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In this study, the piezoelectric properties of scandium-alloyed gallium nitride (ScGaN), which is expected to be applied to microelectromechanical systems devices, are evaluated by first-principles calculations. The piezoelectric constant (d33) of GaN is found to increase by up to approximately 30 times upon the addition of 62.5 mol. % of Sc. The piezoelectric stress constant (e33) increases and the elastic constant (C33) decreases with increasing Sc content of ScGaN, driving the rise of d33. The improved piezoelectric properties of ScGaN compared with those of GaN are largely attributed to elastic softening, which is thought to be related to the transition from a wurtzite to hexagonal boron nitride (h-BN) structure driven by the change in bonding states between atoms caused by the addition of Sc to GaN. The crystal orbital Hamilton population analysis suggests that addition of Sc to GaN results in the combination of weaker Sc–N and Ga–N bonding, which makes the crystal structure unstable. This weakened bonding is thought to be the main cause of the destabilization of the wurtzite structure and transition to the h-BN structure of ScGaN. The elastic softening associated with this structural transition leads to the dramatic improvement in piezoelectric properties. [ABSTRACT FROM AUTHOR]

In this study, the switching kinetics in a (001)-out-of-plane-oriented (Al0.8Sc0.2)N thin film were systematically investigated as a function of temperature and frequency. The switching behavior followed the Kolmogorov–Avrami–Ishibashi model within the temperature and write-pulse width ranges of 300–473 K and 10 Hz–600 kHz, respectively. The switching speed increased linearly with the electric field, even at high electric fields. The frequency dependence of the coercive field (Ec) evaluated at room temperature revealed that the scaling regime of the domain-wall propagation did not transition to the flow regime, and the switching velocity of the domain increased linearly with the electric field even at high frequencies up to 600 kHz. The invariant domain-wall motion regime implies the potential of using (Al,Sc)N films for high-frequency applications. In addition, a formula for estimating the coercive field of an (Al,Sc)N film was derived by fitting the parameters obtained from the study of switching behavior. The formula indicated that the switching electric field tends to become insensitive to frequency as temperature increases. Moreover, the frequency dependency of the field was minimal even at room temperature. This is a useful index for estimating the drive voltage at the operating frequency and temperature. [ABSTRACT FROM AUTHOR]

The aim of this study is to obtain a systematic insight into the scandium (Sc) concentration dependence of the spontaneous polarization (Psp) in ScxAl1−xN by using first-principles calculations. From the calculated results, we observe that a structural change from a c-axis polarized wurtzite structure to a nonpolarized layered hexagonal structure takes place at x = 0.67, and the spontaneous polarization decreases nonlinearly with a change in the Sc concentration. Furthermore, we calculate the spontaneous polarizations from each cation individually and find that the spontaneous polarization from aluminum–nitrogen (Al–N) (P sp AlN ) is higher than that from scandium–nitrogen (Sc–N) (P sp ScN ). This difference in spontaneous polarization arising from the cationic origin is attributed to the difference in the internal parameter along the c axis (Δ u 3 k) based on the layered hexagonal structure. [ABSTRACT FROM AUTHOR]

The ferroelectricity of (Al1−xScx)N (x = 0–0.34) thin films with various thicknesses was investigated. (Al1−xScx)N films were prepared at 400 °C on (111)Pt/TiOx/SiO2/(001)Si substrates by the radio frequency dual-source reactive magnetron sputtering method using Al and Sc targets under pure N2 gas or a mixture of N2 and Ar gases. The film deposited under N2 gas showed larger remanent polarization than those under N2 + Ar mixture. Ferroelectricity was observed for films with x = 0.10–0.34 for about 140-nm-thick films deposited under N2 gas. The x = 0.22 films showed ferroelectricity down to 48 nm in thickness from the polarization–electric field curves and the positive-up-negative-down measurement. The ferroelectricity of the 9 nm-thick film also was ascertained from scanning nonlinear dielectric microscopy measurement. These results reveal that ferroelectric polarization can switch for films with much broader compositions and thicknesses than those in the previous study. [ABSTRACT FROM AUTHOR]

