Naoki Ikeda

• National Institute for Materials Science

We present our recent development of the surface-emitting quantum cascade laser with a PC (photonic crystal) resonator and a strain-compensated MQW (multiple quantum well) active layer operating at around 4.3 μm. We describe the laser performance mainly from the viewpoint of the design and analysis of the PC resonators, which include both numerical...

We successfully fabricated silicon-on-insulator (SOI) photonic crystal (PhC) slabs in which electromagnetic topological band gaps and edge modes were materialized for symmetric transverse-electric-like modes. Because the structure of our specimens can be regarded as symmetric about the horizontal middle plane of the PhC slab, their symmetric and an...

High-quality emission centers in two-dimensional materials are promising components for future photonic and optoelectronic applications. Carbon-enriched hexagonal boron nitride (hBN:C) layers host atom-like color-center (CC) defects with strong and robust photoemission up to room temperature. Placing the hBN:C layers on top of Ag triangle nanoparti...

We propose and numerically investigate integrated photonic crystal waveguides (PhC-WGs) formed in a semiconductor slab to realize an ultrasmall and highly efficient terahertz (THz) wave source. The structure consists of a straight PhC-WG with low-group-velocity and low-dispersion (LVLD) for efficient difference frequency generation (DFG) connected...

We realized a wide-band wavelength conversion method through four-wave mixing in W3-type AlGaAs photonic crystal waveguides. AlGaAs exhibits a large third-order nonlinearity. Furthermore, because of its large bandgap, two-photon absorption can be avoided in the 1550-nm range. A four-wave mixing efficiency of −9.03 dB was obtained for a pump peak po...

High-quality emission centers in two-dimensional materials are promising components for future photonic and optoelectronic applications. Carbon-enriched hexagonal boron nitride (hBN:C) layers host atom-like color-center (CC) defects with strong and robust photoemission up to room temperature. Placing the hBN:C layers on top of Ag triangle nanoparti...

We report on the first experimental observation of two-dimensional isotropic double Dirac cones in the electromagnetic dispersion relation, which were materialized by the accidental degeneracy of E1- and E2-symmetric eigenmodes on the Γ point of photonic crystals. We fabricated triangular-lattice photonic crystal slabs of the C6v symmetry on silico...

We developed a compact dual-wavelength surface-emitting light source using InAs quantum dots (QDs) embedded in a vertical cavity (VC). The VC was designed to possess two optical cavity modes that resonate with the discrete emission lines of the QDs. The fabricated light source exhibited significant enhancements in the vertical light emission corres...

We fabricated surface-emitting quantum cascade lasers with photonic crystal resonators whose active layers were strain-compensated InGaAs/AlInAs multiple quantum wells to operate at 4.3 μm. We tested two kinds of square-lattice photonic crystals consisting of circular and pentagonal InGaAs cylinders as a unit structure. We examined their output pow...

We study the angle-dependent reflection spectra of two-dimensional photonic crystal (PC) slabs, which we use for developing mid-infrared surface-emitting lasers. The PC design produces a perfect resonance between material gain frequencies and the [Formula: see text]-point band edge in the first Brillouin zone. Hence, we expect laser emission to occ...

A newly developed oxide scale sublimation chemical vapor deposition (OSSCVD) technique for 2D MoS2 growth is reported. Gaseous MoO3, which is supplied separately from H2S, can be generated in situ by flowing O2 over Mo metal with oxidation and sublimation processes. In this method, particularly, controllably and abruptly modulating the supply of Mo...

We investigated the growth per cycle (GPC) for SiO2 and HfO2 on n-GaN/native oxide and p-Si/SiO2 substrates by plasma-enhanced atomic layer deposition using tris(dimethylamino)silane and tetrakis(dimethylamino)hafnium precursors, respectively, and O2 plasma gases. On the basis of the estimated GPC, we also examined the characteristics of n-GaN/Hf0....

Photonic crystal resonators with the C 4v symmetry were designed and fabricated on quantum cascade lasers with a strain-compensated multiple quantum well to achieve single-mode and vertical surface emission at 4.32 μ m. Their fabrication accuracy was confirmed by high-resolution reflection spectroscopy. The maximum output power was 10 mW at 77 K. A...

Photonic crystals (PCs) offer unique ways to control light-matter interactions. The measurement of dispersion relations is a fundamental prerequisite if we are to create various functionalities in PC devices. Angle-resolved spectroscopic techniques are commonly used for characterizing PCs that work in the visible and near-infrared regions. However,...

We measured angle-resolved reflection spectra of triangular-lattice photonic crystal slabs fabricated in a silicon-on-insulator wafer in the mid-infrared region. We achieved a high angle-resolution measurement by means of our homemade optical setup integrated in the sample chamber of an FT-IR spectrometer. By examining the reflection peak frequency...

Photonic crystals (PCs) offer unique ways to control light-matter interactions. The measurement of dispersion relations is a fundamental prerequisite if we are to create novel functionalities in PC devices. Angle-resolved spectroscopic techniques are commonly used for characterizing PCs that work in the visible and near-infrared regions. However, t...

In this study, an optical gain chip using emission-wavelength-controlled self-assembled InAs quantum dots (QDs) was developed for swept-source optical coherence tomography (SS-OCT) applications. The optical characterizations indicated that the QDs emission wavelength and optical gain spectra were controlled in the 1.1 μ m waveband by optimizing the...

