Table of contents

Metal halide perovskites can be easily fabricated with low-temperature solution processes, and they are a promising class of materials for solar cells, light emitters, and nonlinear optical devices. The perovskites are direct-gap semiconductors with sharp absorption edges and a highly efficient luminescence with no Stokes shift. In addition, the perovskites exhibit superior optoelectronic properties such as efficient photon recycling and long free-carrier diffusion. In this review, we discuss the fundamental optical properties of bulk crystals and the operation principles of heterodiode devices based on these novel functional materials.

We review the performance of the pyroelectric measurement method in the context of polar states in multiferroic materials in which ferroelectricity coexists with ferromagnetism. The unique point of pyroelectric measurement is the ability to determine the presence of dielectric polarization without having to apply a bias voltage during the measurement. The convenience of the zero-bias technique is illustrated by summarizing experiments on measuring the pyroelectric hysteresis loops of leaky ferroelectric BaTiO₃ and PbTiO₃ thin film capacitors. This technique was also employed for detecting a polar state in magnetic materials, proving that the electronic polarization in ferrimagnetic Fe₃O₄ appears at the Verwey transition temperature at 120 K and to discover A-site-driven ferroelectricity in epitaxially strained ferromagnetic La₂NiMnO₆ films.

Electrically controllable antiferromagnets will play a prominent role in the development of future spintronics. These materials offer a way to realize innovative low-energy-consumption, high-speed, highly integrated spintronic devices for storage, memory, and logic use. The magnetoelectric manipulation of antiferromagnetic spin in Cr₂O₃ is one of the most promising ways to achieve such devices. Crucial problems toward device applications are 1) the establishment of high-quality Cr₂O₃ thin-film fabrication techniques and the demonstration of the adaptability of such films for high-performance devices, and 2) the enhancement of the operating temperature in order to ensure sufficient stability for room-temperature operations. In this review, we summarize the recent progress made in Cr₂O₃ thin-film research, especially focusing on the magnetoelectric manipulation of antiferromagnetic spin and material development for achieving a higher operating temperature in Cr₂O₃ thin films.

Three approaches to obtain flexible ferroelectrics are discussed. The fabrication of freestanding films by etching the substrates allows one to tap on the available perovskite oxide family. Apart from that, van der Waals epitaxy on flexible mica has proved to be a promising technology to create flexible ferroelectrics. Compared with these two methods, the discovery of novel two-dimensional ferroelectric materials eliminates the substrate constraint and extends the candidates of ferroelectric materials for flexible electronics.

The transition metal oxide family harbors various types of materials of interest for spintronics: half-metallic manganites are highly efficient spin injectors and detectors, yielding record values of tunnel magnetoresistance; multiferroic materials, and in particular BiFeO₃, allow the electrical control of magnetization and spin excitations at room temperature; combined with ferromagnets, piezoelectric perovskites enable a controlled tuning of magnetic anisotropy, domain dynamics and even magnetic order. In this review, we argue that a new opportunity is emerging for oxides in spintronics with the rise of spin–orbit-driven phenomena such as the direct and inverse spin Hall and Rashba–Edelstein effects. After surveying the few results reported on inverse spin Hall measurements in oxide materials, we describe in depth the physics of SrTiO₃-based interfaces and their usage for both spin-to-charge and charge-to-spin conversion. Finally, we give perspectives for a more thorough exploration of spin Hall effects in oxides and enhanced conversion ratios in both three- and two-dimensional structures.

The recent resurgence of bismuth ferrite (BiFeO₃) as a multiferroic material was triggered by the revelation of its true bulk physical properties in the mid 2000s. Subsequently, multiferroic properties of BiFeO₃ have been found to improve when it is grown as epitaxial film owing to the biaxial strain imposed by substrate materials. Since the crystal and microstructural modifications caused by the strain dominate the multiferroic property changes in BiFeO₃, tremendous efforts have been devoted to the investigation of structural changes in epitaxial BiFeO₃ films. However, details about strain-induced structural modifications remain elusive owing to the remarkably complex nature of BiFeO₃. In this review, we discuss the followings: (1) what are the pros and cons between transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques, (2) a noble methodology of how to apply TEM and XRD to unambiguously identify crystal symmetries in epitaxial BiFeO₃, and (3) once crystal symmetries are clearly identified, how can the misfit strain be accurately evaluated.

The anomalous Nernst effect (ANE), one of the thermomagnetic effects studied for a long time, is attracting attention again owing to the increased interest in spin caloritronics. Control of the ANE is an essential topic for not only clarifying the interplay among heat, spin, and charge but also application to high-efficiency energy-harvesting devices. In this review, various topics related to the modulation of the ANE are discussed and the possibility of methods for its thermoelectric application are discussed. Systematic studies of the material dependence of the ANE and the discovery of anisotropy in the ANE are reviewed. Enhancement of the ANE in granular thin films and control of the ANE in a ferromagnetic oxide thin film by electric field are also reported. This review provides physical knowledge of the modulation of the ANE and proposes several ways of effectively utilizing the ANE in the "hot" spin caloritronic field.

We demonstrate a significant improvement in the epitaxial growth of perovskite dielectric films on MgO by introducing a SrTiO₃ (STO)/TiO₂ buffer layer, which enhances their dielectric response. 270-nm-thick (001)-epitaxial (Ba,Sr)TiO₃ (BST) films were deposited by pulsed laser deposition on STO/TiO₂-buffered MgO with a SrRuO₃ (SRO) bottom electrode. The film directly deposited on SRO/MgO grew in a three-dimensional mode, resulting in a rough and poorly crystalline film with an almost relaxed strain. On the other hand, the film with a buffer layer grew in a two-dimensional mode, resulting in a flat and highly crystalline film with a large compressive strain (−0.80%). As a result, the paraelectric-to-ferroelectric phase transition temperature increased by 220 °C and an out-of-plane dielectric constant exceeding 1000 was achieved.

The stability of the "T-like" (T') phase in BiFeO₃ films grown on LaAlO₃(001) is investigated. We show that the T' phase can be stabilized for thicknesses >70 nm under ultralow incident flux conditions in pulsed laser ablation growth. This low flux results in a low growth rate; thus, the sample is held at high temperatures (>600 °C) for much longer than is typical. Transmission electron microscopy and X-ray diffraction analysis suggest that such growth conditions favor the formation of nanoscale "defect pockets", which apply a local compressive strain of ∼1.8%. We propose that the cumulative effect of local stresses induced by such "designer defects" maintains macroscale strain coherence mechanical boundary conditions, which then preserves the T' phase to thicknesses beyond conventional wisdom. Finally, by intentionally introducing an amorphous phase at the film-substrate interface, it is shown that the mixed-phase proportion can be tuned for a given thickness.