It is recently found that wurtzite aluminum nitride exhibits ferroelectricity by alloying with scandium. Because its remanent polarization (Pr) is large, ScxAl1−xN has attracted much attention. Gallium nitride with similar structure and properties is also expected to show ferroelectricity. Herein, ScxGa1−xN was prepared on a silicon substrate at 673 K using the sputtering method, and its ferroelectricity was investigated. Sc0.41Ga0.59N exhibited ferroelectricity before dielectric breakdown. Pr of this film, as evaluated via positive-up-negative-down (PUND) measurement, was around 120 μC/cm2, which can reduce the influence of the leakage current. This was comparable to the value of ScxAl1−xN with the same internal parameter u, which is approximately estimated from the lattice constants. Moreover, in the PUND measurement, the measurement temperature dependence of Ec was observed, which was 4.3 MV/cm at 300 K and reduced to 3.2 MV/cm at 473 K. [ABSTRACT FROM AUTHOR]

Correlations between reliability and interfacial structure changes of ultrathin silicon oxide gate films grown at 700 °C with in situ pyrolytic-gas passivation (PGP) were investigated. PGP uses a little pyrolytic N2O and NF3 during ultradry oxidation with pure O2 at less than 1 ppb humidity and has a potential for application to future low-temperature device fabrication processes due to the reliability retention of the films. It was found that the reliability for the 700 °C grown PGP films is much like that of the 800–900 °C grown ones, with an interface state density of less than 1–3×1010/eV cm2 maintained. Quantitative analyses of N, F, and O indicated that this is probably due to microscopic, interfacial structure changes, that is, N and F passivation effectively contributes to compensate inconsistent-state bonding sites and to generate a high-density structure with few dangling bonds. [ABSTRACT FROM AUTHOR]

Number densities of Si, O, N, and F atoms near the 3.5–6.5-nm-thick silicon oxide film/Si(100) interface produced by a recently proposed in-situ passivation method [pyrolitic-gas passivation (PGP)] that uses a little pyrolytic N2O and NF3 gases were determined. It was found that the generation of excess Si atoms relative to the stoichiometric SiO2 composition near the interface is effectively inhibited by the localized passivating N and F atoms. Moreover, the number of excess Si decreases while those of N and F increase with decreasing humidity. These PGP effects can be confirmed only at a humidity of less than 1 ppb. It is therefore believed that N and F passivations effectively contribute to compensate the residual inconsistent-state bonding sites near the interface that still remain through an extreme dehydration. [ABSTRACT FROM AUTHOR]

To enhance the reliability of ultrathin silicon oxide/Si(100) films and clarify the effect of fluorine on it, in situ pyrolytic-gas passivation (PGP) using NF3 was simultaneously performed with the previously proposed PGP using N2O. As a result, the following synergistic effects of F and N passivation for the films were confirmed: The electrical characteristics, such as the time-dependent dielectric breakdown lifetime, potential barrier height energy of the oxide, and interface state density, were significantly improved. Quantitative analyses of F and N indicated that this is probably caused by microscopic structural changes in the oxide near the oxide-Si(100) substrate interface. It is, therefore, believed that F passivation effectively contributes to compensate the inconsistent-state bonding sites near the interface that remain with N passivation. [ABSTRACT FROM AUTHOR]

The density and nitrogen content of 3.5-6.5-nm-thick silicon oxide films grown by ultradry oxidation using the recently proposed in situ passivation method that uses a little pyrolytic N[sub 2]O gas were determined by a charged-particle activation analysis. It was confirmed that the density increases with decreasing humidity during oxidation as well as before and exhibits a remarkable increase only at a humidity of less than 1 ppb. The humidity dependence is almost the same as that found in our previous reports, where we obtained the electrical characteristics related to the condition of the oxide-silicon substrate interface, such as the potential barrier height energy and the time-dependent dielectric breakdown lifetime. Although the binding states of the N-related bonds are still unclear, it appears that a small microscopic structural change may be brought about near the oxide-silicon substrate interface. [ABSTRACT FROM AUTHOR]

