Showing papers in "Japanese Journal of Applied Physics in 1989"
TL;DR: In this article, the p-n junction LED using Mg-doped GaN treated with low-energy electron-beam irradiation (LEEBI) was reported for the first time.
Abstract: Distinct p-type conduction is realized with Mg-doped GaN by the low-energy electron-beam irradiation (LEEBI) treatment, and the properties of the GaN p-n junction LED are reported for the first time. It was found that the LEEBI treatment drastically lowers the resistivity and remarkably enhances the PL efficiency of MOVPE-grown Mg-doped GaN. The Hall effect measurement of this Mg-doped GaN treated with LEEBI at room temperature showed that the hole concentration is ~21016cm-3, the hole mobility is ~8 cm2/Vs and the resistivity is ~35 Ωcm. The p-n junction LED using Mg-doped GaN treated with LEEBI as the p-type material showed strong near-band-edge emission due to the hole injection from the p-layer to the n-layer at room temperature.
1,789 citations
TL;DR: In this paper, the critical current density in oxide superconductors is achieved by growing a superconducting phase unidirectionally and suppressing second phase intrusion, leading to the production of well textured YBa2Cu3Ox which yields a high Jc value in the presence of magnetic fields.
Abstract: We report a new process which promises high critical current density in oxide superconductors. The process consists of three stages. Firstly a YBa2Cu3Ox sample is rapidly heated and quenched from the Y2O3 plus liquid region. Subsequently the quenched sample is reheated to the Y2BaCuO5 plus liquid region, and then slowly cooled with a temperature gradient in flowing oxygen. The process enables us to grow a superconducting phase unidirectionally and to suppress the second phase intrusion, leading to the production of well textured YBa2Cu3Ox which yields a high Jc value in the presence of magnetic fields. It is also found that Bean's critical state is realized in such high Jc samples.
692 citations
TL;DR: The antiferroelectric structure was strongly supported by selective reflections in oblique incidence; a full-pitch band does not appear in the antiferrous liquid crystalline phases, while it does appears in the ferroelectric phase as discussed by the authors.
Abstract: At least two antiferroelectric liquid crystalline phases were discovered in MHPOBC. These phases appear below the usual ferroelectric Sm C* phase. Because of the alternation of the molecular tilt directions as well as the dipole orientations in successive layers, the optic axis is along the layer normal. This strong stabilization along the layer normal brings about the so-called third stable state responsible for the tristable switching. The antiferroelectric structure was strongly supported by selective reflections in oblique incidence; a full-pitch band does not appear in the antiferroelectric phases, while it does appear in the ferroelectric phase.
619 citations
TL;DR: In this article, the phase transition from Sm C* to Sm CA* is not observable by AC calorimetry but small peaks comparable to the Sm A-Sm C* transition are discernible in DSC.
Abstract: The phase, designated as Sm CA*, which shows tristable switching was investigated in C8H17O–--COO–-COO*CH(CH3)C6H13 (MHPOBC) by means of thermal analyses, a miscibility test and microscope observation. The phase transition from Sm C* to Sm CA* is not observable by AC calorimetry but small peaks comparable to the Sm A-Sm C* transition are discernible in DSC. According to the miscibility test of racemic MHPOBC with a standard compound, this new phase was found to exist between Sm C* and Sm I* and not to be miscible with Sm Bhex. Therefore, the assignment of Sm CA* to one of the known phases is ruled out, which means that Sm CA* is a totally new phase. The difference between the pure enantiomer and the racemate is also pointed out.
378 citations
TL;DR: In this article, the bonding speed of silicon and fused quartz wafers is measured as a function of temperature, and it is shown that the bonding process stops to operate at temperatures above 90°C and 320°C for fused quartz and bare silicon, respectively.
Abstract: The bonding speed (or contact wave velocity) of silicon and fused quartz wafers has been measured as a function of temperature. The results show that the bonding process stops to operate at temperatures above 90°C and 320°C for fused quartz and bare silicon wafers, respectively. By comparing our results to infrared spectra obtained from silica gel we develop a tentative model of the bonding process. This model is based on the assumption that the initial wafer bonding process occurs via hydrogen bonds of adsorbed water. This model explains why the bonding strength increases in two distinct steps during high temperature annealing. By introducing a phenomenological time constant τ we can also account for the fact that in an intermediate temperature range the bonding strength does not depend on annealing time as it has been reported in the literature.