The magnetic properties of ferromagnetic Ni thin films grown on a Cu(001) single crystal are modified by the growth of a NiO overlayer, as well as by the voltage application through the NiO/Ni interface. A spin reorientation transition from in-plane to perpendicular magnetization is induced with increasing NiO thickness, and the coercive field significantly increases by further growth of the NiO overlayer. The remanent magnetization of the films is found to be modulated by the voltage application. Moreover, a small exchange-bias effect arising from the ferromagnetic–antiferromagnetic interaction at the interface is observed, and the amplitude of the effect is modified by the applied voltage.

We performed time-domain propagating spin-wave spectroscopy for forward spin waves in a ferromagnetic metallic waveguide in the presence of electric current. The forward spin waves exhibit a large propagation delay and a 35% amplitude change with a smaller current injection of 6 × 10¹⁰ A/m², showing a 2 times larger modulation than backward volume spin waves. By measuring electric-current effects in 4 distinct experimental configurations, we found that a current-induced Doppler shift coincided with an Oersted field frequency shift under our experimental conditions. By separating the two phenomena, we evaluated each contribution on the propagating forward spin-wave packet.

Lead (Pb)-free perovskite thin films of the ternary BaTiO₃–Ba(Mg_1/2Ti_1/2)O₃–BiFeO₃ (BT–BMT–BF) solid solution system with preferential crystal orientation were fabricated and the dependence of their polarization behavior on crystal anisotropy was evaluated. The chemical solution deposition (CSD) technique was utilized for the film deposition while controlling the chemical composition. The films fabricated on single-crystal perovskite substrates of (100)SrRuO₃//(100)SrTiO₃ and (111)SrRuO₃//(111)SrTiO₃ exhibited preferential (100)_pc and (111)_pc orientations, respectively, depending on the crystallographic feature on the substrate surface. Excess Bi addition into the precursor solution to compensate for the volatile Bi component enhanced the polarization behavior of the resulting films heat-treated at 750 °C to induce crystallization. The (111)_pc-oriented BT–BMT–BF film had a larger remanent polarization (P_r) of approximately 35 µC/cm² than the (100)_pc-oriented film (P_r = approximately 20 µC/cm²).

The spin Peltier effect (SPE) induced by the spin Hall effect has been investigated in Pt/yttrium-iron-garnet (YIG) junctions by the lock-in thermography technique. First, we propose and demonstrate a new method enabling systematic measurements of the charge-current angle dependence of spin-caloritronic and thermoelectric phenomena, confirming the symmetry of the SPE. Then, to investigate the temporal response of the SPE, we measured the charge-current frequency dependence of the spin-current-induced temperature modulation in a wide frequency range. The SPE signals are found to be almost independent of the frequency up to 100 Hz although the Joule-heating signals in the Pt layer are strongly dependent on the frequency, indicating that the spin-current-induced temperature modulation reaches the steady state in a much shorter time than the conventional heating effects. The experimental methods and results reported here will be useful for clarifying mechanisms and behaviors of spin-caloritronic and thermoelectric phenomena.

(Bi_1−xBa_x)FeO₃ multiferroic thin films with ferromagnetism and ferroelectricity were fabricated by a pulsed DC reactive sputtering and applied to create a magnetic domain using an electric field. The (001)-oriented (Bi_1−xBa_x)FeO₃ thin films, the electric polarization direction of which is perpendicular to the film plane, were fabricated onto a non-single-crystalline substrate with a Ta seedlayer/(111)-oriented Pt underlayer. A low pulse frequency (long time for sputtering OFF) and a high sputtering power (high-energy deposition) were effective for the acceleration of the crystallization of the (Bi_1−xBa_x)FeO₃ phase owing to the enhancement of the surface diffusion of sputtered atoms on the substrate surface. The saturation magnetization of the film was approximately 90 emu/cm³ and the coercivity was approximately 2.5 kOe. Magnetic force microscopy analysis of the (Bi_0.48Ba_0.52)FeO₃ film confirmed that the magnetization was generated by applying only a local electric field. The multiferroic film described here is expected to be useful for electric-field-driven magnetic devices.

The dependence of applied rectangular pulses with various widths on the crystal structure change was investigated by time-resolved synchrotron-based X-ray diffraction measurement. A (001)-oriented epitaxial Pb(Zr_0.5Ti_0.5)O₃ film of 2.1 µm thickness grown on a (100)_cSrRuO₃//(100)LaNiO₃//(100)CaF₂ substrate by metal organic chemical vapor deposition was investigated. The crystal lattice increased almost linearly with increasing applied electric field up to 230 kV/cm in the case of a 0.3-µs-width pulse. This elongation with the application of an electric field was ascertained to be almost independent of the pulse width from 0.3 to 2000 µs at 190 kV/cm. These values were almost consistent with the macroscopic measurements obtained at 5 and 1000 Hz by piezoelectric force macroscopy. The present results show that the time-resolved XRD measurement is very useful for analyzing the frequency dependence of the piezoelectric response in view of the crystal structure change because the crystal structure change under an applied electric field can be systematically investigated by changing the applied pulse width.

The insertion effect of an interface NiO layer on magnetism in Fe/BaTiO₃ is investigated by X-ray absorption spectroscopy (XAS). From X-ray magnetic circular dichroism (XMCD) analysis, the enhancement of remanent magnetization in Fe is observed with increasing NiO thickness. We also find that the NiO layer is partially composed of metallic Ni, and its thickness is estimated to be ∼0.4 nm from the NiO-thickness dependence of the Ni XAS intensity by assuming that Ni is localized at the interface between Fe and NiO. Moreover, extended X-ray absorption fine structure data shows that the Ni–O distance of the interface NiO layer is shorter than that of bulk NiO, which leads to the pseudomorphic growth of NiO on BaTiO₃. We thus suppose that the improved Fe growth promoted by the interface NiO layer enhances the magnetic moment in Fe.