To clarify the considerable changes in the (volumetric) density ρ[sub ox] of 3.5–8.0-nm-thick silicon oxide films on Si(100) oxidized at 800–950 °C, which were confirmed by our previous work, ρ[sub ox]s and (areal) number densities of the 700–750 °C oxidation films were investigated. The ρ[sub ox]s and number densities of Si and O atoms were determined by charged-particle activation analysis and Rutherford backscattering spectrometry, respectively. It was confirmed again that excess Si atoms relative to the stoichiometric SiO[sub 2] composition exist near the oxide–Si substrate interface and the number densities of them N[sub Si(excess)]s were changed with oxidation temperature. The ρ[sub ox]s were also changed with oxidation temperature but the changes in ρ[sub ox] were diametrically contrasted with those in N[sub Si(excess)]. For the 2.0–8.0-nm-thick films oxidized at 700–950 °C, the ρ[sub ox] characteristics exhibited a maximum at 850 °C but the N[sub Si(excess)] ones exhibited a minimum at 850 °C. It is, therefore, believed that this ρ[sub ox] change is governed mainly by microscopic changes in the atomic arrangement structure due to the N[sub Si(excess)] difference. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the density of silicon oxide films grown at a desired humidity by applying charged-particle activation analysis (CPAA). Determination of the thickness of ultrathin silicon oxide films; Density of the ultrathin silicon oxide films related to humidity; Correlations between density and electrical properties.

Wurtzite gallium nitride (GaN) has a polarity along the c-axis and piezoelectric properties the same as aluminum nitride. Since it has a high mechanical quality factor and high output sensitivity, it is expected to perform well in piezo micro-electro-mechanical system devices. This paper demonstrates that Hf and Mo interlayers enable the preparation of highly (001)-oriented GaN films via conventional sputtering at a low temperature (400 °C). The piezoelectric coefficient d33 of the prepared undoped GaN films is equivalent to that of a single-crystal GaN. Furthermore, the results demonstrate that the piezoelectric response of GaN films increases significantly when they are doped with scandium (Sc). Although this enhancement was predicted theoretically, the piezoelectric response of Sc-doped GaN films prepared on Hf and Mo interlayers has shown great improvement. Moreover, bulk acoustic wave resonators constructed using Sc-doped GaN films show a piezoelectric coupling factor that is three times larger than that of a single-crystal GaN. [ABSTRACT FROM AUTHOR]

Presents a study which investigated heteroepitaxial film growth of silicon on sapphire using ionized species. Importance of low-temperature film formation techniques for the precise fabrication of highly integrated very large integration and heterostructure devices; Relationship between growth temperature and ion energy for different film growth types; Experimental procedures.

Reactions of SiHn(n=1–4) with a fluorine atom were studied by using an ab initio molecular orbital method [fourth-order Mo\ller–Plesset (MP4/6-21G**//second-order Mo\ller–Plesset MP2/6-21G**)]. Structures of the transition states were determined. In the cases of SiH3+F and SiH+F, fluorine atom addition to a silicon atom was a favorable reaction at the singlet state and abstraction of a hydrogen by a fluorine atom was a favorable route at the triplet state. Abstraction of a hydrogen was also favorable at the doublet state in the case of SiH2+F. A selection rule of these reactions on the basis of the atomic spin density on each atom was proposed. The selection rule proposed was proved to also be applicable to the reaction CH3+F. [ABSTRACT FROM AUTHOR]

Analyzes the correlation of ultradry ultrathin amorphous silicon oxide gate films with reliability. Determination of the oxidation process by charged-particle activation analysis; Relationship between reliability and density; Sample preparation for density and time-dependent dielectric breakdown measurements.

Investigates heteroepitaxial growth of 3C-silicon carbide (SiC) on silicon (Si) (111) and Si (100) by using a low-temperature crystalline film formation method, reactive-ion-beam deposition. Background on 3C-SiC; Method used to control ionized species energy; Growth using Si homoepitaxial and Si-C transition layers.

Investigates polycrystalline silicon growth on amorphous insulators by using the reactive ion beam deposition method. Types of amorphous insulators analyzed; Details of experimental procedures; Effects of growth temperature on polysilicon growth; Analysis of the effects of ion energy on polysilicon growth.

Presents a study which described a low-temperature silicon substrate surface cleaning method using a low-energy controlled ionized species produced from H[sub2] or H[sub2-]SiH[sub4] electron-cyclotron-resonance (ECR) plasma. Examples of cleaning procedures; Description of the reactive ion beam cleaning (RIBC) system used in the experiment; Reactions used to try and lower the cleaning temperature in RIBC using H[sub2] ECR plasma.

