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Deep-ultraviolet (UV) light-emitting diodes (LEDs) based on AlGaN crystals have low light-emission efficiency; therefore, there is a need to improve this light-emission efficiency for a wide range of applications such as water and air sterilizations. UV-light-transparent device structures are considered one of the many solutions toward increasing light output power. To this end, the present study focused on developing a transparent AlGaN-based tunnel junction (TJ) as the anode of a deep-UV LED. Deep-UV LEDs composed of n+/p+-type AlGaN TJs were fabricated under the growth condition that reduced the carrier compensation in the n+-type AlGaN layers. The operating voltage was 10.8 V under the direct current (DC) operation of 63 A/cm2. In addition, magnesium zinc oxide (MgZnO)/Al reflective electrodes were fabricated to enhance the output power of the AlGaN homoepitaxial TJ LED. The output power was 57.3 mW under a DC operation of 63 A/cm2, and it was 1.7 times higher than that realized using the conventional Ti/Al electrodes. The combination of the AlGaN-based TJ and MgZnO/Al reflective contact allows further improvement of the light output power. This study confirms that the AlGaN TJ is a promising UV-transmittance structure that can obtain a high light-extraction efficiency.

Stimuli-responsive polymeric nanoparticles (NPs) exhibit reversible changes in the dispersion or aggregation state in response to external stimuli. In this context, we designed and synthesized core-shell NPs with threonine-containing weak polyelectrolyte shells and fluorescent cross-linked cores, which are applicable for the detection of pH changes and amine compounds in aqueous solution. Stable and uniform NP(dTh) and NP(Fl), consisting of fluorescent symmetric diphenyl dithiophene (dTh) and diphenyl fluorene (Fl) cross-linked cores, were prepared by site-selective Suzuki coupling reactions in self-assembled block copolymer. NP(Fl) with the Fl unit in the core showed a high fluorescence intensity in different solvents, which is regarded as an aggregation-induced emission-type NP showing strong emission in aggregated states in the cross-linked core. Unimodal NPs were observed in water at different pH values, and the diameter of NP(Fl) changed from 122 (pH = 2) to 220 nm (pH = 11). Furthermore, pH-dependent changes of the fluorescence peak positions and intensities were detected, which may be due to the core aggregation derived from the deprotonation of the threonine-based shell fragment. Specific interactions between the threonine-based shell of NP(Fl) and amine compounds (triethylamine and p-phenylenediamine) resulted in fluorescence quenching, suggesting the feasibility of fluorescent amine detection.

The effective mobility in 4H-SiC trench metal-oxidesemiconductor field-effect transistors (MOSFETs) with an n-channel region on the 1 1 - 00 face, corresponding to the trench sidewalls, is investigated. Using a previously proposed mobility model, which includes Coulomb scattering mobility ( μ C ), surface roughness scattering mobility ( μ S R ) and optical phonon scattering mobility ( μ O P ), the dependence of the effective field (Eeff) on μ O P is studied experimentally. It is found that for the trench MOSFETs with a drift layer, μ O P is proportional to Eeff−1, whereas for trench MOSFET without a drift layer, it is proportional to Eeff−0.3, which is consistent with reports on phonon scattering mobility in SiC lateral MOSFETs fabricated on 0001 and 000 1 - faces. The results suggest that the proposed mobility model is effective, and that the dependence of Eeff on μ O P is not affected by the plane orientation of SiC and needs to be evaluated with the drift layer resistance removed. A method for evaluating the carrier transport properties of trench MOSFETs with a drift layer is also proposed.

P-type doping in selected areas of gallium nitride (GaN) using magnesium (Mg)-ion implantation and subsequent ultra-high-pressure annealing (UHPA) are investigated to improve the performance of vertical GaN power devices. UHPA allows a high-temperature process without decomposition of the GaN surface and virtually complete activation of the implanted Mg ions in GaN. In the present paper, we provide an overview of recent challenges in making UHPA more realistic as an industrial process. Instead of UHPA at more than 1400 °C for a short duration, prolonged UHPA at 1300 °C demonstrates a comparable acceptor activation of Mg-ion-implanted GaN. This can reduce the annealing pressure to approximately 300 MPa and enlarge the processable wafer diameter. The second challenge is controlling the doping profiles in the lateral and vertical directions. We demonstrate fine patterning of the p-type regions, which indicates the limited lateral diffusion of Mg through UHPA. However, controlling the vertical doping profile is challenging. The nitrogen vacancies formed by ion implantation reduce the effective acceptor concentration near the surface, which can be compensated for by sequential nitrogen ion implantation. Defect-assisted Mg diffusion to the deeper region causes a redistribution of the Mg atoms and should be considered in the design of a device. Such anisotropic diffusion of Mg to the c-axis has potential applications in the fabrication of unique vertical device structures such as super junctions.

