasing the photoconductor so that in strong light the readout transistor is held in the cut-off condition except during the readout period. In the case that this condition is met, additional blooming can still occur due to the carriers excited in the Si substrate by the light that passed through the photoconductor and through the gap area between the charge collecting electrodes. By special shielding the blooming control capability can be effective up to 1100 times the saturation exposure compared to 120 times without the special shielding. The remaining blooming signal is clearly shown to be due to photo-excited carriers in the photoconductor during the blanking period.

Spectral response of ZnSe‐Zn1−xCdxTe heterojunction

The spectral response of ZnSe‐Zn1−xCdxTe (0⩽x⩽1) heterojunction is described. The heterojunction is formed by vacuum evaporation of ZnSe and Zn1−xCdxTe doped with In2Te3. The spectral response of this heterojunction is discussed for two cases, illuminated from the ZnSe side and from the Zn1−xCdxTe side. The theoretical results, based upon the assumption that the carriers excited by incident light are mainly transported by drift field, are in good agreement with the experimental results. Moreover, we could obtain a high internal quantum efficiency of 0.9 over the visible light range in this heterojunction.

A Study of Interband Scattering of Holes in Germanium

An experimental study of the cyclotron resonance of hot holes in germanium was carried out at 1.6°K making use of 6 mm microwaves. The half widths of the resonance lines for light holes, heavy holes and electrons were observed as functions of the microwave power falling on the specimen. It was found that when a large microwave power fell on the specimen, the increase in the width of the light hole line was nearly the same as that of heavy hole. This fact can reasonably be interpreted, because light and heavy holes are strongly coupled by the interband transition.

Photoconductive properties of thin-film heterojunction ZnSe-(Zn 1-x Cd x Te) 1-y (In 2 Te 3 ) y

We have developed a high quantum efficiency and a low dark current photosensor with thin-film heterojunction ZnSe-(Zn<inf>1-x</inf>Cd<inf>x</inf>Te)<inf>1-y</inf>(In<inf>2</inf>Te<inf>3</inf>)<inf>y</inf>. This heterojunction has a quantum efficiency of above 0.9 in the wavelength range of 400-750 nm and the dark current is 1.5-5.0 nA/cm²at reverse bias of about 15 V. These excellent characteristics can be obtained by adopting the blocking type heterostructure and optimizing the composition<tex>x</tex>and<tex>y</tex>. The roles of each layer of this heterojunction are analytically discussed. The ZnSe film works as a blocking layer for the holes injected from the transparent electrode, reducing the dark current. The (Zn<inf>1-x</inf>Cd<inf>x</inf>Te)<inf>1-y</inf>(In<inf>2</inf>Te<inf>3</inf>)<inf>y</inf>film is a photosensitive layer and blocks the electrons injected from this side of electrode because of its p-type conductivity. The several photoconductive properties of the heterojunction are shown to be dominated by the deep trap states lying near the middle of forbidden energy gap. This photosensor can be applied to several devices such as photocells, facsimile sensors, photoconductors for electroxerography, and photoconductive targets of camera tubes.