Presents a study that investigated the heteroepitaxial growth of silicon thin films on sapphire at temperature. Analysis of the film growth through a fixed ion energy; Evaluation of the growth of the thin films by accommodating the ion energy to two film growth stages; Conclusions.

Discusses a study which investigated the homoepitaxial film growth maintaining primary surface structures of silicon substrates using the reactive ion beam deposition method. Evaluation of impurity concentrations in the epitaxial films; Experimental procedures; Results and discussion; Conclusions.

We report for the first time the complete set of elastic coefficients of the mechanoluminescent material SrAl2O4 stuffed tridymite determined by the first-principles plane-wave pseudopotential total energy method. We calculate other mechanical properties (i.e., bulk modulus, Young’s modulus, and Poisson’s ratio) of this material from the elastic coefficients determined, and compare them with the corresponding experimental and calculated results of typical oxides, indicating that SrAl2O4 stuffed tridymite is a relatively soft ceramic oxide. In addition, we investigate the crystal structure of SrAl2O4 stuffed tridymite at elevated hydrostatic pressures up to 10 GPa and confirm anisotropic deformation in the SrAl2O4 lattice. [ABSTRACT FROM AUTHOR]

Presents a study which excited mixed-dye-doped solid microspheres by a transversely excited-atmospheric ultraviolet nitrogen[sub2] laser to obtain a multiple oscillation of a whispering-gallery-mode dye laser. Schematic representation of an experimental setup; Analysis of the mode structure of the emission spectra from a mixed-dye-doped polystyrene sphere.

A 20 barrel solid hydrogen pellet injector, which is able to inject 20 cylindrical pellets with a diameter and length of between 3.0 and 3.8 mm at the velocity of 1200 m/s, has been developed for the purpose of direct core fueling in LHD (Large Helical Device). The in situ pipe gun concept with the use of compact cryo-coolers enables stable operation as a fundamental facility in plasma experiments. The combination of the two types of pellet injection timing control modes, i.e., pre-programing mode and real-time control mode, allows the build-up and sustainment of high density plasma around the density limit. The pellet injector has demonstrated stable operation characteristics during the past three years of LHD experiments. [ABSTRACT FROM AUTHOR]

We report mechanoluminescence (ML) in Sm3+-doped Srn+1SnnO3n+1 (n = 1, 2, ∞) phosphors with perovskite-related structures, which consist of layered units depending on the number of n. The intensity of the ML was strongly dependent on the layered structure; the ML intensity for Sr3Sn2O7:Sm3+ was three orders of magnitude higher than that for SrSnO3:Sm3+. The charge transfer state (CTS) band in the photoluminescence excitation spectra was observed for Sr3Sn2O7:Sm3+ and Sr2SnO4:Sm3+, indicating that the efficient energy transfers from the host to the Sm3+ ions. The formation of CTS and the layered structure may be responsible for this ML enhancement. [ABSTRACT FROM AUTHOR]

The reliability of 1.5-nm-thick silicon oxide gate films grown at 150 °C by modified reactive ion beam deposition (RIBD) with in situ pyrolytic-gas passivation (PGP) using N2O and NF3 was investigated. RIBD uses low-energy-controlled reactive, ionized species and potentializes low-temperature film growth. Although the oxide films were grown at a low temperature of 150 °C, their fundamental indices of reliability, such as the time-dependent dielectric breakdown lifetime and interface state density, were almost equivalent to those of oxide films grown at 850 °C using a furnace. This is probably due to localized interfacial N and F atoms. The number density of interfacial N atoms was about seven times larger than that for the furnace-grown oxide films, and this is a key factor for improving the reliability through the compensation of residual inconsistent-state bonding sites. [ABSTRACT FROM AUTHOR]

