Table of contents

The photovoltaic industry is in a phase of rapid expansion, growing by more than 30% per annum over the last few decades. Almost all commercial solar cells presently use single-crystalline or multicrystalline silicon wafers similar to those used in microelectronics; meanwhile, thin-film compounds and alloy solar cells are currently under development. The laboratory performance of these cells, at 26% solar energy conversion efficiency, is now approaching thermodynamic limits, with the challenge being to incorporate these improvements into low-cost commercial products. Improvements in the optical design of cells, particularly in their ability to trap weakly absorbed light, have also led to increasing interest in thin-film cells based on polycrystalline silicon; these cells have advantages over other thin-film photovoltaic candidates. This paper provides an overview of silicon-based solar cell research, especially the development of silicon wafers for solar cells, from the viewpoint of growing both single-crystalline and multicrystalline wafers.

We investigated the effects of the oxygen flow rate (OFR) during the deposition of a zinc oxynitride (ZnON) channel layer on the electrical performance and stability of high-mobility ZnON thin-film transistors (TFTs). The ZnON TFTs prepared at a lower OFR exhibited higher electrical performance characteristics and a higher electrical stability under positive gate bias stresses than those prepared at a higher OFR, but showed a lower electrical stability under negative gate bias stresses. The lower density of subgap states within the channel layer and the higher hole concentration due to the small bandgap were considered as physical mechanisms responsible for the observed phenomena, respectively.

In this paper accurate measurements of temperature distribution on the facet of GaN-based diode lasers are presented as well as development of the instrumentation for high-resolution thermal imaging based on thermoreflectance. It is shown that thermoreflectance can be successfully applied to provide information on heat dissipation in these devices. We demonstrate the quantitative measurements of the temperature profiles and high-resolution temperature maps on the front facet of nitride lasers and prove that thermoreflectance spectroscopy can be considered as the accurate and fast nondestructive tool for investigation of thermally induced degradation modes of GaN lasers.

60 nm tunneling FET (TFET) based low noise amplifier (LNA) with a sub-0.5 V supply voltage for 2.4 GHz WSN application has been evaluated systematically from device level up to circuit level design. With the help of TFET's unique property of high subthreshold swing, it shows that substantial increase of gain performance was confirmed compared to that of conventional LNA using 60 nm bulk MOSFET at ultra-low voltage (ULV) condition. From the simulation study, TFET LNA at 0.4 V operating voltage has the gain of 15.1 dB and noise figure 50 of 3.5 dB while dissipating DC power consumption of 0.41 mW.

Heteroepitaxial BaTiO₃ ferroelectric films with (001), (110), and (111) orientations were grown on SrRuO₃-buffered SrTiO₃ substrates by magnetron sputtering. The leakage current and interface charge behaviors were systematically investigated. Without a discernible orientation-dependence behavior, the leakage current behaviors were all well described by a modified Schottky-contact model. On the basis of this theory, the interface charge state parameters, including dynamic dielectric constant, potential barriers, depletion layer width, effective space-charge density and hole concentration, and their evolution behaviors were analyzed in detail. They all exhibited anisotropic characteristics and were proved to be essentially attributed to the macrophysical properties of BaTiO₃ film heterostructures.

Strong room-temperature photoluminescence (PL) from SiO₂/Si(110)/SiO₂ quantum wells (QWs) is observed, for the first time. The PL intensity increases with the decrease of the Si(110) well thickness. Furthermore, when the upper SiO₂ layer is removed, no PL peaks could be observed. But the luminescence is recovered when the samples were exposed to air for several months with the re-formation of Si–SiO_x interface, and slightly dependent of temperature. These results indicate that both of the quantum confinement effect and the interface effect play an important role in the luminescence properties of Si(110) QWs.