The effects of film thickness and composition on crystal structure and dielectric properties were investigated for {111}-oriented epitaxial Pb(Mg_1/3Nb_2/3)O₃ (PMN) and 0.6Pb(Mg_1/3Nb_2/3)O₃–0.4PbTiO₃ (0.6PMN–0.4PT) films of various thicknesses grown on (111)_cSrRuO₃//(111)SrTiO₃ substrates by pulsed metal organic chemical vapor deposition (MOCVD). When the film thickness of {111}-oriented PMN films increased from 500 to 1300 nm, the relative dielectric constant at room temperature increased from 1600 to 2800 at 10 kHz. This tendency was similar to our previous result for {100}-oriented PMN films. On the other hand, the relative dielectric constant at room temperature slightly increased from 2500 to 2700 at 10 kHz with the increase in film thickness from 750 to 2500 nm in the case of {111}-oriented 0.6PMN–0.4PT films. PMN films show strong frequency dependences of maximum relative dielectric constant against temperature, ε_r(max), and the temperature of ε_r(max), T(max), together with a strong thickness dependence. On the other hand, 0.6PMN–0.4PT films show small frequency dependences of ε_r(max) and T(max) together with a small film thickness dependence. These results show a strong film composition dependence of the dielectric properties of the films in a PMN–PT system such as frequency and thickness.

We demonstrated the grain size effect on piezoelectric properties of pure BaTiO₃ ceramics. BaTiO₃ ceramics with various grain sizes were prepared by conventional and two-step sintering methods. The piezoelectric strain constant d₃₃ increased with decreasing grain size when the grain size was more than 1.2 µm, whereas it decreased when the grain size was below 1.2 µm. The maximum d₃₃ was 460 pC/N, which is approximately three times larger than that of coarse BaTiO₃ ceramics. The increase in d₃₃ was well explained by the domain-wall contribution, while the decrease in d₃₃ was understood as the grain boundary effect. On the other hand, the piezoelectric voltage constant g₃₃ increased with decreasing grain size down to 0.6 µm. The piezoelectric constants d₃₃ and g₃₃, and the mechanical quality factor Q_m can be controlled by the grain size of BaTiO₃ ceramics.

The crystal structure of bismuth ferrite (BiFeO₃; BFO) epitaxial films was analyzed by X-ray diffraction (XRD) using a two-dimensional detector. The diffraction spots $(2\bar{1}\bar{3})$_hex (hexagonal notation was used for the rhombohedral structure in this study) specific to the rhombohedral structure (space group: R3c), which clearly separated from the diffractions in other crystal symmetries of BFO, was used for determining the crystal symmetry. The BFO films on the SrTiO₃ substrates were unambiguously identified as R3c with the $(2\bar{1}\bar{3})$_hex diffraction spot, whereas highly strained BFO films (space group: Cm) on the LaAlO₃ substrates did not show the diffraction spot. The structure of a single-domain-like sample with R3c could not be determined using variants, i.e., degrees of freedom for crystal orientation, whereas the Bragg's diffraction of $(2\bar{1}\bar{3})$_hex can be used to unambiguously distinguish R3c from other space groups. It was proposed that electron diffraction complemented by nondestructive and high-resolution XRD is highly effective to obtain wide-area reciprocal space information for identifying low-symmetric-complex materials such as BFO.

Local magnetic structures of spinel-type FeV₂O₄ were investigated using X-ray absorption and X-ray magnetic circular dichroism (XMCD) spectroscopies for V and Fe sites and Mössbauer spectroscopy for Fe sites. XMCD spectra reveal that the Fe²⁺ (d⁶) and V³⁺ (d²) states are coupled antiferromagnetically. From the analyses of XMCD spectra using magneto-optical sum rules, we deduced that small but finite orbital magnetic moments remain in the V 3d states, which accounts for the ferro-orbital ordering in the V sites of FeV₂O₄ with both the complex and real orbital states coexisting accompanied by the distortion of Fe sites. X-ray absorption fine structure spectra supports the deduction that the Fe²⁺ and V³⁺ states remain unchanged during the structural phase transitions. Mössbauer spectra also suggest that the Jahn–Teller distortion in Fe sites can be a driving force in ferro-orbital ordering.

A spin metal–oxide–semiconductor field-effect transistor (MOSFET) is a promising spintronics device for future low-power electronics. In this paper, we demonstrate the successful improvement of the performance of a spin-MOSFET-type device, a ferromagnetic-semiconductor GaMnAs-based vertical spin electric double-layer transistor (EDLT); the magnetoresistance ratio reaches 37%, which is 7 times larger than those obtained in previous studies. Furthermore, we find that the magnetic anisotropy of our device is modulated by changing the gate voltage. Our results open up the possibility of realizing novel functional devices, in which both current and magnetic anisotropy can be controlled by the gate electric field.

We measure polarized photoluminescence emitted from excitons bound to the 1.508 eV N–N impurity pairs in the ultra-dilute semiconductor alloy GaAs:N grown by both metalorganic chemical vapor deposition (MOCVD) and MBE. In MOCVD-grown GaAs:N, the pair orientation is random, with pairs equally distributed over the two equivalent directions in the growth plane. In contrast, MBE results in a highly uniform ensemble of in-plane pairs preferentially aligned in a single 〈110〉 direction, and the population of out-of-plane pairs reduced. The results are important for quantum control of N pair qubits where observable energy levels depend on pair orientation.

The creation of atomically-ordered Si{111}7 × 7 facet structures on a Si(110) substrate is realized for the first time. Au was deposited on atomically-flat {111} facet surfaces. The resistance of Au wires crossing over three-dimensional (3D) facet edges with an angular shape is intrinsically sensitive to the edge alignments in electric path: the resistance in crossing the facet edges was 3–10 times larger than that along the facet edges. We suggest the enlargement of the resistance originated from conduction electron scattering along the angular path. This work pioneers the fundamental understanding of electron transport in 3D angular metal-interconnects.

We propose a multi-band infrared coherent perfect absorber where four perfect absorption peaks can be obtained for antisymmetrical inputs. The FWHM is nearly four times larger than that of a single band absorber. In addition, the absorptivity of each peak can be independently tuned by phase modulation. Since only magnetic resonances in the form of catenary optical fields in the upper and lower dielectric layers can be excited for symmetrical inputs, the number of absorption peaks will be reduced by half at this time. The absorption frequency under symmetrical inputs can be flexibly selected from low frequency to high frequency by changing the material of the upper and lower dielectric layers. Moreover, the bandwidth in optimized broadband absorber is enhanced by 9 times while high absorbance is maintained. The characteristic of the enhancing absorption bandwidth and the selective absorption may allow our metasurface to be used in many applications such as optical switch and modulators.

