Tsuneo Mitsuyu

Ferroelectric (Pb,La)(Zr,Ti)O3 epitaxial thin films on sapphire grown by rf-planar magnetron sputtering

Ferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) thin films have been epitaxially grown on the c plane of sapphire by rf‐planar magnetron sputtering. The sputtering conditions were investigated to obtain epitaxial and transparent films. Dielectric, piezoelectric, and electro‐optic properties of the films were measured. Piezoelectricity of the PLZT(28/0/100) film was confirmed and was as strong as that of BaTiO3. Excellent quadratic electro‐optic effects for PLZT(28/0/100) and PLZT(9/65/35) films and a linear electro‐optic effect for PLZT(21/0/100) film were observed at 0.633‐μm wavelength. Epitaxial PLZT thin film on sapphire is presently the most promising material for new functional devices.

Fabrication of long-period fiber gratings by focused irradiation of infrared femtosecond laser pulses

We have fabricated long-period fiber gratings by use of a novel technique using focused irradiation of infrared femtosecond laser pulses. We investigate the thermal stability of the fabricated fiber gratings. The values of the loss peak wavelength and the transmittance of the fiber gratings after heat treatment below 500 degrees C are the same as initial values before heat treatment. The fiber gratings that were fabricated by this technique have a high resistance to thermal decay. We propose that this technique will be useful for fabrication of fiber gratings with a superior aging characteristic.

Structures and SAW properties of rf‐sputtered single‐crystal films of ZnO on sapphire

Single‐crystal films of ZnO have been epitaxially grown on the (0001) and (0112) planes of sapphire by rf sputtering. Crystalline structures and electrical properties of the films were investigated. Surface acoustic wave (SAW) properties, including a phase velocity, a coupling coefficient, a propagation loss, and a temperature coefficient of delay, were measured for SAW propagating along the c‐axis of the ZnO films, on the (0112) planes of sapphire. Availability of this structure for high‐frequency SAW devices has been demonstrated by a filter with a 1050‐MHz center frequency.

Characteristics of Cl‐doped ZnSe layers grown by molecular‐beam epitaxy

High‐quality n‐type ZnSe layers have been grown by molecular‐beam epitaxy using chlorine (Cl) as a dopant. The Cl‐doped ZnSe layers showed mirrorlike morphology and good crystallinity, although some degrade in crystallinity is observed at a heavy doping. The carrier concentration of the layer could be widely controlled by a ZnCl2 Knudsen cell temperature. The carrier concentration attained 1×1019 cm−3, where the resistivity was as low as 3×10−3 Ω cm, indicating a remarkable improvement compared to the previous work using group‐III elements as a dopant. Hall mobilities at room temperature were in the range of 200–400 cm2/(V s), depending on the doping level. The Cl‐doped ZnSe layer exhibited strong blue near‐band‐gap photoluminescence (PL) with suppressed deep‐level emission at room temperature. The 4.2‐K PL of the layer was dominated by strong emission of excitons bound to neutral donors originating from substitutional Cl atoms. It was found by a secondary ion‐mass‐spectroscopy analysis that diffusion of ...

Characteristics of p-type ZnSe Layers Grown by Molecular Beam Epitaxy with Radical Doping

p-type ZnSe layers have been grown by molecular beam epitaxy using nitrogen radical doping. We have employed Pt as the electrode material for p-type ZnSe. The Pt electrodes markedly reduced contact resistances. The p-type conduction was confirmed by Hall measurement. Carrier concentration was 4.4×10 15 cm −3 . Hall mobility was a high as 86 cm 2 /V•s because of good crystallinity. The p-type ZnSe layers exhibited the 2.616-eV emission from recombination between free electrons and acceptor holes (FA) in room-temperature photoluminescence measurement. The FA emission provides evidence that the layers are p-type ZnSe

Space-selective growth of frequency-conversion crystals in glasses with ultrashort infrared laser pulses