In this study, we clarify the impact of annealing pressure and temperature of the ultra-high-pressure annealing (UHPA) as a post-implantation-annealing (PIA) on the acceptor activation for Mg-ions-implanted GaN samples. The pressure to prevent the thermal decomposition is absolutely determined by the equilibrium N 2 partial pressure in the phase diagram of GaN-Ga-N 2 system, so that the pressure below the critical pressure always leads to the serious surface decomposition of GaN. In low temperature cathodoluminescence examinations, the samples processed at 1400°C or above exhibited more intense emissions in the near band edge and donor-acceptor pair band with a suppression of green luminescence related to point defects. Temperature dependent Hall-effect measurement was allowed for the UHPA samples annealed at 1400°C or above, whereas free holes were not observed for the 1300°C-UHPA. Moreover, the acceptor concentrations (N a ) for samples annealed at 1400°C or above were close to Mg concentrations. We thus revealed the key process parameters in UHPA, which is at more than 1400°C under the N 2 overpressure exceeding the equilibrium partial pressure. These findings can play as a key role in the selective area doping using UHPA.

The atomic structure of nitrogen at the SiO2/4H-SiC(0001) interface has been investigated using X-ray absorption spectroscopy (XAS) in two nitric oxide annealed samples, one of which was oxidized in dry O2(NO-POA) prior to the experiment. The peak shapes and energies of the observed and simulated spectra are in agreement and indicate that the N-containing sites could be the substitutional C site at the interface for the NO-annealed sample and the interstitial site in the interior of SiC for the NO–POA-annealed sample. XAS analysis distinguished between the N-containing sites at the SiO2/SiC interface.

This paper describes the self-assembled fabrication of single-crystal GaN with a bimodal pore (meso/macropore) size distribution (BiPS-GaN). A 4.7 μm-thick BiPS-GaN layer was grown spontaneously using halogen-free vapor phase epitaxy in conjunction with boron impurity doping (>1 × 1019 atoms/cm3) on a GaN template fabricated via metalorganic chemical vapor deposition (MOCVD-GaN). The boron impurity acted as a surfactant, and its segregation generated a dense (>1 × 1010 cm–2), homogeneous distribution of mesopores with sizes of 30–40 nm in GaN during growth. In addition, macropores with sizes of 0.1–2 μm were produced by the fusion of mesopores in close proximity to one another. As a result, BiPS-GaN exhibited a high density of both meso- and macropores, all aligned in the vertical direction (that is, along the c axis). BiPS-GaN showed good electroconductivity and almost the same high degree of crystallinity as the MOCVD-GaN template. Furthermore, the hybrid meso/macropore structure of BiPS-GaN imparted ex...

Although halogen-free vapor-phase epitaxy (HF-VPE) is suitable for GaN bulk-crystal growth, the macrodefects (hexagonal and embedded hexagonal pits) have been observed on the as-grown surfaces of HF-VPE GaN layers. In this study, the formation mechanism of these defects is clarified using a combination of scanning transmission electron microscopy, cathodeluminescence, and three-dimensional atom-probe tomography. These analyses indicated that the formation mechanisms of both hexagonal and embedded hexagonal pits were related to the dislocations, and the hexagonal pit was identified as a hollow-core super dislocation. Moreover, some of hollow-core dislocations might dissociate into multiple closed-core elementary dislocations, as a result the embedded hexagonal pits were formed. These dislocations are generated by misoriented GaN on the regrowth interface owing to an unintentional Ga vapor supply at the initial stage of HF-VPE regrowth. To suppress the dislocation generation at the regrowth interface, growth conditions are optimized at the initial growth stage; thereby, the optimized HF-VPE-GaN layer exhibits no hexagonal pits on the grown front. The full widths at half maximum of the ω-scan X-ray rocking curves at the optimized HF-VPE-GaN layer were almost the same as those of the underlying GaN substrate. Thus, we could grow macrodefect-free and low-dislocation-density homoepitaxial thick (∼100 μm) GaN layers at a growth rate of ∼160 μm/h on a native GaN substrate.