274 citations
TL;DR: A mathematical framework for solving the Landau-Lifshitzitz-Gilbert equation expressed in Cartesian components of magnetization according to the backward difference method without conflicting with the constraint of constant magnetization is presented in this paper.
Abstract: A mathematical framework is presented for solving the Landau-Lifshitz-Gilbert equation expressed in Cartesian components of magnetization according to the backward difference method without conflicting with the constraint of constant magnetization. Test calculation shows that the method allows the use of a large time step almost independent of spatial mesh size and damping constant. The derived program is used to calculate the magnetization structure of a crosstie wall in a Permalloy film yielding calculated structures which closely resemble the electron-holography image of an actual cross-tie wall. It is also used to investigate magnetization reversal mechanisms in fine ferromagnetic particles by pursuing time dependent changes in magnetization structures. The paper gives detailed descriptions of the reversal mechanisms which differ depending on the size of the particle.
270 citations
TL;DR: Anodically electrodeposited iridium oxide films from alkaline solutions were investigated for application to electrochromic devices as discussed by the authors, which showed good reaction reversibility and coloration efficiency.
Abstract: Anodically electrodeposited iridium oxide films from alkaline solutions were investigated for application to electrochromic devices Micro-crystalline (diameter: 15A) films obtained by the electrolysis of aqueous alkaline solutions containing iridium chloride, oxalic acid and potassium carbonate showed good electrochromic reaction reversibility The coloration efficiency of the films was about one third that of typical evaporated tungsten oxide films, and the response rate measured by the amount of injected charge was about double The cycle lives of the cells, composed of electrodeposited films, 1M H3PO4-NaOH (pH=3~5), and an activated carbon cloth, were more than 8 × 106 with a 06 V, 1 Hz continuous square wave
237 citations
TL;DR: In this paper, the authors described the realization of wafer-scale Silicon-on-Insulator by Van der Waals wafer bonding and subsequent thinning of one of the wafers for 100 mm wafer.
Abstract: The realization of wafer-scale Silicon-on-Insulator by Van der Waals wafer bonding and subsequent thinning of one of the wafers is described for 100 mm wafers. The bonding of two silicon wafers is brought about by Van der Waals forces which are found to be sufficiently strong for a tight bond at wafer distances of less than 1 nm. This condition requires wafer surfaces which are extremely flat and free of dust particles. Usually the bonding susceptibility is enhanced by a short polishing step. Van der Waals bonding (dipole bonding) is sufficiently strong to withstand the thinning procedure, but bonding is often enhanced by an anneal step (chemical bonding) before thinning. Four thinning procedures are described: 1. Electroless chemical thinning: Selective etching of highly doped bulk material of an active wafer using an electrochemically controlled HF–HNO3–HAc–H2O etchant down to a low-dope, low etch-rate epilayer. 2. Chemical thinning: Electrochemically controlled chemical etching of p-type bulk material of an active wafer down to a p/n junction, where electrochemical passivation of an n-type silicon epilayer occurs. 3. Thinning down to a tribochemical polish stop: In this technique an active wafer is polished until grooves filled with Si3N4 are encountered. The removal rate then becomes small while SOI remains in the areas between the grooves. 4. Polish without stopper: By adapting the existing optical polishing technology, extreme control of flatness and parallelism of wafer surfaces can be achieved. It then becomes possible to polish homogeneously down to SOI layers a few microns thick over a 100 mm wafer. In procedures 1 and 2 an acceptable surface quality is obtained by applying a final tribochemical polishing step. Experimental results of the four technologies are presented. In these technologies, tribochemical polishing is crucial. The necessity of this polishing technology as an off-line facility is discussed in the broader context of ICs of the future.