We demonstrate optically-pumped waveguides grown on freestanding GaN substrate featuring AlInN claddings and GaN/Al_0.1Ga_0.9N multiple quantum wells exhibiting narrow bandwidth (3.8 nm) optical gain around 370 nm. Due to the high refractive index contrast between the cladding layers and the active region, the confinement factor is as high as 48% and net modal gain values in excess of 80 cm⁻¹ are measured. The results agree well with self-consistent calculations accounting for built-in electric field effects and high carrier density related phenomena. These results open interesting perspectives for the realization of more efficient near-UV lasers and optical amplifiers.

This paper reports photosensitive organic–inorganic hybrid polysiloxane (Poly-SX) based passivation fabricated at low temperatures under 180 °C for high performance and highly reliable amorphous InGaZnO (a-IGZO) TFT. The Poly-SX passivation can be fabricated by solution and photolithography process without needing any dry etching process. The passivated a-IGZO TFT has a high field effect mobility reaching 10.91 cm² V⁻¹ s⁻¹ and enhanced reliability with a threshold voltage shift as low as +2.0 and −0.9 V after positive (PBS) and negative bias stress (NBS), respectively. These results demonstrate the possibility of fabricating passivated a-IGZO TFT on various flexible organic substrates at low temperatures by solution process.

The ultrafast demagnetization of metallic ferromagnets can generate a spin current in metallic nonmagnets in a ferromagnet/nonmagnet structure. Two different mechanisms for this phenomenon have been suggested: spin-dependent transport of hot electrons and spin generation by electron–magnon scattering. In this work, we optically measure a transient spin accumulation on a nonmagnetic Cu layer driven by the ultrafast demagnetization of a ferromagnet (Fe, Co, and Ni). The modeling based on the spin generation by electron–magnon scattering in bulk ferromagnets (namely, bulk spin pumping) well explains the dynamics and magnitude of the measured spin accumulation on Cu.

A simple dual-interference-channel quantitative phase microscope is demonstrated by using a cube beamsplitter and a Fresnel biprism. The beam is incident to only one-half of a tilted cube beamsplitter and then two copies of the incident beam are generated. One Fresnel biprism is used to deflect these two copy beams toward each other and then form an interference pattern. The sample is adjusted to only interact with one-half of the incident beam, and then two interference channels with a relative π (rad) phase shift in one interferogram can be observed simultaneously. A quantitative phase image of a biological cell is obtained successfully.

We demonstrate wash-free detection of C-reactive proteins (CRPs) based on third-harmonic signal measurement of magnetic markers. In the method presented here, the CRP concentration can be detected from the decrease in the third-harmonic signal from the sample solution. The relationship between the detected signal and the CRP concentration can be modeled quantitatively using a logistic function. The quantities of CRP that were detected using the proposed method showed good correlation with those obtained using the conventional optical method with a washing process. We also demonstrate CRP detection in a hemolysis sample solution that is not optically transparent.

The Rydberg atom can be used as an active probe for precision radio-frequency (RF) electric field (E-field) measurement; however, the RF cavity resonance and scattering effect of an atomic vapor cell lead to polarization distortion inside the cell, and the depolarization effect limits the sensitivity and accuracy of E-field measurement. The finite element simulation and characteristic mode analysis of a hollow-cavity model are implemented to find an optimized solution of minimizing such depolarization. Manipulating atoms in the middle layer of a vapor cell along an incident field vector can avoid the depolarization, which is validated by the vector distribution measurement at 15.09 GHz.

An ultra-wideband reflective polarization conversion metasurface (PCM) is designed, which has a periodic multi-V-shaped subwavelength structure printed on a metallic plate backed with a dielectric substrate. Four resonances are generated under the normal incidence of plane waves, which leads to bandwidth expansion of the cross-polarization reflection. The proposed PCM can efficiently convert linear polarized waves to their orthogonal polarization counterpart in an ultra-wideband ranging from 14.3 to 43.2 GHz efficiently with an average polarization conversion ratio (PCR) of 96.7%.

In this work, we investigated individual Co nanosheets by dynamic cantilever magnetometry. For a disk sample, fitting results give consistent magnetic anisotropy from in-plane and out-of-plane magnetization processes. The derived saturation magnetization value is comparable to the bulk value. However, for a rectangular sample, there is a considerable difference between the derived anisotropy constants from the in-plane and out-of-plane. Moreover, the derived saturation magnetization value is much smaller than the bulk value. We conclude that for samples without rotation symmetry, the uniaxial anisotropy assumption is not applicable and a biaxial or more complex magnetic anisotropy should be taken into account in analyzing dynamic cantilever magnetometry measurements.

We investigate the effects of atomic layer deposition (ALD)-grown Al₂O₃ buffer layer on the device characteristics of flexible amorphous InGaZnO thin-film transistors (TFTs) fabricated on ultrathin polyimide (PI) films. The TFT with a buffer layer exhibited a saturation mobility of 8.6 cm² V⁻¹ s⁻¹ and a subthreshold swing of 0.16 V dec⁻¹ after annealing at 150 °C. Under negative bias temperature stress at 40 °C, the turn-on voltage instabilities of TFTs with and without the buffer layer were estimated to be −1.0 and −13.2 V, respectively. This marked difference is mainly due to the adsorption of water molecules on the PI film resulting in a positively charged surface.

Multiple-beam diffraction X-ray topography was used to determine the Burgers vector b of threading edge dislocations (TEDs) and basal plane dislocations (BPDs) in 4H-SiC epitaxial layers. In hexagonal crystals, the technique simultaneously yields five different diffractions corresponding to different diffraction vectors g. Hence, this method enables us to determine the components of b using the g · b = 0 rule without widely changing the diffraction geometry. The b vectors of TEDs and BPDs were successfully determined by the method. These results were then confirmed by ordinary grazing-incidence X-ray topography in order to verify the validity of this technique.

The behavior of a cholesteric liquid crystal (CLC) cell under the voltage application condition was quantitatively investigated. To observe the realignment of the CLC including helical pitch and tilt angle changes, the phase delay change and amplitude reduction of transmitted light were measured simultaneously and individually using a Mach–Zehnder interferometer. Compared to a numerical simulation based on a 4 × 4 method, changes in the helical pitch and tilt angle of the CLC cell were quantitatively determined.