We demonstrate the advantage of post-implantation annealing (PIA) in NH3/N2 for a p-n diode (PND) fabricated by the implantation of Mg and N ions into an n-type GaN layer by comparison with that annealed in N2. The leakage current for the PND with a reverse bias was lower in the case of NH3/N2 annealing. The cathodoluminescence spectrum measured for NH3/N2 annealing indicated a reduction in the densities of non-radiative recombination centers and nitrogen vacancy complexes. PIA in NH3/N2 is thus effective to suppress the density of implantation induced defects as leakage current sources.

GaN is a promising material for power semiconductor devices used in next-generation vehicles. Its electrical properties such as carrier mobility and threshold voltage are affected by the interface between the oxide and the semiconductor, and identifying the interface states is important to improve these properties. A surface-sensitive measurement of Ga K-edge extended X-ray absorption fine structure (EXAFS) by detecting Ga LMM Auger electrons that originate from Ga K-shell absorption is proposed for GaN. LMM Auger electrons with low energies were detected and the EXAFS oscillation was confirmed, providing information on the Ga atoms at the surface. Investigation of thermally oxidized GaN with an oxide film of defined thickness showed that the analysis depth was less than 10 nm, which is consistent with the inelastic mean free path of 2.3 nm estimated for LMM Auger electrons in GaN.

For the solution to global energy issues, highly-efficient energy conversion using next-generation power devices is required. Gallium nitride (GaN) having superior properties such as high breakdown electric field (2.8–3.75 MV/cm) is a powerful candidate for next-generation high-power semiconductor devices. [1] , [2] The selective area doping makes it possible to precisely engineer high-power devices with complex structures, allowing formation of low-resistivity region for contacting electrodes and optimization of the electric field configuration in the edge termination represented by the field limiting ring (FLR) and in the junction barrier Schottky (JBS) structures, as used in Si and SiC power devices. [3]

AlGaN-based ultraviolet light-emitting diodes (UV-LEDs) are key components for the inactivation of viruses. Highly efficient and high-power UV-LEDs, capable of inactivating viruses in a short time, are in demand. For this purpose, the growth technologies of n-type AlGaN contact layers were developed from two points of view: first, to decrease the resistivity of n-type Al0.62Ga0.38N by minimizing the electron compensation, resulting in electronic degeneracy with metallic conduction;second, to improve the light emission uniformity in AlGaN multiquantum wells (MQWs) by controlling the morphology of the underlying n-type AlGaN layer to inhibit macrostep formation. A UV-LED module emitting at 275 nm was demonstrated with the developed growth technology, and illuminated with an irradiation power of 2.6 mW cm(-2) on SARS-CoV-2 samples. Over 99.999 % of viruses were inactivated within 5 s owing to the high power of this module.

Fe2O3-based photocathodes are one of the least expensive options for hydrogen generation by water splitting. Although p-type N,Zn-doped Fe2O3 (N,Zn–Fe2O3) has been reported to possess a negative conduction band minimum position sufficient for photocathodic hydrogen generation, the efficiency and stability of the resulting H2 production is low and the reaction is sacrificial. In the present work, analysis by hard X-ray photoelectron spectroscopy (HAXPES) showed that these negative characteristics result from the self-redox reaction of p-type Fe2O3. Based on this result, a TiO2 layer was introduced onto the surface of p-type N,Zn–Fe2O3 to passivate surface defects. In addition, to ensure efficient electron transfer, a thin Cr2O3 layer was also inserted between N,Zn–Fe2O3 and a bottom side conductive oxide layer to generate a favorable band alignment for hole transfer. The resulting Pt/TiO2/N,Zn–Fe2O3/Cr2O3 electrode exhibits a highly stable, significantly enhanced cathodic photocurrent during H2 production under AM 1.5 irradiation. The mechanism providing this improvement was investigated by combining electrochemical impedance spectroscopy, open-circuit voltage decay analysis and scanning tunneling electron microscopy-energy dispersive X-ray spectroscopy. Stoichiometric water splitting without an external electrical bias was also demonstrated by connecting the Fe2O3-based photocathode to an n-type SrTiO3−x photoanode, representing the first-ever example of stoichiometric overall water splitting using an Fe-based photocathode.