Low-temperature ultrathin silicon oxide gate film growth using modified reactive ion beam deposition (RIBD) with an in situ pyrolytic-gas passivation (PGP) method is described. RIBD uses low-energy-controlled reactive and ionized species and potentializes low-temperature film growth. By combining RIBD with PGP using N2O and NF3, 1.5-nm-thick silicon oxide gate films with high-potential barrier height energy, 3.51 eV, and low-leakage current, less than about 10-5 A/cm2 at 2 MV/cm, can be obtained at a growth temperature of 150 °C. From an evaluation of number densities of N, F, and O atoms near the 1.5–5.0-nm-thick RIBD-with-PGP silicon oxide films/Si(100) interfaces, it is believed that interfacial N and F atoms contribute to improve the electrical characteristics and F effectively compensates the residual inconsistent-state bonding sites after the N passivation. [ABSTRACT FROM AUTHOR]

In order to investigate the ablation of a solid hydrogen pellet, which is injected into a high-temperature plasma with high speed (∼1 km/s) for the plasma refueling, a three-dimensional observation system using a fast camera has been developed. A stereo method has been employed to obtain the three-dimensional information of the pellet ablation. A pair of the stereo images, which have been taken from different locations, has been focused onto a single fast camera by using a bifurcated fiber scope to ensure the simultaneity of both images. The projection matrix, which is used for stereo reconstruction, is calibrated by taking images of a model plane of known coordinates from the actual camera positions. The measuring error of the stereo observation is within 2% in the depth direction. [ABSTRACT FROM AUTHOR]

A practical thermal oxidation system used in ultradry, ultrathin silicon oxide film growth is described. It comprises a double-wall-type fused-quartz reactor, a newly designed material-gas preheating unit, and three vacuum chambers for dehydrating and exchanging wafers. The preheating unit, used to eliminate temperature disturbances in the reactor, is assembled with a SiC composite shrouded by fused quartz and an infrared lamp heater. The temperature of material gases is quickly elevated to about 600 °C by passing them through this unit just before reaching the reactor's gas inlet. Consequently, the temperature of Si wafers in the reactor can be precisely controlled within ±0.15° at 800 °C. Moreover, the moisture concentration (humidity) in the reactor is always kept below 1 ppb. By rigorously controlling the growth temperature and ambience, high-reliability 5.0±0.05-nm-thick oxide films are obtained. [ABSTRACT FROM AUTHOR]

A reactive ion-beam deposition (RIBD) and cleaning (RIBC) system using low-temperature crystalline film growth and substrate cleaning is described. The RIBD and RIBC methods use low-energy-controlled ionized species produced from electron-cyclotron-resonance (ECR) plasma of reactive gases. The basic system comprises an ECR-type ion source allowing precise energy control of ionized species in the region of less than 500 eV and a high-vacuum cleaning and growth chamber evacuated at less than 3×10-7 Pa. Employing this system, Si substrate cleaning and high-crystalline-quality homoepitaxial film growth with superstructures on the substrates can be reliably performed at the low temperature of 650 °C. [ABSTRACT FROM AUTHOR]

A liquid metal ion source of Al with a boride reservoir was developed. In this reservoir a shorter boride emitter was designed to overcome the brittleness of boride materials and some problems in supplying the Al material. This source makes possible a long continuous operation time and enhanced reliability. The fundamental performance characteristics did not change after 250 h of operation. A stable Al ion beam emission was obtained for more than 500 h and its current fluctuation was less than ±1%/3 h for a 20–30-μA source ion current. The energy spread was less than 9 eV (FWHM) for a 30-μA/sr angular current intensity. [ABSTRACT FROM AUTHOR]

Phosphors with ultraviolet (UV) mechanoluminescence (ML) SrAl2O4:Ce (SAOCe) and SrAl2O4:Ce,Ho (SAOHoCe) were reported in this letter. The results reveal that the ML emission band is located at 375 nm similar to photoluminescent (PL) peak, which indicates that ML is emitted from the same center of Ce3+ ions as PL. Furthermore, the addition of Ho3+ increases the UV ML intensity of SAOHoCe (56 nJ/load cycle) considerably [approximately two orders of magnitude greater than that of SAOCe (0.21 nJ/load cycle)]. The formation of many shallow traps (Ho3+-e-) may be responsible for this enhancement. [ABSTRACT FROM AUTHOR]