The significance of metastable acceptors in Cu(In,Ga)Se₂ (CIGS) solar cells in accelerated lifetime testing has been investigated. Dry heating under light irradiation improves the conversion efficiency of CIGS solar cells at the early stage, which slightly decreases after long-term testing. However, after dry heating in the dark, the conversion efficiency significantly decreases. The net acceptor concentration considerably decreases after dark heating, and the reduction in the number of metastable acceptors results in decreases in open-circuit voltage and fill factor. After heat illumination treatment, the net acceptor concentration increases because of the metastable acceptors in CIGS layers, and the open-circuit voltage and fill factor partly recover. Therefore, the concentrations of metastable acceptors should be controlled by light irradiation or current injection with positive bias to evaluate correctly the degradation rates during accelerated lifetime testing.

Nonradiative recombination (NRR) centers in as-grown and proton-irradiated InAs/GaAs quantum dot (QD) structures have been studied by two-wavelength-excited photoluminescence (PL). The PL intensity quenching of GaAs and QD emissions due to the addition of a below-gap excitation light of 0.80 eV energy indicates the presence of defect levels acting as NRR centers. The method enables us to discuss the distribution of NRR centers in GaAs and/or InAs QD regions by selecting either conduction band excitation (2.33 eV) or intermediate band excitation (1.27 eV). We have found that the densities of NRR centers in GaAs layers and the effect of quenching on GaAs emissions increase monotonically with increasing proton irradiation fluence. The QD emission intensity, however, increases at a moderate fluence of 7 × 10¹¹ protons/cm² owing to the defect-assisted trapping of electrons into QDs. Further incorporation of NRR centers after 4 × 10¹² protons/cm² fluence quenches the QD-PL intensity below that of an unirradiated sample.

A highly sensitive refractive index (RI) sensors based on a fiber in-line Mach–Zehnder interferometer (MZI) with a multimode fiber–thin core fiber–multimode fiber (MMF–TCF–MMF) structure was proposed and demonstrated. This MZI has shown a good interference visibility as high as 16 dB in air. Experimentally, the sensor exhibited high RI sensitivity, with a max sensitivity of up to 453.99 nm/RIU in the RI range of 1.3330–1.3904. Furthermore, the dependences of RI sensitivity and TCF length were also analyzed. In addition, the proposed sensor has the advantages of simplicity of fabrication, low cost, compact size, and high sensitivity, which are beyond what conventional RI sensors can offer.

A computationally efficient numerical simulation of a diode-pumped alkali laser (DPAL) has been developed. It considers the thermal lensing effect by a wave-optics optical resonator model coupled with a simplified gas-flow model. The calculation results indicate that the proposed gas-flow model correctly predicts the temperature distribution of the active medium heated by exothermic reactions. As a result, there is good agreement between the calculations and experiments, especially with the output power as a function of the gas-flow velocity. The calculations have shown that the population of the high-lying excited levels of the Cs atom is negligible within a pump power intensity of 10 kW/cm².

Magnetic and fluorescence properties of chemically synthesized Yb_0.45Gd_2.55Sc₂Al_3−xFe_xO₁₂ (Yb:GSAIG) nanocrystals have been investigated as a function of Fe³⁺ composition x. Structural characterization of the samples by X-ray diffractometry (XRD) has shown that they are in a garnet phase when 0 ≤ x ≤ 2.5. According to XRD Rietveld analyses, Sc³⁺ selectively occupy the octahedral (16a) sites, while Al³⁺ and Fe³⁺ go to the tetrahedral (24d) sites in the garnet. The Fe³⁺ occupancy at the 24d sites increases with increasing x. The intensity of Yb³⁺ fluorescence observed at emission wavelength ∼1030 nm decreases with increasing x from 0 to 2.5. The absorbance due to Fe³⁺ at the 24d sites increases with increasing x, indicating that the fluorescence sensitively varies with x. All the samples exhibit a paramagnetic behavior at low temperatures 5–300 K. Their magnetization at 5 K decreases with increasing x under magnetic fields up to ±40 kOe.

We report the degrees of biaxial orientation for (Y_1−xEr_x)Ba₂Cu₃O_y [(Y_1−xEr_x)123] powder samples aligned in epoxy resin under a modulated rotating magnetic field of 10 T at room temperature. Although the triaxial magnetic anisotropy of ErBa₂Cu₃O_y was found to be approximately 20 times higher than that of YBa₂Cu₃O_y, the orientation degrees for (Y_1−xEr_x)123 powder samples decreased with x. In the fabrication of (Y_1−xEr_x)123 powders, sintering temperature is one of the parameters that predominantly affect orientation degree, and the sintering at temperatures close to the peritectic temperature leads to improvement of the orientation degree. In the case of the biaxial magnetic alignment of REBa₂Cu₃O_y (RE123: RE, rare-earth element) powders, the reduction of in-plane magnetic anisotropy induced by twin microstructures at the RE123 grain level should be taken into account. Therefore, in this study, we clarified that the fabrication processes of RE123 powders are important in addition to the control of the chemical composition using RE ions with high magnetic anisotropy.

An optical mode converter between hybrid device and Si waveguide is the key component for efficient and stable operation of III–V/silicon-on-insulator (SOI) hybrid photonic integrated circuits (PICs). In this study, we introduced a double taper structure into such a mode converter and investigated the coupling efficiency dependence on their structural parameters. By using N₂ plasma activated bonding technology, III–V/SOI double-taper-type mode couplers with various taper-tip-widths and taper lengths were fabricated, and their coupling efficiencies were evaluated. As the result, a coupling efficiency of as high as −0.2 dB was achieved for a double-taper device with a tip width of 0.4 µm and total length of 85 µm.

In this paper, a high-k stacked and SiO₂ gate structure is proposed for the fully depleted silicon-on-insulator (FDSOI) MOSFET. We constructed a two-dimensional (2D) model to compute its subthreshold surface potential, threshold voltage, drain-induced barrier lowering (DIBL) effect and fringing-induced barrier lowering (FIBL) effect. Given the structure and wide range of dielectric permittivities of a FDSOI MOSFET, the device in the subthreshold mode is separated into four distinct rectangular equivalent sources, 2D boundary value problems of the Poisson and Laplace equation are built on the polygon region. We used the eigenfunction expansion to solve the 2D boundary value problems and obtain their semianalytical solutions. The computational outcomes demonstrate that the high-k and SiO₂ stacked gate structure can suppress the degradation of the FDSOI MOSFET threshold voltage and the aggravation of the DIBL effect. The computational cost of this model is much lesser than traditional models; thus, it can be used for circuit simulators and modeling of FDSOI MOSFETs.