Electronic degeneracy to express metallic conduction in Al-rich AlGaN for the electron injection layer enhances the efficiencies of deep ultraviolet light emitters. This study systematically demonstrates the Si doping range and conditions to realize degenerate n-type Al0.6Ga0.4N layers based on the electron compensation effect. The temperature-independent electron concentrations resulting from the degenerate band appear in high Si doping conditions to overcome the electron compensation due to carbon on nitrogen sites (CN). However, excessive Si doping of over 4.0 × 1019 cm−3 leads to the collapse of the electronic degeneracy and a switch to the temperature-dependent electron transport via the impurity bands, where the luminescence bands originating from III vacancy-Si complexes (VIII-nSi) are dominant. The key parameter is the effective donor concentration, Nd − Na, based on the reduction in electron concentrations via acceptor-like deep levels such as CN and VIII-nSi. The Hall-effect analyses for n-type Al0.6Ga0.4N layers with various Si concentrations yielded an Nd − Na value of (9.5 ± 2.9) × 1018 cm−3 to vanish the ionization energy of Si donors, which is approximately six times higher than that in GaN. The results suggest not only the optimal doping range to obtain an Al-rich AlGaN layer with metallic conduction but also the necessity of the growth condition to minimize electron compensation.

Defect time-evolution was investigated in Mg ion-implanted GaN after annealing at 1573 K for an unprecedentedly long duration. Transmission electron microscopy directly revealed that annealing for over 30 min reduced defects inhibiting Mg activation, just like annealing at 1753 K for a short duration. The cathodoluminescence intensity of donor–acceptor pair originating from Mg acceptors increased as the duration increased, and the intensity after annealing for 60 min was higher than after short-duration annealing at 1753 K. These show the potential of lowering the annealing temperature by prolonging the duration, which would lead to practical annealing technology for Mg ion-implanted GaN.

The fabrication processes of p-type regions for vertical GaN power devices are investigated. A p-type body layer in a trench gate metal-oxide-semiconductor field-effect transistor requires precise control of the effective acceptor concentration, which is equal to the difference between the Mg acceptor concentration (Na) and the compensating donor concentration (Nd). The carbon atoms incorporated during growth via metalorganic vapor phase epitaxy substitute nitrogen sites (CN) and function as donor sources in a p-type GaN layer. Since interstitial H atoms ( H i ) also compensate holes, their removal from an Mg-doped layer is crucial. Extended anneals to release H atoms cause the formation of extra hole traps. The p+ capping layer allows effective and rapid removal of H atoms from a p-type body layer owing to the electric field across the p+/p– junction. On the other hand, selective area p-type doping via Mg ion implantation is needed to control the electrical field distribution at the device edge. Ultrahigh-pressure annealing (UHPA) under a nitrogen pressure of 1 GPa enables post-implantation annealing up to 1753 K without thermal decomposition. Cathodoluminescence spectra and Hall-effect measurements suggest that the acceptor activation ratio improves dramatically by annealing above 1673 K as compared to annealing at up to 1573 K. High-temperature UHPA also induces Mg atom diffusion. We demonstrate that vacancy diffusion and the introduction of H atoms from the UHPA ambient play a key role in the redistribution of Mg atoms.