201 citations
TL;DR: In this article, a polycrystalline silicon thin-film transistors (poly-Si TFT's) with a high carrier mobility were fabricated at low processing temperatures of 150 and 250°C, and they were successfully crystallized at room temperature by multistep irradiation of XeCl-308 nm excimer laser pulses without explosive evaporation of hydrogen.
Abstract: Polycrystalline silicon thin-film transistors (poly-Si TFT's) with a high carrier mobility were fabricated at low processing temperatures of 150 and 250°C. A hydrogenated amorphous silicon (a-Si:H) film was successfully crystallized at room temperature by multistep irradiation of XeCl-308 nm excimer laser pulses without explosive evaporation of hydrogen. The poly-Si TFT's fabricated by the 250°C process had a carrier mobility of 54 cm2/Vs and a low potential barrier height at a grain boundary of 0.01 eV.
196 citations
TL;DR: In this paper, a GaAs layer (2.4 µm) was grown by MBE prior to the deposition of SiO2 by P-CVD, and the results showed that cracks are observed in ELO layers due to the difference in thermal expansion coefficients between GaAs and Si.
Abstract: Epitaxial lateral overgrowth (ELO) of GaAs on a Si substrate was successfully achieved by a combination of LPE and MBE. To prevent meltback of the Si substrate by Ga solution, a thin GaAs layer (2.4 µm) was grown by MBE prior to the deposition of SiO2 by P-CVD. Uniform GaAs ELO layers with mirror surface were grown through a line-shaped window cut in SiO2 film on a Si substrate with a GaAs layer. Chemical etching with an RC-1 etchant showed that there were no etch pits observed in ELO layers except in the region just over the line seed. Although cracks are observed in ELO layers due to the difference in thermal expansion coefficients between GaAs and Si, it is concluded that this technique is promising for obtaining dislocation- free GaAs on a Si substrate.
187 citations
TL;DR: In this paper, BaTiO3 polycrystals without apparent pores or defects have been obtained under the following conditions: in 0.25~0.5 N-Ba(OH)2 solutions above 100°C under saturated vapor pressures with the current density of 10~100 mA/cm2 after 30~80 min.
Abstract: BaTiO3 thin films have been prepared in situ on Ti metal substrates by a hydrothermal electrochemical technique, where a direct current has been passed between the anode, Ti plate, and the cathode, Pt plate, in high-temperature, high-pressure Ba2+ solutions. Dense thin films, 0.1~0.3 µm thick, which consist of cubic BaTiO3 polycrystals without apparent pores or defects have been obtained under the following conditions: in 0.25~0.5 N-Ba(OH)2 solutions above 100°C under saturated vapor pressures with the current density of 10~100 mA/cm2 after 30~80 min. These films are paraelectric with the dielectric constant of ≈300.
TL;DR: In this article, the phase transitions from amorphous to crystalline states by applying electrical pulses were studied for sandwich structures of metal/GexTe100-x thin film/metal.
Abstract: The phase transitions from amorphous to crystalline states, and vice versa, by applying electrical pulses were studied for sandwich structures of metal/GexTe100-x thin film/metal. A systematic study of the crystallization temperature in GexT100-x(5\leqslant x \leqslant 30) thin films has been carried out. In some compositions, more than 104 repetitions of amorphous to crystalline states, and vice versa, were attained by the application of electric pulses. A model is proposed to explain the results observed.
TL;DR: In this article, the Schottky diodes were fabricated on boron-doped diamond epitaxial films using these contacts and investigated their properties, such as the properties of the ohmic and Schottkky properties.
Abstract: Current-voltage characteristics have been obtained for various metal contacts formed on boron-doped diamond epitaxial film prepared on synthesized Ib diamond by the microwave plasma-assisted chemical vapor deposition method. Ti contacts and W contacts have exhibited good ohmic and Schottky properties, respectively. For the first time, we have fabricated Schottky diodes on boron-doped diamond epitaxial films using these contacts and investigated their properties.
TL;DR: In this paper, the magnetization behavior of quench and melt growth (QMG)-processed YBa2Cu3O7 can be understood in terms of the critical state model.