We theoretically investigate two magnetic tunneling junctions (MTJs) with different semiconductor barriers, CuInSe₂ (CIS) and CuGaSe₂ (CGS), sandwiched between Fe electrodes. We find that Δ₁ wave functions provide dominant contributions to spin-dependent tunneling transport in both CIS- and CGS-based MTJs. We also find that the CGS-based MTJ has a much higher magnetoresistive (MR) ratio than the CIS-based MTJ, which indicates that a higher MR ratio is expected for a higher Ga concentration x in the recently reported CuIn_1−xGa_xSe₂-based MTJs. Furthermore, we show that the CIS- and CGS-based MTJs have much smaller resistance–area products (RA) than the conventional MgO-based MTJs.

The luminescence and scintillation properties of Tl- and Ce-doped Cs₂HfCl₆ crystals were investigated by photoluminescence and radioluminescence spectroscopy. In the photoluminescence spectra, emission bands of the activators were observed at 500 nm for Tl-doped Cs₂HfCl₆, and at 340 and 380 nm for Ce-doped Cs₂HfCl₆. The radioluminescence bands were observed at 405 and 430 nm for Tl- and Ce-doped Cs₂HfCl₆, respectively. Scintillation decay time constants for the Tl- and Ce-doped Cs₂HfCl₆ were smaller than those for the corresponding undoped crystals. Scintillation light yields for Tl- and Ce-doped Cs₂HfCl₆ were estimated to be 23,700 and 15,700 photons/MeV, respectively.

Superlattice thin films composed of iron chalcogenides, FeSe and FeTe, were grown via pulsed laser deposition. The X-ray diffraction patterns show clear satellite peaks demonstrating periodic stacking structures of FeSe and FeTe. The FeTe layers have the a-axis lengths identical to those of the FeSe layers, indicating that the FeTe layers are coherently strained to the underlying FeSe. The superlattice films show superconducting transition temperatures higher than FeSe, and more importantly the superconductivity emerged in several-unit-cell-thick layers. Our results demonstrate that the strained superlattice technique is a useful tool to control superconducting properties of Fe(Se,Te) thin films.

We propose that InGaN is superior to GaN as a host material for GaN-based red-light-emitting diodes (LEDs). In our previous paper, we proposed that codoping of Eu and a Mg and O pair generates an efficiently luminescent center in GaN. This is caused by the quantum confinement of the quantum dot constructions generated by the codoping method. The present report illustrates that InGaN allows the expansion of such electronic structures throughout the crystal owing to spontaneous phase decomposition. This can be used for self-organized fabrication and self-regenerated products.

Analytical models for threshold voltage and subthreshold swing of GaN-based fin-shaped field-effect transistors (FinFETs) are obtained. Analytical expressions for the drain-induced barrier lowering effect and threshold voltage roll-off effect are presented. The explicit expressions for threshold voltage and subthreshold swing make the model suitable for being embedded in circuit simulations and design tools.

We investigated band-profile control by introducing interlayers between a semiconductor and metal contact layers to improve the electrical properties of GaN-based semiconductor devices. We evaluated the electronic structure of the semiconductor surface and the metal/semiconductor interface by hard X-ray photoelectron spectroscopy. We also performed Monte Carlo simulations using the Boltzmann transport equation under the potential profile obtained using the Poisson equation. The band profile in the semiconductor substrate was then examined by comparing the energy spectra from the simulations with those from the experiments. We obtained good agreement between the two results. The present experimental and theoretical methods allow one to determine the band profile near the surface of a semiconductor as well as that in a metal interface. This approach may become a useful tool in the design and/or evaluation of processing conditions.

Li_yCoO₂ has a similar layered structure to Na_yCoO₂, which is a typical p-type oxide thermoelectric material, and the average Co valence of 3 + y is controlled by the Li content y. We investigated the thermoelectric properties of LiCo_1−xM_xO₂ samples (M = Cu, Mg, Ni, Zn) for the first time at high temperatures, in which Co³⁺ was substituted by the divalent M²⁺ ions, and the average Co valence of 3 + x can be controlled similarly to the Li content y in Li_yCoO₂. The substitution of the M²⁺ ions for the Co site was found to show thermoelectric properties similar to those of Li_yCoO₂ with the same average Co valence. The Mg-doped sample showed the highest thermoelectric performance at high temperatures in this study; the thermoelectric power factor P is 2.38 × 10⁻⁴ W m⁻¹ K⁻² at 1173 K and the dimensionless figure of merit ZT is 0.024 at 876 K. The thermoelectric potential of LiCo_1−xM_xO₂ is discussed and compared with those of Li_yCoO₂ and Na_yCO₂ systems.