Ion implantation (I/I) and annealing techniques to enable high carrier doping into selected regions are one of important research fields for realization of GaN power devices. However, particularly difficult research challenges are present in Mg-I/I into GaN as p-type doping technique. First problem is related to nitrogen vacancies (VN), crystal defects introduced by Mg-I/I . [1] Second issue is connected to degeneration of GaN surface by pyrolysis reaction during high-temperature annealing process. We examined Mg/N co-implantation into GaN as p-doping in order to compensate of VN defects. Research on ultra-high pressure thermal activation process to maintain equilibrium conditions at high temperature was conducted to avoid degradation of GaN surface. We prepared Mg/N co-implanted GaN-on-GaN samples with 300-nm-deep Mg-box-profile of 1E19 cm-3 and with N-box-profile of various concentrations in the range 0 ~ 1E20 cm-3. The samples were annealed without a protection cap layer at temperature between 1300 °C and 1480 °C under 1 GPa in N2 atmosphere. Samples capped with sputter-AlN were treated by conventional lamp annealing at 1300 °C for a comparison purpose. We obtained the dominant Green Luminescence (GL) emission at 2.3 eV and the recessive Donor Acceptor Pair (DAP) emission at 3.2 eV from a low-temperature cathodoluminescence (LT-CL) spectra in Mg-I/I samples without N co-implantation. This is in good agreement with results published before.[1][2] In addition to this, we found that the Mg/N co-implantation, for optimized N-ion dose, suppresses the GL intensity while maintaining the DAP intensity. Furthermore, in the ultra-high pressure thermal activation process, the DAP intensity markedly increases with anneal temperature and GL intensity suppression is also visible. These results strongly suggest that the origin of GL is related to VN, and the VN defect compensation occurs by N co-implantation. We also compare the AFM images of GaN surface roughness. The ultra-high pressure annealed surfaces were as smooth (RMS = 0.2~0.3 nm) as the as-implanted samples (0.3 nm), whereas surface treated with conventional lamp was rough (1.9 nm). We can, therefore, conclude that Mg/N co-implantation and ultra-high pressure thermal activation process allows activation of the Mg acceptor and recovery of p-GaN crystal quality. Such treatment results in VN defect compensation and a smooth surface of the annealed sample. This work was supported by MEXT “Program for research and development of next-generation semiconductor to realize energy-saving society.” [1] A. Uedono et al., Phys. Status Solidi B 252, No. 12 (2015) [2] K. Kojima et al., Appl. Phys. Express 10, 061002 (2017).

The atomic structure of nitrogen at the SiO

This paper describes the observation of band bending and band edge shifts at the interfaces between nanoscale metals and TiO2 film over a wide depth range by angular-resolved hard X-ray photoemission spectroscopy (HAXPES). The HAXPES results indicate strong electrostatic interactions between the TiO2 semiconductor and metal nanoparticles, while density functional theory (DFT) calculations suggest that these interactions are primarily associated with charge transfer leading to electric dipole moments at the interface in the ground state. The effects of these dipole moments are not limited to the surface but also occur deep in the bulk of the semiconductor, and are highly dependent on the coverage of the metal nanoparticles on the semiconductor species.

Ion implantation technique for controlling n- or p-type conduction has been a significant challenge for GaN-based high-power devices to achieve levels approaching their theoretical limits of performance. Previous studies on n-type conduction of GaN through Si ion implantation achieved 86% [1] and approximately 100% [2] of activation rate after annealing at 1250 and 1400 °C, respectively. Such high-temperature annealing results in serious surface degradation of GaN(0001) due to decomposition [1], thereby needing a protective layer. However, it is difficult to make a proper choice of a protective layer which remains unaltered and is removable after annealing above 1200°C. Therefore achieving the high-activation rate at lower temperature is a very important practice. On the other hand, the Mg-ion implantation for p-type conductivity is more challenging due to the higher-temperature annealing required for electrical activation, resulting in a major difficulty protecting the surface. The formation energy of Mg on the Ga site (Mg Ga ) at the position of Fermi level near the valence band is about 1 eV higher than that of Si Ga at the Fermi level near the conduction band [4, 5], which may explain the difference of required annealing temperature for different conduction types.

Defects in Mg ion-implanted GaN epitaxial layers formed after annealing at 1573 K and at 1753 K were analyzed by transmission electron microscopy. Degradation of the GaN surface, which occurs at temperatures higher than about 1573 K, was avoided by ultra-high-pressure annealing under a N2 atmosphere at 1 GPa. Annealing for damage recovery in ion-implanted compound semiconductors generally requires temperatures at about two-thirds of their melting point, which is reportedly 2518 K or higher for GaN. Thus, defect analysis in ion-implanted GaN annealed at temperatures higher than 1573 K is necessary to understand the defect recovery. Atomic-resolution transmission electron microscopy analysis showed that interstitial-type extended defects and inversion domains with Mg segregation were formed during the annealing at 1573 K. These defects were not observed in a sample annealed at 1753 K; instead, vacancy-type extended defects were formed. Such evolution of defects can be explained by previous theoretical studies that indicated that the migration energy of vacancy-type defects is higher than that of interstitial-type defects. Moreover, the formation of vacancy-type extended defects implies a reduction in the concentrations of vacancies and their complexes. Since the vacancies and their complexes can compensate for Mg acceptors, their reduced concentration should increase the acceptor activation efficiency. Also, the disappearance of Mg segregation during high-temperature annealing should increase the activation efficiency since the segregated Mg atoms are electrically inactive. It is thus concluded that the evolution of defects caused by high-temperature annealing above 1573 K increases the activation efficiency of acceptors in Mg ion-implanted GaN.