Using a multi-diamond-wire saw, we cut monocrystalline silicon bricks into thin (120 µm) wafers, on which we observed saw marks and elongated pits with surface cracks. To address the fracture issues, we performed three-line bending tests with the load applied in the parallel and perpendicular direction to the saw mark direction. Under parallel loading, pits and accompanying cracks resulted in lower fracture strength than under perpendicular loading and the wafers were clearly separated into two groups: lower-strength wafers from the fresh-wire side and higher-strength wafers from the worn-wire side. Under perpendicular loading, the pits and surface cracks had less effect, resulting in higher strength. Using Raman spectroscopy, we confirmed that the wafers from the fresh-wire side had a higher fraction of slicing damage on the surface and subsurface region than those from the worn-wire side. This damage resulted in lower-strength wafers in the parallel loading test.

Since the actual and microscopic structure of hard-sphere-type colloidal crystals has not been fully understood, we performed detailed microscopic structural characterization of the sedimentation-grown opal-type colloidal crystals by conventional optical microscopy, laser conforcal microscopy, and secondary electron microscopy. It is directly proved for the first time, to the best of our knowledge, that iridescent striations originate from the repetition of twin structures and stacking faults in crystal structures. We propose "subdomain" as an intrinsic constitutional unit of a monocolored iridescent "domain" and the subdomain boundary is defined as the envelope of the edges of stacking faults. Every domain forming the bulk crystal contains a high concentration of slanted stacking faults at various tilt angles inherent to the domain. These observations show that the bulk colloidal crystals can be described in terms of five stages of hierarchical structure units, bulk crystal, domains, sub-domains, pristine single-crystal lamellae, and silica particles.

Solid phase epitaxial (SPE) recrystallization of amorphous Si on a Si(001) substrate was examined by large-scale (6144–129024 Si atoms), long-time (up to 2000 ns) molecular-dynamics (MD) simulations using the empirical Tersoff interatomic potential. We particularly focused on the effects of the MD cell size, simulation time, and ensemble on the SPE growth rate. We found that the simulations under the isothermal–isochoric conditions (NVT ensemble) show a higher crystallization rate than those under the isothermal–isobaric conditions (NPT ensemble). The system size dealt with in the present MD simulation, i.e., >6144 Si atoms, was enough to estimate the SPE growth rate. The Arrhenius plot of the growth rate between 1300 and 1600 K exhibited a single activation energy, ∼2.4 eV, which is in agreement with the experimental value (∼2.7 eV). However, the growth rate at temperatures below 1300 K deviated from the extrapolated ones from 1300 to 1600 K, which is because recrystallization does not reach a steady state: long-time MD simulations are required to estimate the growth rate at low temperature. The structure analysis of amorphous/crystalline interfaces suggested that the braking of atomic bonds parallel to the interface becomes a rate-limiting step of the SPE growth.

The carbonation behavior and decarbonation annealing of a protective (Mg,Ca)O layer for flat panel plasma discharge devices were investigated. Compared with a conventional MgO protective layer, the (Mg,Ca)O protective layer showed both high and low discharge voltages. Quantitative X-ray photoelectron spectroscopy analyses indicated that the high discharge voltages were caused by Ca carbonation. The progression of Ca carbonation was enhanced by exposure to air containing H₂O but not by exposure to dry air. In addition, once (Mg,Ca)O is carbonated, it is impossible to decarbonate Ca by annealing in air at the temperature applied during the production process. We propose the use of annealing in vacuum as an effective method to promote the decarbonation of Ca and maintain a low discharge voltage for plasma discharge devices with (Mg,Ca)O protective layers.

The breakdown in air and SF₆ caused by a high power microwave pulse is investigated using a global model, respectively, in which the rate coefficients such as an ionization rate derived from the Boltzmann equation solver BOLSIG+ are adopted. The breakdown prediction from the global model agrees very well with experimental data. The relation curves among the effective breakdown threshold, pressure, and total duration of pulse with either different frequencies or different duration of pulse are nearly the same, but change with the background gas species. At atmospheric pressure, the breakdown threshold of SF₆ for a long microwave pulse is about three times larger than that of air. However, the ratio decreases, when the gas pressure or the total duration of pulse is decreased.

The ignition probability of a premixed burner flame was improved in the effluent of a dielectric barrier discharge. In addition, the propagation speed of the flame kernel was increased by the dielectric barrier discharge. The increase in the propagation speed of the flame kernel was more significant in the region close to the nozzle of the effluent gas. We measured the spatial distributions of the densities of OH and atomic oxygen in the effluent. We found that the axial decay of the density of atomic oxygen was steeper than that of the OH density under the experimental conditions. By comparing the spatial distributions of the radical densities with that of the propagation speed of the flame kernel, we concluded that atomic oxygen works more effectively than OH in improving the ignition probability of the premixed burner flame.

Plasma application for environmental pollution control is desirable, and it is important to clarify the chemical reaction processes in nonthermal plasma. In this study, the discharge polarity dependence of the density and rotational temperature of OH radicals is measured by laser-induced fluorescence (LIF) in coaxial-cylinder pulsed dielectric barrier discharge (DBD) in atmospheric pressure humid air. The density of OH radicals generated by a pulsed positive DBD of +28 kV is estimated to be in the range of 6–10 × 10¹⁴ cm⁻³ at 3 µs after discharge near the central electrode. The rotational temperature rises after the discharge and the rate of temperature rise increases with humidity. In negative discharge, the decay rate of OH density, which directly depends on the initial OH density, is lower than that in positive discharge. The OH amounts contained in the observed area are almost the same in positive and negative discharges. These results indicate that the negative streamer diameter is twice the positive streamer diameter and the OH density in negative DBD is a quarter of that in positive discharge. In the chemical treatments using OH radicals, negative streamer DBD is supposed to be superior to positive streamer DBD from the perspective of ineffective loss. The temperature behavior in negative discharge is similar to that in positive discharge.

We describe the effects of the plasma-activation of a medium on the killing of cancer cells, in which the plasma-activated medium is produced by the irradiation of the cell culture medium using a low-frequency (LF) or very-high-frequency (VHF) plasma jet. The plasma-activated medium produced by the direct contact of the LF plasma jet with the liquid surface induces much lower cancer cell viability, and large amounts of oxidation products, such as gluconic acid and methionine sulfoxide, can be detected in the plasma-activated medium. Our experiments show that the process of using plasma created by the direct contact of a LF plasma jet leads to a plasma-activated medium with stronger cancer-cell killing ability compared with a no-contact process. Also, the oxidation products, such as methionine sulfoxide in the plasma-activated medium become useful proxies for lethality.