We apply a hybrid quasiparticle self-consistent GW (QSGW) method, QSGW80+SO [Deguchi et al., Jpn. J. Appl. Phys. 55, 051201 (2016)], to a type-II superlattice, which is (InAs)_n(GaSb)_n (n = 1, 2, 3, and 4) for infrared sensors. For the first time, we successfully obtained reliable energy bands of the superlattice. The calculated band gaps as functions of n differ from those obtained on the basis of other theories, although they are consistent with the results of a recent photoluminescence experiment. Our real-space analysis of band-edge alignment obtained via core levels shows that the calculated band offset of InAs/GaSb for n = 4 is ∼0.5 eV, which is consistent with the value obtained in an X-ray photoelectron spectroscopy experiment.

Numerical calculations of the Gibbs function for an ordered assembly of BaTiO₃ nanocubes (nanocrystals) under three-dimensional clamping have revealed that the phase transition from a tetragonal to cubic crystal structure can take place at room temperature at some misfit strain associated with a tilt angle of the attached nanocubes. The phase transition is second-order due to the three-dimensional clamping. Near and at the phase transition, the dielectric constant becomes extremely high owing to the second-order transition. This is considered to be the reason for the high dielectric constant of an assembly at room temperature, which has been experimentally observed. An ordered assembly of BaTiO₃ nanocubes under rigid three-dimensional clamping is a completely different system from the normal nanocrystalline (polycrystalline) BaTiO₃ ceramics under elastic clamping and from a BaTiO₃ epitaxial thin film under two-dimensional clamping.

We developed a fullerene–ethylenediamine adduct (C₆₀P-DC) for a cathode buffer material in organic bulk heterojunction solar cells, which enhance the open-circuit voltage (V_oc). The evaporative spray deposition using ultra dilute solution (ESDUS) technique was employed to deposit the buffer layer onto the organic active layer to avoid damage during the deposition. By the insertion of a C₆₀P-DC buffer layer, V_oc and power conversion efficiency (PCE) were increased from 0.41 to 0.57 V and from 1.65 to 2.10%, respectively. The electron-only device with the C₆₀P-DC buffer showed a much lower current level than that without the buffer, indicating that the V_oc increase is caused not by vacuum level shift but by hole blocking. The curve fitting of current density–voltage (J–V) characteristics to the equivalent circuit with a single diode indicated that the decrease in reversed saturation current by hole blocking increased caused the V_oc.

This paper describes experimental and theoretical investigations of electronic and thermoelectric (TE) properties of high power factor sulfide Ni_1−xCo_xSbS (x = 0, 0.10, 0.20, and 0.40). For NiSbS, even in the metallic behavior, the power factor PF of NiSbS is 1.9 mW·K⁻²·m⁻¹ at 300 K, which exceeds the high performance TE sulfide materials as tetrahedrites or colusites. For the Ni_1−xCo_xSbS system, the residual electrical resistivity ρ_residual increases. However, the thermopower S decreases in comparison with NiSbS. For density functional theory (DFT) calculations, the chemical potential μ for NiSbS is located at the edge of the pseudo-gap in the electronic density of states (DOS). Electronic structure μ is located at the peak of PF, as understood by the large transmission R(E) and ∂R(E)/∂E at Fermi energy E_F for NiSbS. For Co-substitution, μ shifts to the valley of PF from the peak, indicating the importance of electron filling control for TE properties.