The formation mechanism of Ga-rich streaks in the AlGaN layers formed at macro-step edges was investigated by analyzing AlGaN layers grown by metalorganic vapor phase epitaxy on AlN/sapphire-templates. Energy dispersive X-ray spectroscopy in the cross-sectional scanning transmission electron microscopy revealed that the macro-steps formed during AlN growth were maintained through the upper AlGaN layer. This can be explained by the less interaction between adjacent macro-steps due to the sufficiently smaller surface diffusion lengths of Ga and Al species than the inter-macro-step distance of submicron to a few microns. Moreover, atomic force microscopy indicated that the apparent smooth region between macro-steps involved many atomic steps and terrace width of a few ten nanometers which may be the actual scale of the diffusion lengths. At the macro-step edge, facets that are different from a c-plane are formed. The higher incorporation efficiency of Ga atoms on these facets compared with that of the c-plane likely led to the formation of Ga-rich streaks due to the less inter-surface diffusion between the facets and c-plane regions. We demonstrated AlGaN growth without Ga-rich streaks using the flattened AlN/sapphire-template by polishing; this resulted in the achievement of homogeneous emission energies in AlGaN-based quantum wells.

Etching damage induced by inductively coupled plasma (ICP) with a mixture of Cl and BCl gases and the effect of subsequent annealing in Nwere studied through positron annihilation and cathodoluminescence (CL) for Mg-doped and Si-doped GaN. The changes in the concentration of nonradiative defects and in the shape of band bending caused by ICP etching or subsequent annealing were studied by comparing the CL intensities and the diffusion lengths of implanted positrons, respectively. For Mg-doped GaN, CL spectra revealed that etching inactivated the Mg acceptors at the near-surface region. After annealing at 900 °C, the Mg acceptors were reactivated. For Si-doped GaN, etching introduced neutral vacancy-type defects, and after annealing at 900 °C, the etching-induced defects almost disappeared. However, there were residual nonradiative defects on the top surface that were associated with a change in the surface's Fermi level position.

We have studied in situ structures and magnetic properties for several iron silicides grown on Si(111)7×7 clean surfaces by the solid phase epitaxy (SPE) method: deposition of Fe at 40 K and subsequently annealing, and summarized almost all silicide phases depending on the deposition thickness and the annealing temperature as a “schematic magnetic phase diagram”. In the SPE growth, bcc-Fe(111)1×1, c-FeSi(111)1×1, 2×2, and c(4×8), α-FeSi2(112)2×2, ϵ-FeSi(111)√3 × √ 3-R30°, β-FeSi2(101)/(110) and polycrystalline phases are formed on Si(111)7×7 surfaces depending on Fe coverage (0.15–10.0 nm) and annealing temperature (470–1070 K). The structures and magnetic properties of all the above Fe silicide phases have been characterized by using in situ reflection high-energy electron diffraction, scanning tunneling microscopy, and surface magneto-optical Kerr effect. Bulk-unstable c-FeSi phases showed ferromagnetic property at 40 K and this ferromagnetism remained even after air exposure. For the c-FeSi(111)/Si(111) system, the large spin polarization was proposed at the Fe interface atoms in the B5-type interface structure between the c-FeSi(111) ultra-thin film and the Si(111) substrate by first-principle calculations.