To reduce design pressure for the upstream DC gun, this paper proposes a challenging task of improving bunching capacity for an independent tunable cavity (ITC) RF gun employed in a high power terahertz (THz) free electron laser (FEL). Based on a one-dimensional model for various ITCs, comparisons of their bunching capacities are conducted according to motion and momentum trajectories of the electrons passing through. Since the bunching performance is determined by longitudinal properties of the first cell, special axial electrical fields are designed for it. Furthermore, in the process of structure design, besides inheriting merits of the original configuration, a new idea called "duty sharing" — each part is in charge of a different function for designing such a gun — is applied. Additionally, physical design for the new configuration shows that the proposed task can be accomplished, while the FEL gain length is almost the same as in the previous design.

We investigated the reaction process in magnetite nanoparticle (MNP) synthesis by glow-discharge electrolysis in atmospheric air combined with iron electrolysis using NaCl aqueous solution as electrolyte. The iron electrolysis supplies Fe²⁺ in the solution, and electrons from the glow discharge induce liquid-phase reactions. We found experimentally that the concentration of dissolved oxygen (DO) in the solution is a key parameter in MNP synthesis. The excess oxidation of ferrous iron species at a high DO concentration causes the generation of hematite nanoparticles, while MNPs are mainly synthesized at a low DO concentration. Simple rate equations were solved to investigate the liquid-phase reaction process. The calculated results showed that the DO concentration reasonably changed the ratio between ferrous and ferric iron species, which will be important for the chemical composition of synthesized nanoparticles. The solution pH, which is locally increased by the glow discharge, affects the liquid-phase reaction process, especially through the hydroxylation of ferrous iron species.

In this paper, a detailed fluid model is developed for the conversion of methane to methanol with hydrogen peroxide vapor in an atmospheric dielectric barrier discharge. The two-dimensional axisymmetric fluid model is constructed, in which 107 plasma chemical reactions and 28 different species are considered. Our attention is focused on physicochemical mechanism of methanol formation during the complicated chemical reaction processes of reactant molecules dissociation by electron impacting and neutral radical recombination. First, spatial and temporal characteristics of main radicals and ions, such as H, CH₃, OH, CH₃OH, CH₃O, CH₂OH, CH₄⁺, CH₃⁺, H₂O₂⁺, and H₂O⁺, are presented. It is found that the streamer discharge is sustained by the direct electron-impact ionization of methane molecules. The dominant positive ion flux on to the dielectric surface is methane ion, and its peak value is located at axis. Then, the dominant chemical routes governing the production and loss of CH₃OH and OH are discussed in detail. Finally, a schematic overview of dominant plasma reaction pathways for partial oxidation of methane to methanol with hydrogen peroxide vapor in atmospheric dielectric barrier discharge is summarized.

Photoresists are an indispensable technology used for manufacturing electronic devices such as displays and semiconductors. In this study, we investigated the relationship between C=C double bond conversion and dissolution kinetics in cross-linking-type photoresists used for display manufacture using real-time Fourier transform infrared spectroscopy (FTIR) and quartz crystal microbalance (QCM) methods. To improve photoresist performance, it is important to understand the development mechanism of photoresists. Two kinds of polymers (a polymer with peeling-type dissolution and a polymer with a dissolution type with Case II diffusion) were used. 1,2-Octanedione-1-[4-(phenylthio)-2-(O-benzoyloxime)] and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide were used as photoinitiators. The dissolution was of the peeling type when the polymers were formulated as a typical cross-linking-type photoresist. With increasing conversion ratio of C=C double bonds, the rate of developer intake decreased and the impregnation threshold before the onset of peeling increased and then decreased. It was also found that the dissolution kinetics were affected by the radicals generated upon the decomposition of photoinitiators.

In this paper, a novel gate dielectric and passivation technique for GaN-on-Si AlN/GaN metal–insulator–semiconductor high-electron-mobility transistor (MIS-HEMT) is proposed. This technique features the AlN thin film grown by thermal atomic layer deposition (ALD) at 360 °C without plasma enhancement. A 10 nm AlN thin film serving as gate dielectric and passivation layer in the access region was grown. Compared with the Schottky gate AlN/GaN HEMT (SG-HEMT), the fabricated thermal ALD-grown AlN MIS-HEMT exhibits enhanced I_on/I_off ratio, reduction of gate leakage by 5 orders of magnitude at a bias of 5 V, and suppressed current collapse degradation.

We investigated the fundamental characteristics of a CH₃O-ion-implanted silicon epitaxial wafer with our previously developed multielement molecular ion implantation technique and compared this technique with a conventional implantation technique, i.e., "carbon cluster ion implantation". We found that the CH₃O ion projection range has a 10-fold higher oxygen concentration than the carbon cluster ion projection range after epitaxial growth. We also found 50 nm silicon {111} stacking faults in the CH₃O ion projection range. Such defects were not observed in the carbon cluster ion projection range. From nickel gettering test results, proximity gettering of nickel contaminations by CH₃O ion implantation was found to be more effective than that by C₂H₃ ion implantation. Therefore, we speculate that the CH₃O ion projection range improves the gettering capability of metallic impurity contaminants through the formation of complex point defects formed by vacancies and that oxygen implanted at a high concentration and silicon {111} stacking faults are new gettering sinks.

We propose a new approach to generating unidirectional transmission of acoustic waves using transmitted and reflected acoustic metasurfaces (AMSs). Our research is supported by both theoretical arguments and simulations. Such an approach can realize unidirectional acoustic transmission in a certain frequency band. Transmission efficiency is maintained high owing to the impedance-matching condition while allowing other objects, both fluid and solid, to pass freely through the acoustic channel. The simulation results are in accordance with the theoretical predictions. Moreover, because of the simple geometric profile of these AMSs, the approach should be useful and easy to implement as an integral part of more complex technologies related to medical ultrasound and noise insulation.