A wavelength selective switch is proposed for optical wavelength division multiplexing network applications with very short range interconnections. The proposed device uses a Mach–Zehnder interferometer configuration incorporating wavelength selective phase shifters composed of microring resonators between their two arms. Wavelength selectivity is provided by cascaded microring resonators, which are placed in proximity so that the increase in excess loss caused by the difference in resonant wavelengths can be minimized. An on/off switching ratio >20 dB is obtainable when the drop/through transmittance ratio of the cascaded microring resonators is >22 dB and the coupling efficiency deviation from 50% is <1% in the directional couplers constructing the Mach–Zehnder interferometer.

In this study, we developed a practical method to improve the optical performance of subwavelength antireflective two-dimensional (2D) gratings. A numerical simulation of both convex and concave paraboloids suggested that surface reflectivity drastically decreases when a step is introduced in the taper. The optimum height and depth of a step provided average reflectances of 0.098% for convex protrusions and 0.040% for concave protrusions in the visible range. Furthermore, a stepped paraboloid was experimentally fabricated by dry etching of a Si substrate with SiO₂ particle monolayer mask. A cyclo-olefin polymer (COP) reverse replica (concave) imprinted by the Si mold exhibited a measured reflectance of 0.077% on average in the visible range. It was also demonstrated that the antireflective structure was fabricated on the whole surface of a 6 in. Si wafer, which is a sufficient size for industrial utilization.

We investigated the surface reflectance of nanoimprinted textures on silicon. Zirconium oxide, which is a wide-bandgap inorganic dielectric material, was used as the texturing material. We performed several calculations to optimize the textures for the production of high-efficiency bulk-type monocrystalline silicon solar cells. Our analysis revealed that nanoimprinted textured solar cells exhibit a lower reverse saturation current density than a solar cell with a conventional etched texture. It was also confirmed that the photocarrier generation rate for a solar cell with a submicron-scale nanoimprinted texture has little dependence on the texture shape. Furthermore, the weighted average reflectance of an optimized nanoimprinted textured solar cell was substantially reduced to 3.72%, suggesting that texture formation by nanoimprint lithography is an extremely effective technology for producing high-efficiency solar cells at a low cost.

Wide gap n-type microcrystalline silicon carbide [µc-SiC:H(n)] is highly suitable as window layer material for silicon heterojunction (SHJ) solar cells due to its high optical transparency combined with high electrical conductivity. However, the hot wire chemical vapor deposition (HWCVD) of highly crystalline µc-SiC:H(n) requires a high hydrogen radical density in the gas phase that gives rise to strong deterioration of the intrinsic amorphous silicon oxide [a-SiO_x:H(i)] surface passivation. Introducing an n-type microcrystalline silicon oxide [µc-SiO_x:H(n)] protection layer between the µc-SiC:H(n) and the a-SiO_x:H(i) prevents the deterioration of the passivation by providing an etch resistance and by blocking the diffusion of hydrogen radicals. We fabricated solar cells with µc-SiC:H(n)/µc-SiO_x:H(n)/a-SiO_x:H(i) stack for the front side and varied the µc-SiO_x:H(n) material properties by changing the microstructure of the µc-SiO_x:H(n) to evaluate the potential of such stack implemented in SHJ solar cells and to identify the limiting parameters of the protection layer in the device. With this approach we achieved a maximum open circuit voltage of 677 mV and a maximum energy conversion efficiency of 18.9% for a planar solar cell.

I synthesized three bis-styrylbenzene derivatives substituted with typical electron-withdrawing groups: E,E-1,4-bis(4-trifluoromethystyryl)benzene (CF3), E,E-1,4-bis(4-cyanostyryl)benzene (CN), and E,E-1,4-bis(4-nitrostyryl)benzene (NO2). The photophysical and photoelectrical properties of these compounds were evaluated in detail. In free molecules in the solution, the intramolecular charge transfer interaction appeared in NO2. In the solid state of CN, the intermolecular charge transfer interaction was observed in its fluorescence spectrum. On the other hand, CF3 did not show intra- and intermolecular charge transfer interactions in either the solid or solution state. The ionization potentials of CF3, CN, and NO2 were −6.52, −6.09, and −6.38 eV, respectively, suggesting that the trifluoromethyl group was most effective for decreasing ionization potentials.

