N. Shin‐ichi Takahashi

High‐speed light valve using an amorphous silicon photosensor and ferroelectric liquid crystals

A novel high‐speed response light valve composed of a hydrogenated amorphous silicon (a‐Si:H) photosensor and a chiral smectic C phase liquid crystal is presented for the first time. This device is optically addressed. The switching between on and off states is caused by reversing the polarity of the applied voltage across the liquid crystal due to the photocurrent from the a‐Si photosensor. The response time measured is about 400 μs. The switching speed of this device is one to two orders of magnitude faster than that of the nematic liquid‐crystal light valve. This device can be applied to optical bistable devices without optical feedback, using an electro‐optic memory effect of the ferroelectric liquid crystal.

New double‐heterostructure indium‐tin oxide/InGaAsP/AlGaAs surface light‐emitting diodes at 650‐nm range

New double‐heterostructure indium‐tin oxide/InGaAsP/AlGaAs surface light‐emitting diodes have been fabricated by liquid‐phase epitaxy and rf sputtering methods. In this structure, indium‐tin oxide acts as both an n‐type cladding layer and a transparent conductor. Peak wavelength and full width at half maximum of the surface emitting spectrum were 653 and 17 nm, respectively. An output power of 1 mW was achieved at a current level of 66 mA, corresponding to a current density of 22 A/cm2 under pulsed operation for the diode with a 400 μm×450 μm emitting area. The optical emission was distributed over the entire emitting area.

Fabrication methods for InGaAsP/GaAs visible laser structure with AlGaAs burying layers grown by liquid‐phase epitaxy

Liquid‐phase‐epitaxial (LPE) growth of AlGaAs layers has been used in fabricating InGaAsP buried heterostructure visible lasers on GaAs substrate. InGaAsP/InGaAsP double heterostructure wafers were grown on the p‐type GaAs substrates by means of the melt‐back method prior to the LPE growth for eliminating phosphorus contamination. An SiO2 film mask was deposited on the epitaxial wafer surface by the rf sputtering, and photoetched with stripes of 7–10 μm width in the 〈110〉 direction. After etching to the first p‐InGaAsP cladding layer with a 3% Br‐methanol solution, the second LPE growth of n‐AlGaAs and p‐GaAs layers was carried out. The InGaAsP active region is entirely surrounded by the InGaAsP cladding layers and the AlGaAs burying layer, therefore, it becomes possible to provide both lateral and vertical carrier and optical confinements. I‐L characteristics were measured at room temperature under pulsed operation, but the lasing action was not obtained. The peak wavelength of the electroluminescence was 785 nm. The transverse mode behavior was analyzed by means of the effective refractive index approximation. And it seemed that this buried heterostructure is suitable for the transverse mode control of InGaAsP visible laser diodes.

Properties of manganese-doped InGaAsP grown on GaAs substrates

In 1−x Ga x As y P 1−y (y<0,01) was grown on (100) GaAs substrate at 782 o C using manganese as a dopant. The hole concentration, resistivity, and Hall mobility of the layers as a function of Mn atomic fraction in the growth melt were reported. From the photoluminescence spectra measurements, it was found that the manganese acceptor level seemed to be rather deep

Internal loss and gain factor of InGaAsP/GaAs laser

The internal loss α and gain factor β of InGaAsP/GaAs double-heterostructure lasers were examined by immersing laser chips into various liquids and changing the reflectivities of a Fabry-Perot mirror. Only a small scatter was found; we evaluated α and β as 20.6 cm-1 and 0.0129 cmA-1, respectively. The value of α was compared with the loss of AlGaAs/GaAs lasers.