Abstract: Magnetization measurements have been conducted on YBa2Cu3O7 samples fabricated by the quench and melt growth(QMG) technique using a vibrating sample magnetometer at 77 K. It has been found that the magnetization behavior of QMG-processed YBa2Cu3O7 can be understood in terms of Bean critical state model.
TL;DR: The optimal choice of coupling and periodicity in such systems results in miniband structures with medium width Eb and wide energy gap Eg and is found to provide a novel method to substantially reduce the optical phonon scattering of electrons in semiconductors as mentioned in this paper.
Abstract: Electronic structures in various coupled quantum box array systems including quantum-wire superlattices and planar superlattices are examined The optimal choice of coupling and periodicity in such systems results in miniband structures with medium width Eb and wide energy gap Eg and is found to provide a novel method to substantially reduce the optical phonon scattering of electrons in semiconductors Feasibility and significances of this approach are discussed
TL;DR: In this article, the metal-insulator transition driven by the change of the carrier concentration was investigated in the 80 K superconductor Bi2Sr2CaCu2O8+y.
Abstract: Metal-insulator transition driven by the change of the carrier concentration was investigated in the 80 K superconductor Bi2Sr2CaCu2O8+y. The carrier concentration was controlled by the substitution of yttrium for calcium. Experimental results from structural, transport, and magnetic studies are discussed in comparison with other high-temperature superconductor systems, La2-xSrxCuO4 and YBa2Cu3O7-y.
TL;DR: In this article, the diamond growth mechanism in C2H2/O2 flame was analyzed with laser-induced fluorescence and mass spectrometric techniques, and it was shown that CO and H2 are the dominant gases in the feather, and that C 2H2 and C-containing radicals are minor species.
Abstract: To understand the diamond growth mechanism in C2H2/O2 flame, we carried out gas analyses for various mixture ratios (R=C2H2/O2) with laser-induced fluorescence and mass spectrometric techniques. These measurements show that CO and H2 are the dominant gases in the feather, and that C2H2 and C-containing radicals (e.g., C2H, CR, Cn, n=1-3) are minor species. Their concentrations are found to be consistent with the equilibrium values estimated by the adiabatic calculation. The feather is formed by the inter-diffusion and reactions between these C-radicals and O-radicals (e.g., O and OH), which are produced in the intermediate zone by the oxidation with O2 supplied through the secondary flame. It is also found that R-dependences of the diamond growth rate is in good agreement with those of CH and C2 concentrations in the feather.
TL;DR: In this article, conductivity and band gap energy of poly(9-alkylthiophene) and poly( 9,9-dialkylfluorene) with long alkyl chains were found to be fusible at relatively low temperature.
Abstract: Conducting poly(9-alkylfluorene) and poly(9,9-dialkylfluorene) with long alkyl chains have been prepared and found to be fusible at relatively low temperature. Unlike in poly(3-alkylthiophene), electrical conductivity and band gap energy do not change remarkably at the solid-liquid phase transition. These polymers also demonstrate drastic changes of optical and electrical properties upon doping.
TL;DR: In this article, phase transitions of L- and D-enantiomers of 4-(1-methylheptyloxycalbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC) were studied by the DSC method.
Abstract: Phase transitions of L- and D-enantiomers of 4-(1-methylheptyloxycalbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC) were studied by the DSC method. Two new phases have been observed between the smectic A phase and the smectic C* phase and between the smectic C* phase and the third stable state (SY* phase) in both L- and D-MHPOBC. The new phases disappear by the introduction of more than 3% D-MHPODC into L-MHPOBC and vice versa. A phase diagram was constructed for the enantiometric mixture of L- and D-MHPOBC.
TL;DR: In this article, a Ga1-xInxN (up to X=0.42) was fabricated on sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) at 500°C.
Abstract: Epitaxial films of the solid solution Ga1-xInxN (up to X=0.42) have been fabricated on (0001) sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) at 500°C. The properties of the films have been studied by the reflection high-energy electron diffraction technique, X-ray diffraction, and electrical and optical measurements. The fundamental absorption edge of the film decreases linearly with composition (up to X=0.42) from 3.20 eV to 2.01 eV at room temperature.