We have recently proposed a method of obtaining many spectral components of complex holograms under incoherent illumination. This method is based on the measurement of five-dimensional interferograms and signal processing including synthetic aperture processing. In this paper, we report the relationship between the selection rules used for synthetic aperture processing and the generated volume interferograms. As a result of our systematic study, we find six types of selection rule and generate volume interferograms that are the most important and basic. We discuss the benefits of using each selection rule and the three-dimensional (3D) imaging properties of retrieval imaging obtained from these volume interferograms. A new noise reduction method based on these six types of selection rules is also proposed.

The single-phonon mode was selectively excited in a solid-state sample. A mid-infrared free-electron laser, which was tuned to the target phonon mode, was irradiated onto a crystal cooled to a cryogenic temperature, where modes other than the intended excitation were suppressed. An A₁(LO) vibrational mode excitation on GaN(0001) face was demonstrated. Anti-Stokes Raman scattering was used to observe the excited vibrational mode, and the appearance and disappearance of the scattering band at the target wavenumber were confirmed to correspond to on and off switching of the pump free-electron laser and were fixed to the sample vibrational mode. The sum-frequency generation signals of the pump and probe lasers overlapped the Raman signals and followed the wavenumber shift of the pump laser.

Single-crystal diamond (SCD) has the potential to boost microelectromechanical system (MEMS) with unprecedented performance in terms of its intrinsic mechanical, chemical, and electronic properties, especially in the applications under extreme conditions. On the basis of the analysis of the energy dissipation in diamond mechanical resonators, the authors report on the marked improvement of the quality factor of SCD-MEMS resonators. Ion implantation assisted lift-off technique (IAL) is utilized to fabricate the SCD resonators. The quality factor of the resonator fabricated from the ion-damaged SCD layer alone is as low as 100–300 owing to the bulk or surface defects. The growth of homoepitaxial layers on the ion-implanted SCD substrates significantly improves the quality factor by more than 100 times. Cantilevers made of SCD epilayers of different thicknesses are examined. It is found that the quality factor increases with increasing the epilayer thickness. The maximum quality factor of the SCD cantilevers fabricated by the IAL technique reaches 3.9 × 10⁴. A bilayer model is proposed to describe the variation of the quality factor.

Effects of using asymmetric channel thickness in tunneling field-effect transistors (TFET) are investigated in sub-50 nm channel regime using two-dimensional (2D) simulations. As the thickness of the source side becomes narrower in narrow-source wide-drain (NSWD) TFETs, the threshold voltage (V_th) and the subthreshold swing (SS) decrease due to enhanced gate controllability of the source side. The narrow source thickness can make the band-to-band tunneling (BTBT) distance shorter and induce much higher electric field near the source junction at the on-state condition. In contrast, in a TFET with wide-source narrow-drain (WSND), the SS shows almost constant values and the V_th slightly increases with narrowing thickness of the drain side. In addition, the ambipolar current can rapidly become larger with smaller thickness on the drain side because of the shorter BTBT distance and the higher electric-field at the drain junction. The on-current of the asymmetric channel TFET is lower than that of conventional TFETs due to the volume limitation of the NSWD TFET and high series resistance of the WSND TFET. The on-current is almost determined by the channel thickness of the source side.

A one-port surface acoustic wave (SAW) resonator mass sensor composed of multilayer graphene (MLG) electrodes was investigated by the finite element method (FEM) and analyses were carried out to study the enhancement of sensitivity and the secondary effects caused by MLG electrodes on the performance of the resonator. Unlike metal electrodes, MLG electrode offers elastic loading to the contact surface, as evidenced by the increase in the surface velocity of the SAW device. In terms of the sensitivity of the mass sensor, MLG electrode showed the largest center frequency shift in response to a change in mass loading, as well as when used as a gas sensor to detect volatile organic compounds (VOCs). Also, MLG electrodes offered the least triple transit signal (TTS) and bulk acoustic wave (BAW) generations compared with Al and Au–Cr electrodes. Thus, the one-port SAW resonator with graphene electrodes not only possesses excellent performance characteristics but also gives rise to new opportunities in the development of highly sensitive mass sensors.