Characterizing the angular distributions of photoemission is important for evaluating the elemental composition of materials by hard X-ray photoelectron spectroscopy (HAXPES; HX-PES). These distributions cannot be explained by dipole approximation, and their parameters have been theoretically derived using non-dipole approximation. In this study, the angular distributions of photoelectrons emitted from 3s, 4s, 4p, 4d, and 4f states, observed directly using the HAXPES analyzer with a wide angle objective lens, were investigated by irradiating 8 keV X-rays onto a platinum (Pt) surface. In the 4d and 4f states, the obtained distributions were asymmetric relative to the X-ray polarization vector. This asymmetry was consistent with theoretical results using the non-dipole approximation. Thus, the angular distributions of photoemission predicted by non-dipole approximation were experimentally confirmed at various energy levels of Pt.

To investigate Mg diffusion during ultra-high-pressure annealing, which activates Mg acceptors in GaN, GaN samples with p–n junctions prepared via epitaxial growth were annealed at 1573 K under 1 GPa. The profiles of Mg diffusion toward the underlying n-type layer cannot be explained by a simple diffusion model. We found that H atoms diffused along with Mg atoms. By considering the suppressed diffusion of positively charged interstitial H atoms due to the electric field in the depletion layer, we could better reproduce the Mg–H diffusion profiles, suggesting that H atoms play a key role in the Mg diffusion process.

For accelerating the development of GaN power-switching devices, current knowledge on the origins and dynamic properties of the major intrinsic nonradiative recombination centers (NRCs) in Mg-doped GaN (GaN:Mg) are reviewed, as lightly to heavily doped p-type planar GaN segments are required but certain compensating defects including NRCs hinder their formation. The results of complementary time-resolved photoluminescence and positron annihilation spectroscopy measurements on the epitaxial and ion-implanted GaN:Mg formed on low dislocation density GaN substrates indicate the following: major intrinsic NRCs are the clusters of Ga vacancies (VGas) and N vacancies (VNs), namely VGa(VN)2 in the epitaxial GaN:Mg and (VGa)3(VN)3 in the ion-implanted GaN:Mg after appropriate thermal annealings. The minimum electron capture-cross-sections of VGa(VN)2 and (VGa)3(VN)3 are commonly the middle of 10−13 cm2 at 300 K, which is approximately four times larger than the hole capture-cross-section of the major intrinsic NRCs in n-type GaN, namely VGaVN divacancies, being 7 × 10−14 cm2.

We studied the overall picture of the etching-induced damage for GaN films. By using Ar ion etching, we characterized the damage for GaN from various perspectives by AES, transmission electron microscopy, X-ray absorption spectroscopy, and cathode luminescence. From AES results, it was found that N on GaN surface is selectively etched. After air exposure, the near surface layer within the damage layer was oxidized by the existence of the chemically active dangling bonds. The thickness of the damage layer was observed by cross-sectional transmission electron microscopy as the dimmed layer, which is caused by the absence of translation symmetry, in other words, degradation of the crystallinity introduced by crystal defects and/or transformation into an amorphous phase in nanoscale. Total reflection X-ray absorption near-edge structure spectrum indicated the gradual change from GaN to Ga oxide with higher Ar ion acceleration voltage. Moreover, the etching-induced nonradiative defects were detected by comparing the cathode luminescence intensities. The various phenomena of the damage can be comprehensively evaluated by using these methods, and the overall picture of etching-induced damage for GaN was revealed. Copyright © 2011 John Wiley & Sons, Ltd.

We carried out nondestructive measurements of the depth profile of etching-induced damage in p-type gallium nitride (p-GaN), in particular surface band bending, using Hard X-ray Photoelectron Spectroscopy (HAX-PES). HAX-PES at different take-off angles of photoelectrons made it clear that etching by inductively coupled plasma (ICP) introduced donor-like states in a surface layer of GaN. We were able to quantitatively analyze band bending and charge distribution in an etched p-GaN. The analysis results indicated the existence of deep donors with a concentration of 1―2 x 10 20 cm ―3 in a surface layer whose thickness increased with increasing a bias power of ICP.

Pyramidal inversion domains (PIDs) with (0001) bases several nanometers wide are commonly observed in highly Mg-doped GaN epitaxial layers. High-angle annular dark field scanning transmission electron microscopy clarified the PID boundary structure, concluding debate on previously proposed Mg segregation models: Mg atoms segregate to form a single atomic layer at the boundary and substitute 1/4 of Ga atoms in the neighboring Ga layers. We explain that the Mg segregation produces electrically inactive Mg atoms and can be a cause of the free carrier reduction in the highly Mg-doped GaN. The PID formation process during the epitaxial growth is also discussed.