The stability of group-III nitrides on a N-polar AlN substrate with Al overlayers is theoretically investigated using an ab initio approach that yields the energy for individual polar interfaces. We find that the trends in the interface energy depend on the number of Al overlayers m. The interface energies of Al- (Ga-) polar AlN (GaN) with m = 2 and 4 are lower than those of N-polar AlN (GaN). The calculated results suggest that the formation of stable bonds between the topmost layer of Al overlayers and the bottom layer of group-III nitrides is crucial for the polarity inversion on a N-polar AlN substrate.

A simple monitoring method for micro-arc discharge in plasma etching process has been developed. This method employs a current transformer, a Rogowski coil, which is externally attached to encircle a ground lead of a process chamber in plasma etching equipment without touching the lead. The results in this study demonstrate that this method can monitor the current flowing to ground, which reflects load current, and can detect micro-arc discharge occurring in plasma etching process. This easy-to-use, noncontact, and inexpensive method can contribute to improving the overall equipment effectiveness and the production yield in the wafer process in the mass production of LSI.

We investigated native oxides on GaN(0001) using high-resolution scanning transmission electron microscopy (STEM) and ultraviolet photoemission spectroscopy (UPS). As a result, it was confirmed that the native oxides on both n-type and p-type GaN(0001) with a thickness of ∼1 nm were not amorphous but crystalline with lattice-matched structures to GaN, as we reported previously [Y. Irokawa et al., Jpn J. Appl. Phys. 56, 128004 (2017)]. Moreover, the UPS spectra of native oxides on n-type GaN(0001), which were similar to the reported clean GaN(0001) spectra, showed the existence of surface states at the valence band maximum (VBM), reflecting the defective quality of the native oxides.

A Si deep-trench etching process using HBr/SF₆/O₂ plasma was studied. It was found that when the hole trench width was decreased from 190 to 140 nm, erosions at the topmost part of the Si hole sidewall were observed at an incidence of 10 ppm, which was checked from top-down views of 928 million hole shapes per wafer. It was confirmed that when the cathode temperature was increased to 140 °C, no Si erosion occurred. It was found that etching at a higher temperature reduced the halogen content in the film deposited on the sidewall, making the film more protective, and suppressed Si erosion.

The fabrication and filling of carbon nanomaterials (CNMs) into nanoholes and trenches using supercritical method were achieved for the first time at substrate temperatures of 500–700 °C and pressures of 10–20 MPa. Two supercritical fluid systems were examined: (1) ethanol and carbon dioxide were used as the carbon source and supercritical fluid, respectively, and (2) ethanol was used as both the carbon source and supercritical fluid. Multiwalled carbon nanotubes with diameters of 8–20 nm were also confirmed to be formed. The present work introduces a new technique of preparing CNMs for application as large-scale integration interconnects.

We present percolative arrays of gold nanoparticles (NPs) formed in a resist groove. To enhance the connection probability, the width of the resist groove (140 nm) was designed to be approximately five times larger than the diameter of gold NPs (30 nm). Two-stage deposition of gold NPs was employed to form bridge connections between the source and drain electrodes. Dithiol molecules coated on surfaces of gold NPs worked as tunnel barriers. 5 of 12 samples exhibited Coulomb blockade characteristics, in one of which the gate response was confirmed.

In this study, we investigate how the duration of trimethylaluminum (TMAl) flow steps used before aluminum nitride (AlN) growth affects the crystal quality of an AlN layer and, in turn, the surface morphologies of a gallium nitride (GaN) layer in a GaN-on-AlN-on-silicon (111) structure. A high pit density was observed on a GaN surface grown under an incorrect pre-AlN-growth TMAl step duration. Transmission electron microscopy revealed that crystallographically inclined AlN crystals were contained in the AlN layer grown after the duration, and that these crystals impeded the GaN layer from growing. When the pre-AlN-growth TMAl step duration was short, a high density of dislocations was generated in the AlN layer, and polycrystalline growth began on the AlN surface. When the duration was long, an excessive amount of aluminum reacted with silicon, forming a silicon-aluminum alloy, and the AlN layer grown on this alloy contained crystallographically inclined crystals.

We use steady-state capacitance measurement originally intended for capacitance–voltage experiment to observe and characterize the electrical properties of deep defects in β-Ga₂O₃ semiconductors. We detect a deep level located 0.81 eV below the conduction band edge with a concentration of 1.2 × 10¹⁶ cm⁻³ and a capture cross-section of 1.1 × 10⁻¹⁴ cm², making it potentially influential in determining the performance of β-Ga₂O₃ based power electronic and optoelectronic devices. This deep level may dominate the thermal activation of off-state drain current in β-Ga₂O₃ transistors at high temperatures and, together with another shallower level at 0.13 eV, may substantially lower the breakdown voltage in Schottky diodes.

The ion beam induced formation of nanoporous structures on the surface of Ge under controlled conditions of ion dose, flux, and irradiation angle using a focused ion beam was investigated by electron microscopy. The formation of large-scale nanoporous structures on the surface of the Ge specimens with increasing ion dose and increasing flux was observed via nanostructural characterization using scanning electron microscopy and transmission electron microscopy (TEM). Compared with the structure formed under irradiation at 0°, that formed under irradiation at 45° was tilted and large-scale. These results suggest that the number of point defects per unit volume of surface is important for the formation of a nanoporous structure. TEM observations revealed that the nanoporous structural features formed during the initial process were not voids but surface roughness. This mechanism differs from the nanoporous structure formation mechanism of GaSb and InSb. The growth of the nanoporous structure in the vertical direction was promoted until the ion dose was 1 × 10²¹ ions/m² or greater. At ion doses greater than 1 × 10²¹ ions/m², the growth was saturated. The wall thickness remained almost constant with increasing ion dose.

The interaction of iron (Fe) with defects induced by a high hydrocarbon-molecular-ion-implantation dose of 1 × 10¹⁶ cm⁻² in a Czochralski-grown silicon substrate and an epitaxial growth layer was investigated using secondary ion mass spectroscopy, transmission electron microscopy, and laser-assisted atom probe tomography (L-APT). High-dose hydrocarbon-molecular-ion-implantation formed two types of defects in the projection range: stacking faults and carbon agglomerates. It was demonstrated that the dominant gettering mechanisms of the two types of defects differ. Carbon agglomerates formed by implantation of the epitaxial growth layer exhibited high gettering efficiency for Fe. The L-APT data indicated that the Fe gettering efficiency is strongly affected by the distribution of oxygen atoms in carbon agglomerates. It is suggested that Fe gettering on agglomerates is due to the strong electronic interaction between carbon agglomerates and Fe but suppressed by oxygen atoms in agglomerates.