We report on space-selective growth of a second-harmonic-generation beta-BaB(2)O(4) (BBO) crystal inside a BaO-Al(2)O(3)-B(2)O(3) glass sample at the focal point of an 800-nm femtosecond laser beam. A spherical heated region was formed during the focused laser irradiation through observation with an optical microscope. We moved the heated region by changing the position of the focal point of the laser beam relative to the glass sample. We grew BBO crystal continuously in the glass sample by adjusting the moving speed of the heated zone. Our results demonstrate that functional crystals can be formed three dimensionally in glasses by use of a nonresonant ultrashort pulsed laser.

Doping of nitrogen acceptors into ZnSe using a radical beam during MBE growth

A new method of doping for ZnSe was attempted by using a neutral radical beam during the MBE growth. The radical beam dominantly consisted of N2 molecular radicals at A3σ+u state. The sticking coefficient of nitrogen was remarkably enhanced; thus this doping method was able to incorporate N into ZnSe by 1019 cm−3. The existence of shallow N acceptors was confirmed by photoluminescence measurements; recombination of free electrons and acceptor holes (FA) at room temperature and recombination of donor-acceptor pairs at low-temperature were observed. The FA emission was observed only for ZnSe layers with moderate doping level, which shows p-type conduction. The carrier concentration was the order of 1015 cm−3. The activation of N in ZnSe was less than 1%.

Silicon nitride thin films prepared by the electron cyclotron resonance plasma chemical vapor deposition method

Silicon nitride thin films prepared by the electron cyclotron resonance plasma chemical vapor deposition method at low substrate temperature ( 1017 Ω⋅cm and >10 MV/cm, respectively. These properties of silicon nitride thin films are close to those of stoichiometric silicon nitride (Si3N4) prepared by the thermal chemical vapor deposition method at high temperature (>600 °C). The interface trap state density between the silicon nitride film and silicon substrate was 4×1011 cm2/eV in the silicon band gap. An optical emission spectroscopy during the deposition indicated that the intensities of nitrogen molecular ions were much stronger than those of nitrogen molecules, and the silane was sufficiently decomposed into silicon and hydrogen atoms. It is consider...

Three-Dimensional Microdrilling of Glass by Multiphoton Process and Chemical Etching

We demonstrate the three-dimensional microdrilling of glass by the multiphoton process with nonresonant femtosecond laser pulses and by the subsequent chemical etching. We use photomachinable glass which is sensitive to cw UV light of a wavelength shorter than 320 nm. After the focused irradiation of nonresonant femtosecond laser pulses at 400 nm and subsequent heat treatment, crystallites of Li2OSiO2, which are more soluble in dilute hydrofluoric acid than matrix glass, precipitate in the focused area of the laser within the glass sample. After etching the crystallites, three-dimensional holes are formed in the glass sample. We produce straight and Y-branched holes in the glass sample. This technique can be applied to the fields of microoptics, microelectronics and microchemicals.

Molecular-beam epitaxial growth of p- and n-type ZnSe homoepitaxial layers

Undoped, p- and n-type ZnSe homoepitaxial layers have been successfully grown by molecular beam epitaxy on dry-etched substrates. ZnSe substrates were etched with a BCl3 plasma to eliminate polishing damage. The full width at half maximum of an X-ray rocking curve for a homoepitaxial layer has reached 21 arc sec. N-doped ZnSe homoepitaxial layers grown with the active-nitrogen doping technique have shown p-type conduction which is the evidence of p-type conduction in ZnSe. The n-type homoepitaxial layers have been grown with Cl doping. The Cl-doped homoepitaxial layers have shown high Hall mobilities relative to heteroepitaxial layers. These undoped, N-doped and Cl-doped layers have exhibited strain-free photoluminescence properties; free exciton emission, neutral acceptor-bound exciton emission and neutral donor-bound exciton emission showed a single peaks at 2.804, 2.7931 and 2.7980 eV, respectively.