Photoluminescence (PL) spectra of (000 1 ¯ ) N-polar p-type GaN fabricated by using the sequential ion-implantation of Mg and H with subsequent high temperature annealing exhibited the near-band-edge (NBE) emission at 300 K. The longest PL lifetime ( τ PL ) for the NBE emission of the sample with Mg and H concentrations of 1 × 1019 and 2 × 1020 cm−3, respectively, annealed at 1230 °C was 18 ps at 300 K. This value is almost comparable to that of the (0001) Ga-polar p-type Mg-doped GaN (p-GaN:Mg) homoepitaxial film of the same Mg concentration. By correlating τ PL and the concentration of major vacancy-type defects quantified using positron annihilation spectroscopy, the electron capture-cross-section (σn) of the major nonradiative recombination centers (NRCs), namely, clusters of Ga vacancies (VGas) and N vacancies (VNs) such as (VGa)3(VN)3, is estimated at a few times 10−13 cm2. This σn value is also comparable to that of the major NRCs in p-GaN:Mg epilayers, namely, VGa(VN)2 or VGa(VN)3, although the clustering sizes of the defects are different. These σn values are commonly larger than the hole capture-cross-section (σp = 7 × 10−14 cm2) of the major NRCs, VGaVN divacancies, in n-type GaN.

Stimuli-responsive nanoparticles with fluorescent cross-linked cores were prepared by in-situ Suzuki-coupling reactions of amino acid-based block copolymers using dithiophene- and fluorene-based diboronic acids. Block copolymers synthesized by RAFT polymerization of threonine-containing monomer and 4-bromophenyl vinyl sulfide were used for the self-assembly in a selective solvent and subsequent cross-linking reactions. The formation of stable core cross-linked nanoparticles with stimuli-responsive shell derived from threonine was confirmed by DLS, UV-vis, fluorescence, and CD measurements. Multi stimuli-responsive photophysical properties, depending on pH, salt, urea, and metal species, were evaluated in various organic and aqueous solvents. Figure 1

Extended X-ray absorption fine structure (EXAFS) spectroscopy is demonstrated to measure the fine atomic structure of SiO2–SiC interfaces. The SiC-side of the interface can be measured by fabricating thin SiO2 films and using SiC-selective EXAFS measurements. Fourier transforms of the oscillations of the EXAFS spectra correspond to radial-structure functions and reveal a new peak of the first nearest neighbor of Si for m-face SiC, which does not appear in measurements of the Si-face. This finding suggests that the m-face interface could include a structure with shorter Si–C distances. Numerical calculations provide additional support for this finding.

本研究は，営業列車による軌道モニタリングシステムにおいて位置同定精度を向上し，軌道変状を検出するための手法を開発したものである．はじめに，走行位置同定の高精度化を行った．まず，簡易な GPS (Global Positioning System) 受信機では測位に数メートル以上の誤差があるため，測位点を既存の地図データにおける軌道上の最短地点に配置し，誤差を低減した．また，レール継目の線路キロ程をもとに，位置補正を行った．さらに，同じ区間における計測ケース毎の加速度応答に関して低周波成分の相関を用いて，位置同定精度を向上させた．次に，鉛直成分の加速度応答と軌道変位量との比較により整合性が確認された．また，修繕区間における修繕前後の軌道変化を加速度応答から捉えることができた．

This paper represents a design and development of a mobile sensing unit as well as its prototype implementation for railway track monitoring. The unit consists of an ultra-small personal computer (PC), a global positioning system (GPS) receiver, an accelerometer and an ADC (Analog/Digital Converter) so that the unit can trace the route while capturing an acceleration response of a passenger vehicle. The unit enables more frequent and qualitative data acquisition compared with traditional and the state of the practice railway track inspection equipments. Locating disorder is the key of our unit, which has a reasonable accuracy of positioning with GPS data, existing facilities landmarks, and car acceleration responses. The proposed unit is a promising device for efficient properties management of railway agencies. The prototype implementation shows a result that car acceleration responses are related with the track displacements in low frequencies. The results also imply that sensor settlement on a vehicle floor, not axes or bogies, is effective for capturing track vertical displacements.