This study prepared (1-x)BaTiO3–xCaTiO3 (x=0.20–1.0) ceramics. Their structural and electric properties were analyzed. High electrostrictive strain of 0.22%, higher by 157% as compared to BaTiO3 ceramic, was obtained near the solubility limit in the side of composite (x=0.23), which is a diphasic ceramic composed of a ferroelectric tetragonal Ba0.8Ca0.2TiO3 solid solution and a normal dielectric orthorhombic Ba0.07Ca0.93TiO3 solid solution. This enhanced electrostriction resulted from the coupling of the large ionic polarization in Ba0.07Ca0.93TiO3 with the non-180° domains in Ba0.8Ca0.2TiO3 during the external electric field exertion. [ABSTRACT FROM AUTHOR]

Elastico-deformation luminescence in strontium aluminates was investigated systematically using precisely controlled pure-phase Eu-doped strontium aluminates of SrAl12O19, Sr4Al14O25, SrAl4O7, α-SrAl2O4, β-SrAl2O4, Sr3Al2O6 and their mixed phases. This study revealed that only the α-SrAl2O4 phase produces strong elastico-deformation luminescence; other strontium aluminates show no deformation luminescence. Correlation of deformation luminescence and crystal structure was found. The α-SrAl2O4 has the lowest symmetry, crystallizing in a monoclinic structure. This finding can be applied in designing strong elastico-deformation-luminescent materials. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Elastico-deformation luminescence in strontium aluminates was investigated systematically using precisely controlled pure-phase Eu-doped strontium aluminates of SrAl12O19, Sr4Al14O25, SrAl4O7, α-SrAl2O4, β-SrAl2O4, Sr3Al2O6 and their mixed phases. This study revealed that only the α-SrAl2O4 phase produces strong elastico-deformation luminescence; other strontium aluminates show no deformation luminescence. Correlation of deformation luminescence and crystal structure was found. The α-SrAl2O4 has the lowest symmetry, crystallizing in a monoclinic structure. This finding can be applied in designing strong elastico-deformation-luminescent materials. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Properties of barium strontium titanate (Ba,Sr)TiO[SUB3] (BST) thin films, deposited by inductively-coupled-plasma (ICP)-assisted rf magnetron-plasma sputtering, were investigated. It is found that the ICP-assisted rf-magnetron plasma improved the stoichiometry of the BST film. The energy band structure of the Ru/BST/Si system was investigated. It is found that the bandgaps of BST and interface SiO[SUB2] were 4.30 and 8.95 eV, respectively, and the work function of Ru was 4.97 eV. The valence band offkets for BST/Si and interface SiO[SUB2]/Si are 3.55 and 4.48 eV, respectively. As a result, the conduction band barrier height of Ru against BST was found to be 1.40 eM. [ABSTRACT FROM AUTHOR]

The electrical prebreakdown currents in liquid and solid dielectrics under a highly nonuniform electric field condition have been measured successfully using an electro-optical current measuring system in conjunction with a 760-ns rectangular high-voltage pulse generator. The breakdown time lag was precisely measured from the current. The discharge propagation velocity was estimated from the linear relation to formative time lag and gap spacing to be 18 km/s in liquid nitrogen at +40-kV point voltage. [ABSTRACT FROM AUTHOR]

Examines the correlation between stress-induced positive charges and time-dependent dielectric breakdown (TDDB) in ultrathin silicon oxide films. Fabrication of metal-oxide-semiconductor diodes with four combinations of gate electrode and substrate type; Induction of TDDB by injection of Fowler-Nordheim tunneling electrons.

A new low-temperature film formation technique is proposed. It uses ionized species produced by an electron cyclotron resonance-type microwave ion source with reactive gases and controlled in the low ion energy region, less than about 500 eV. Good quality homoepitaxial films on Si(111) are obtained at 600 °C and 100–500 eV ion energy by using SiH4 as a material gas. By increasing the ion energy to 250-300 eV, homoepitaxial growth at 400 °C can be achieved. Polycrystalline Si films on the same type of substrates can also be obtained at 200 °C. [ABSTRACT FROM AUTHOR]

Presents whispering-gallery-mode dye lasers in blue, green, and orange regions using dye-doped, solid, small spheres. Emergence of the laser emission in all radial direction; Examination of the mode structure of the emission spectra; Exhibition of a simple periodic structure.