We studied the AC hysteresis loop and the harmonic spectra of samples containing immobilized magnetic nanoparticles (MNPs) at different values of the excitation field frequency f and amplitude H₀. First, we measured the dependences of the coercive field 〈H_c〉 on f and H₀. The measured dependences agreed qualitatively with the numerically predicted values. Next, we studied the relationship between 〈H_c〉 and the harmonic spectra, and found strong correlation between 〈H_c〉 and the attenuation rate of these harmonic spectra. We obtained an empirical expression for the harmonic spectra using 〈H_c〉 and a static magnetization curve for the immobilized MNPs. The expression obtained explained the experimental data well. Finally, the harmonic spectra were measured for two MNP samples with different distributions of the magnetic moment m. The MNP sample with the lower m distribution produces richer harmonic spectra for use in magnetic particle imaging.

We present a generalized theoretical analysis of the vibration of a micro/nano bridge resonator with a particle at an arbitrary location by considering the combined effect of the beam stiffness and string tension in the resonator. By combining resonant frequencies of at most three consecutive symmetric vibration modes, the developed model can unambiguously resolve the particle mass and position. The methodology is verified using published results. The finding is further validated numerically by finite element modeling using a microbridge with and without an added particle, which proves that the method resolves the particle mass and position with high accuracy.

We theoretically study the electronic structure of graphenes having several kinds of imperfections such as atomic vacancies and heteroatom replacements. We consider 12 different configurations of vacancies and 39 different geometries of heteroatom replacements in order to approximately take into account the random conformations of imperfections. To systematically provide a perspective understanding of the defect π and σ states caused by atomistic voids and/or vacancies and heteroatom replacements, we have carried out a tight-binding (TB) calculation. We study the orbital hybridization to clarify the origin and formation of π and σ defect states arising from such imperfections. We also discuss the electronic structure around the Fermi level through the TB band calculation.

Modulation of the thermal properties of graphene due to strain-induced phononic band engineering was theoretically investigated by first-principles calculations based on the density functional theory. The high-energy phonon modes are found to exhibit softening owing to the strain, whereas a low-energy acoustic mode (out-of-plane mode) exhibits hardening. Moreover, the dispersion relation of the out-of-plane mode associated with the strain essentially changes from quadratic (∝ k²) to linear (∝ k). Accordingly, the temperature dependence of the low-temperature specific heat also changes from linear (∝ T) to quadratic (∝ T²).

The physical properties of multiatomic vacancies are investigated by first-principles total-energy calculations. The formation energies of various vacancies as functions of chemical potential and charge states are calculated. The relationship between optimized atomic structures and charge states is analyzed. On the basis of the results, it is confirmed that the variations of formation energies and atomic structures are closely related to the changes in electronic states. In addition, the stabilities of generally large multiatomic vacancies are estimated on the basis of edges and corner energies. It is found that larger vacancies are not stable and have lower densities than smaller ones. The results are also compared with previous theoretical and experimental results.

AlGaInP is a prospectively valuable material for high-efficiency lattice-matched tandem AlGaInP/AlGaInAs/GaAs/GaInNAs/Ge (2.05/1.7/1.4/1.0/0.7 eV) five-junction solar cells. We examine the optical properties of AlGaInP materials with trimethylantimony (TMSb) incorporated at various flow speeds. Then, we apply Al_0.1GaInP with TMSb incorporated at 15.6 µmol/min, whose band gap is 2.04 eV, to the fabrication of an AlGaInP/Ge double-junction (DJ) solar cell. Moreover, we analyze the photovoltaic current density–voltage (J–V) characteristics, external quantum efficiencies (EQEs), and internal quantum efficiencies (IQEs) of DJ cells under a 1-sun AM0 spectrum. As elsewhere, Sb incorporation improves the crystal quality of AlGaInP and the fill factor of the DJ solar cell; on the other hand, it increases the band gap of AlGaInP. Al_0.08GaInP with Sb incorporation shows the same absorption edge of EQE as Al_0.1GaInP without Sb incorporation, and J_sc increases approximately by 15.3% owing to the reduction of 2% Al composition.