TL;DR: Ferroelectric PbTiO3 thin films were prepared by a simultaneous deposition of TiO2 and PbO on heated substrates under the reduced pressure of 6 Torr.
Abstract: Ferroelectric PbTiO3 thin films were prepared by a simultaneous deposition of TiO2 and PbO on heated substrates under the reduced pressure of 6 Torr. Titanium tetraisopropoxide and tetraethyl lead were used as source materials. The deposition behaviors of TiO2 and PbO were examined independently. Homogeneous nucleations of the reaction species in the vapor phase were depressed under the reduced pressure. The films obtained at 500° to 650°C of consisted of PbTiO3 of the single perovskite phase, and highly c-axis oriented and epitaxal films were grown on MgO(100). The deposition rate of the film available by adjusting the source temperature and the flow rate of the carrier gas is 50 to 1000A/min, the maximum value of which is ten or more times that obtained by the conventional sputtering method.
TL;DR: In this paper, the number of effective positive charges generated in the SiO2 layer by a single VUV photon (Rf) is evaluated from the ΔVFB and the total VUV dose.
Abstract: Quantitative measurements of radiation damage in SiO2/Si systems induced by VUV photons generated in various microwave plasmas are performed. The SiO2/Si system is irradiated by monochromatic VUV photons, and its flat-band voltage shift (ΔVFB) is measured by the C-V method. The number of effective positive charges generated in the SiO2 layer by a single VUV photon (Rf) is evaluated from the ΔVFB and the total VUV dose. A VUV photon is found to generate effective positive charges in SiO2 when its energy (Ep) is larger than the SiO2 band gap energy (Eg=8.8 eV). The value of Rf is on the order of 10-3~10-2 and increases in proportional to the energy difference between Ep and Eg . A model is proposed to explain these phenomena. The model states that a VUV photon with energy Ep(>Eg) generates an electron-hole pair in the SiO2 and the holes that are not recombined are trapped in the energy state near the SiO2/Si interface.
TL;DR: In this article, an Al-doped ZnO film with a resistivity of 1.0 × 10-3 Ωcm was obtained at a substrate temperature of 300°C with 1.5 wt% Al2O3 content.
Abstract: Highly conductive thin films of ZnO have been prepared by conventional electron beam evaporation on glass substrates. The Al2O3 content of 0–5 wt% was added as dopant into ZnO to decrease resistivity of ZnO films. An Al-doped ZnO film with a resistivity of 1.0 × 10-3 Ωcm is obtained at a substrate temperature of 300°C with 1.0 wt% Al2O3 content; transmittance of this film is above 90% in the visible range with 100 nm thickness. The ZnO source material doped with Al2O3 is evaporated efficiently by a lower electron beam power compared to the case of nondoped ZnO. The c-axis orientation of ZnO films is facilitated by the addition of Al2O3 and the c-axis of Al-doped ZnO films is oriented perpendicular to glass substrates in the substrate temperature range of 60°C–350°C.
TL;DR: In this article, the first planar type transistor using a diamond epitaxial film has been reported, which is the first report of a planar-type transistor using diamond film.
Abstract: Metal-semiconductor field-effect transistors (MESFET's) have been fabricated on a boron-doped diamond epitaxial film. This is the first report of a planar type transistor using a diamond film.
TL;DR: In this paper, grain alignment and homogenization of the high-Tc phase (110 K) was used to increase the critical current density (Jc) and its dependence on magnetic field in Ag-sheathed Bi-Pb-Sr-Ca-Cu-O superconducting wire.
Abstract: Critical current density (Jc) and its dependence on magnetic field in Ag-sheathed Bi-Pb-Sr-Ca-Cu-O superconducting wire was improved by grain alignment and homogenization of the high-Tc phase (110 K). The maximum transport current density at 77.3 K in a zero magnetic field was increased to 6930 A/cm2. The magnetic field dependence of Jc (0.1 µV/cm criterion) was summarized as follows: 1660 A/cm2 (I ⊥H, a-b plane ∥H, 0.1 T), 900 A/cm2 (I ⊥H, a-b plane ⊥H, 0.1 T). We found that the grain boundaries were bonded strongly in the direction of alignment.