Influence of phosphorus vapor ambient for InGaAsP growth on GaAs substrate

For visible‐light‐emitting laser diodes, InGaAsP double heterostructures have been grown on GaAs substrates using liquid‐phase epitaxy. As the growth temperature is as high as about 780 °C, a large amount of phosphorus evaporates from the solutions for the cladding layers during the growth process. The phosphorus vapor disturbs the solution composition for the active layer, so that very thin and uniform active layers cannot be obtained. By using In‐P‐Sn solution and supplying the phosphorus partial pressure around the graphite boat, the influence of phosphorus vapor ambient for InGaAsP (λPL=805 nm) growth is confirmed. When the phosphorus partial pressure increases, the surface of epitaxial layer becomes rough and the substrate is partly etched back. From x‐ray diffraction and photoluminescence spectral measurements, the composition of the grown layer is also found to be changed. As a result of increasing the flow rate of H2 gas in order to protect the solution for the active layer from phosphorus contami...

Tristable Operation of Antiferroelectric Liquid Crystal Light Valves Optically Addressed Using Amorphous Silicon Photosensor

Antiferroelectric liquid crystal has recently been developed, which has three stable states and shows three levels of transmittance against the polarity of field. In this study, we have fabricated antiferroelectric liquid crystal light valves with tristable operation using the resistance change of amorphous silicon which is dependent on the intensity of input light. We have realized control of the intensity of output light at three different values as a function of intensity of input light.

n-ITO/p-InGaAsP Solar Cell Fabricated on GaAs Substrate

n-ITO/p-InGaAsP solar cells have been fabricated. Lattice-matched LPE growth of InGaAsP layers on GaAs has been carried out before the ITO film is deposited by rf sputtering. The best cell without an antireflection coating exhibits a conversion efficiency of 9.6% under AMI illumination and the corresponding open-circuit voltage, short-circuit current density, and fill factor are 0.6 V, 24.5 mA/cm2, and 0.653, respectively.

Effect of InGaAsP surface treatment for indium-tin-oxide/InGaAsP/GaAs solar cells

The performances of n‐indium‐tin‐oxide (ITO)/n‐InGaAsP/p‐GaAs solar cells in which the chemical treatment at the ITO/InGaAsP heterointerface is varied are compared: HNO3 treatment, HCl treatment, and nontreatment. The cells with HNO3 treatment show good solar‐cell performance in spite of large lattice mismatch between ITO and InGaAsP. Others do not show even rectifying behavior. The structure of the cells with HNO3 treatment is thought to be a semiconductor‐insulator‐semiconductor structure, and its current model follows the tunneling model. By Auger analysis the oxide layer, which is thought to be formed by HNO3 treatment, was ascertained. Using the heterostructure back‐surface field for the cells with HNO3 treatment, the highest efficiency attained so far is 10.9% (total area) under AM1 illumination normalized to 100 mW/cm2; the corresponding open‐circuit voltage, short‐circuit current density, and fill factor are 0.56 V, 28.8 mA/cm2, and 0.677, respectively.

AlGaInP / AlGaAs double heterostructure light emitting diode grown by liquid phase epitaxy

Abstract AlGaInP is the most promising material for visible wavelength light sources for laser-printing and audio compact disc systems. Unfortunately, it is difficult to grow controllably this crystal by conventional liquid phase epitaxy (LPE) growth, dur to the extremely large distribution coefficient of Al in the In melt. In this work, the AlGaInP layers have been grown in a very short time on an Al0.9Ga0.1As buffer layer from a non-equilibrium solution with a vey high Al fraction. The AlGaInP source melt was prepared by changing the Al mole fraction for a fixed value of Ga and P mole fractions which were for InGaP lattice-matched to GaAs. A mirror-loke surface has been obtained at an Al mole fraction X1Al between 1.96 × 10-5 and 3.21 × 10-4. Photoluminescence measurements indicated that the peak wavelength shifted to the shorter side and show that Al was incorporated into the crystals. The shortest peak wavelegth observed at room temperature was 635 nm from the AlGaInP layer grown at X1Al = 3.21 × 10-4. AlGaAs /AlGaInP / AlGaAs double heterostructure (DH) light emitting diodes (LEDs) were fabricated by this growth method with X1Al = 1.82 × 10-4. The electroluminescence (EL) emission peak at 645 nm with full width at half maximum of 66 meV was obtained at room temperature.