The crystalline microstructure of AlN films epitaxially grown on trench-patterned templates of AlN/α-Al₂O₃ and α-Al₂O₃ was studied by position-dependent X-ray microdiffraction measurements of AlN $11\bar{2}4$ and 0004 Bragg reflections. The crystalline microstructure of the AlN films is highly anisotropic and periodic corresponding to the periodicity in the trench pattern of templates. The lattice tilting fluctuation in the AlN film grown on the trench-patterned α-Al₂O₃ template is about one-half order of magnitude larger than that in the AlN film grown on the trench-patterned AlN/α-Al₂O₃ template. This is likely to be related to the significant misorientation initiated at the growth of AlN crystal domains from the sidewalls of the α-Al₂O₃ template without AlN buffer layers and the difference in contact areas at the AlN film/α-Al₂O₃ interface between the two samples. These findings suggest that trench-patterned templates of AlN/α-Al₂O₃ are suitable for growing thick high-quality AlN films.

We investigated the diffusion behavior of hydrogen in a silicon wafer made by a carbon-cluster ion-implantation technique after heat treatment and silicon epitaxial growth. A hydrogen peak was observed after high-temperature heat treatment (>1000 °C) and silicon epitaxial growth by secondary ion mass spectrometry analysis. We also confirmed that the hydrogen peak concentration decreased after epitaxial growth upon additional heat treatment. Such a hydrogen diffusion behavior has not been reported. Thus, we derived the activation energy from the projected range of a carbon cluster, assuming only a dissociation reaction, and obtained an activation energy of 0.76 ± 0.04 eV. This value is extremely close to that for the diffusion of hydrogen molecules located at the tetrahedral interstitial site and hydrogen molecules dissociated from multivacancies. Therefore, we assume that the hydrogen in the carbon-cluster projected range diffuses in the molecular state, and hydrogen remaining in the projected range forms complexes of carbon, oxygen, and vacancies.

A convenient procedure for preparing D-terminated Si(111)-(1×1) and Si(110)-(1×1) by wet chemical etching was developed and applied to the vibrational analysis of these surfaces by high-resolution electron-energy loss spectroscopy (HREELS). Fully H-terminated Si(111)/(110) was first prepared in regular 40% NH₄F/H₂O solution, followed by immersion in saturated KF/D₂O solution. HREELS revealed partially D-terminated H:Si(111)/(110) with the amount of deuterium termination depending on the immersion time. A series of various immersion times revealed the H/D exchange reaction kinetics, which are associated with the Si substrate etching processes on Si(111) (step-flow etching) and Si(110) (zipper reaction). The H–Si and D–Si stretching vibration frequencies as functions of the surface D fraction did not appear to change on Si(111), but on Si(110) the H–Si signal red shifted at a high D fraction. This is due to the adsorbate–adsorbate interaction, which is more intense on Si(110) because of the short nearest-neighbor distance of the adsorbates.

H, H₂, and SiH_x⁺ (x ≤ 4) ions coexist under plasma-enhanced chemical vapor deposition (PECVD) conditions. We have studied the kinetics of their interactions by high-level quantum chemical and statistical theory calculations, and compared the results with classical Langevin values (∼2 × 10⁻⁹ cm³ molecule⁻¹ s⁻¹ independent of temperature). The results indicate that, for H capturing by SiH_x⁺ (x ≤ 4), both theories agree within a factor of 2–4, whereas for H₂ capturing by SiH_x⁺ (x ≤ 3), the modern theory gives higher and weakly temperature-dependent values by up to more than one order of magnitude, attributable to reaction path degeneracies and increased entropies of activation. The heats of formation and structural parameters of SiH_x⁺ ions (x ≤ 5) in this work agree well with available experimental data. For practical applications, we have provided tables of rate constants for modeling various processes of relevance to the PECVD of a-Si:H films.