TL;DR: In this paper, the superconducting fibrous crystals of Bi(Pb)-Sr-Ca-Cu-O (2212 phase) have been prepared by heating a glassy melt-quenched plate in an oxygen atmosphere.
Abstract: The superconducting fibrous crystals of Bi(Pb)-Sr-Ca-Cu-O (2212 phase) have been prepared by heating a glassy melt-quenched plate in an oxygen atmosphere. The crystals show Tc(onset) at 75 K and Tc(end) at 70 K. The fibers have a single crystal nature and can be bent to a radius of curvature (R) of 0.4 mm without a decrease in the Tc value. The highest Jc is 67000 A/cm2 (63 K, zero magnetic field) in a nonbending state. It surpasses 35000 A/cm2 even in a bending state of R>1 mm and finally decreases down to 3200 A/cm2 for R=0.4 mm.
TL;DR: In this article, an organic ultrathin film was grown heteroepitaxially on a cleaved face of MoS2 under high vacuum of ca. 4×10-9 torr by a newly developed organic molecular beam epitaxy technique.
Abstract: Epitaxial growth of an organic ultrathin film has been confirmed for the first time by reflection high-energy electron diffraction (RHEED) during film growth. Copper phthalocyanine (CuPc) films were grown heteroepitaxially on a cleaved face of MoS2 under high vacuum of ca. 4×10-9 torr by a newly developed organic molecular beam epitaxy technique. The RHEED pattern revealed that epitaxially grown CuPc has its own lattice constant, which is completely different from that of MoS2 even at the initial deposition stage.
TL;DR: In this article, the resistivity of the diamond films was inversely proportional to the B/C ratio over four orders and the temperature dependence of current was measured and to fit this result to the theoretical calculation, the activation energy was evaluated.
Abstract: Diamond films doped with boron were fabricated by the thermal filament CVD method. Powdered B2O3 was used as the doping source. The films were identified as diamond by means of several methods including Raman spectroscopy. The resistivity of the films was inversely proportional to the B/C ratio over four orders. The temperature dependence of current was measured and to fit this result to the theoretical calculation, the activation energy was evaluated.
TL;DR: In this article, the effect of composition variation on the superconducting properties of superconductors with a nominal composition close to the ideal high-Tc phase has been investigated and it was found that deviation from the ideal composition delicately affects the Tc(0), and that even a small surplus of Ca and Cu is enough to make it lower to around 95 K.
Abstract: Superconductors with a nominal composition close to the ideal high-Tc phase, (Bi, Pb)2Sr2Ca2Cu3Oy, were prepared to study the effect of composition variation on the superconducting properties. It was found that the deviation from the ideal composition delicately affects the Tc(0), and that even a small surplus of Ca and Cu is enough to make it lower to around 95 K. In order to obtain a pure 110 K phase which allows a large current flow to yield a Tc(0) above 100 K, the composition must be strictly controlled around Sr:Ca:Cu=2:2:3 with the smallest excess of Ca and Cu. Lead was revealed to occupy Bi sites supplying positive holes to the system along with Sr defects.
TL;DR: In this paper, the influence of the Si-H2 bond on light-induced degradation and the thermal recovery of a-Si films and solar cells was studied, and an irreversible phenomenon was observed in film properties and solar cell characteristics.
Abstract: The influence of the Si-H2 bond on light-induced degradation and the thermal recovery of a-Si films and a-Si solar cells were studied. The influence of the Si-H2 bond on light-induced degradation depends on the impurity content in a-Si films, and light-induced degradation can be reduced by decreasing the Si-H2 bond density in a-Si films with impurity content of 1018 cm-3. The activation energy of the thermal recovery process was about 1.0 eV, and it did not depend on the Si-H2 bond density. However, an irreversible phenomenon was observed in film properties and solar cell characteristics with high Si-H2 bond density. It is thought that the structural flexibility of the Si-H2 bond is related to this irreversible phenomenon.