A new microwave plasma device system for in-line solution treatment is developed. In this system, the Venturi effect for pressure reduction is utilized for stable and effective plasma production. The decomposition of phenol solution is tested to verify the efficiency of an in-line plasma treatment system, and such a treatment system is confirmed to have a higher decomposition efficiency than our previously developed batch-type treatment system. Increases in phenol decomposition speed and decomposition energy efficiency with increasing solution flow rate are observed, which suggests the suppression of OH radical recombination and the utilization of OH radicals under flowing solution conditions.

In this paper, we report the formation of vertical GaN Schottky barrier diodes (SBDs) on a 2-in. free-standing (FS) GaN wafer, using CMOS-compatible contact material. By realizing an off-state breakdown voltage V_BR of 1200 V and an on-state resistance R_on of 7 mΩ·cm², the FS-GaN SBDs fabricated in this work achieve a power device figure-of-merit $V_{\text{BR}}^{2}/R_{\text{on}}$ of 2.1 × 10⁸ V²·Ω⁻¹·cm⁻² on a high quality GaN wafer. In addition, the fabricated FS-GaN SBDs show the highest I_on/I_off current ratio of ∼2.3 × 10¹⁰ among the GaN SBDs reported in the literature.

The minimization of plasma-induced damage (PID) in plasma etching is important for the precise and smooth removal of a depth of approximately 7 nm of GaN films to fabricate gate-recess GaN-based normally-off power electronic devices. We have systematically studied the photoluminescence (PL) properties and surface morphologies of GaN films exposed to Cl₂ plasma at 400 °C, focusing on their dependences on etch time and ion energy. It is noticeable that PL degradation saturated at etch times of more than 2 min, while surface roughness increased continuously with etch time. Variations of surface roughness with bias voltage were negligible. PID was successfully suppressed by reducing bias voltage, leading to the decrease in incident ion energy on the surface, and thus the near-band-edge emission (NBE) intensity as a PL property was increased to 98.8% of the initial value.

We investigated femtosecond-laser-induced modification at an Al/diamond interface. The interface was irradiated from the backside through the diamond substrate, which is transparent to the laser beam. Extremely high pulse energies, i.e., 200 and 100 µJ/pulse, were used to irradiate the interface. The cross-section of the laser-irradiated line was observed with conventional and high-voltage transmission electron microscopy. The modification of the laser-irradiated interface was characterized by the formation of an amorphous phase sandwiched between the deformed Al film and the diamond substrate. The major chemical component of the amorphous phase was identified as carbon, blown from the diamond substrate. The newly formed interface between the amorphous phase and the diamond substrate was concave. In addition, a fine ripple structure with an average spacing one-quarter the wavelength of the laser light was formed only in the sample irradiated by the higher-energy pulses.

We demonstrate and report the feasibility of utilizing terahertz (THz) surface emission from semiconductors as a mapping tool for magnetic field distribution. Using a standard THz time-domain spectroscopy setup, the THz emission of indium antimonide (InSb) was systematically measured at several different points of an external magnetic field. The initial results suggest promising directions in developing a practical THz emission-based magnetic field mapping technique for non-destructive electromagnetic imaging applications.

A preliminary reliability test was performed for lateral-current-injection GaInAsP/InP membrane Distributed Feedback (DFB) lasers fabricated by multi-regrowth and adhesive wafer bonding. The measurement was conducted for lasers with two different types of p-side electrode: Ti/Au and Au/Zn/Au. The device with the Au/Zn/Au electrode, which had better current–voltage (I–V) characteristics, showed no degradation of differential quantum efficiency and threshold current after continuous aging for 310 h at a bias current density of 5 kA/cm². This result indicates that the multi-regrowth and bonding process for the GaInAsP/InP membrane DFB laser will not impact the initial reliability.