Herein, we report an emission wavelength control technique for self-assembled InAs quantum dots (QDs) grown via molecular beam epitaxy using an As 2 source (As 2 -QDs). The As 2 -QDs exhibited photoluminescence with a shorter center wavelength and larger bandwidth than those of the QDs grown using an As 4 source. In addition, the emission center wa...

To clarify a factor on the reliability, we investigated the characteristics of carbon-doped indium oxide (InO 1.16 C 0.04 ) thin-film transistors by varying the O 2 concentration from 0.001% to 100% at atmospheric pressure under negative bias stress (NBS) and positive bias stress (PBS). A positive threshold voltage ( V th ) shift was observed when...

Characteristics of thin-film transistors (TFTs) with amorphous In 2 O 3 (InO 1.2 ) and carbon-doped In 2 O 3 (InO 1.16 C 0.04 ) channels by post-metallization annealing (PMA) process were investigated. The InO 1.2 TFT changed from metallic to switching behavior after PMA at 200 °C. In contrast, the InO 1.16 C 0.04 TFT exhibited superior properties...

Interface characteristics of frequency dispersion, flatband voltage (Vfb) shift, fixed charge (QIL), and interface state density (Dit) in β-Ga2O3/Al2O3/Pt capacitors were investigated after postmetallization annealing (PMA) at 300 °C in N2 using a conductance method and a photo-assisted capacitance-voltage technique. After PMA, no frequency dispers...

1. Introduction The resistive random access memory (ReRAM), which is a nonvolatile memory device, on flexible plastic substrate have been widely investigated for future wearable device. The flexible ReRAM based on metal-insulator-metal (MIM) structure is generally fabricated at relatively low temperature (~250°C) from the viewpoint of heat resistan...

The dispersion relation and the angle-resolved reflection spectra of triangular-lattice photonic crystal slabs of the C6v symmetry were examined by the finite element method. The Dirac-cone dispersion relation on the Γ point of the reciprocal space was confirmed. The reflection spectra showed unique selection rules that agreed with the analytical c...

Fourier transform (FT) spectroscopy is a versatile technique for studying the infrared (IR) optical response of solid-, liquid-, and gas-phase samples. In standard Fourier transform infrared (FT-IR) spectrometers, a light beam passing through a Michelson interferometer is focused onto a sample with condenser optics. This design enables us to examin...

The growth rate of an SiO2 film on various metal–oxide (M–O) underlayers by plasma-enhanced atomic layer deposition (ALD) using tris(dimethylamino)silane precursor and O2 plasma gas is systematically investigated, and the effect of the difference in the electronegativity of the M–O underlayer on the ALD-SiO2 growth mechanism is also discussed. All...

Fourier transform (FT) spectroscopy is a versatile technique for studying the infrared (IR) optical response of solid-, liquid-, and gas-phase samples. In standard FT-IR spectrometers, a light beam passing through a Michelson interferometer is focused onto a sample with condenser optics. This design enables us to examine relatively small samples, b...

We materialized the isotropic Dirac-cone dispersion relation in the mid-infrared range by fabricating photonic crystal slabs of the C4v symmetry in SOI (silicon-on-insulator) wafers by electron beam lithography. The dispersion relation was examined by the angle-resolved reflection spectra with our home-made high-resolution apparatus, which showed a...

Introduction In 2 O 3 -based metal oxide semiconductors have been widely investigated as active channel materials for oxide thin film transistors (TFTs) in flexible devices. The bond dissociation energy (BDE) between metal and oxygen element in the In 2 O 3 -based metal oxide has been recently focused because a low BDE easily occurs excess oxygen v...

Interfaces in Al2O3/n-GaN capacitors fabricated on free-standing GaN substrates were investigated using sub-bandgap photo-assisted capacitance-voltage measurements. After post-metallization annealing (PMA) at 300 °C, the metal-oxide-semiconductor (MOS) devices exhibited excellent capacitance-voltage (C-V) characteristics without frequency dispersio...

We investigated the characteristics of n-GaN/Hf0.64Si0.36Ox/Pt MOS capacitors fabricated by post-deposition annealing (PDA) at 800 °C in O2 (PDO), N2 (PDN), and 3%H2 (PDH) ambients. After PDO, the Hf0.64Si0.36Ox film was partially crystallized and had a thick interfacial layer (6.3 nm) at the n-GaN/Hf0.64Si0.36Ox interface, while the Hf0.64Si0.36Ox...

We investigated the influence of post-deposition annealing (PDA) temperature on the characteristics of Pt/Al2O3/n-β-Ga2O3 MOS capacitors. Electrical properties such as the flatband voltage (Vfb) shift, Vfb hysteresis, fixed charge (QIL), interface state density (Dit) and leakage current could be divided into two groups such as a low PDA temperature...

A ferroelectric HfxZr1−xO2 (HZO) thin film crystallized with nanocrystalline top- and bottom-ZrO2 nucleation layers (D-ZrO2) exhibited superior remanent polarization (2Pr = Pr⁺ − Pr⁻ = 29 μC/cm²) compared to that of similar thin films (12 μC/cm²) crystallized without a ZrO2 nucleation layer (w/o) when the HZO film thickness was 10 nm. Epitaxial-lik...

We investigated the characteristics of 10-nm-thick ferroelectric Hf0.43Zr0.57O2 (HZO) thin films fabricated using plasma-enhanced atomic layer deposition (PE-ALD) at 300 °C with plasma O2 gas and a post metallization annealing (PMA) process at 300–400 °C. The as-grown HZO film had a nanocrystalline structure (5–10 nm) with ferroelectric orthorhombi...

We developed a near-infrared (NIR) superluminescent diode (SLD) based on self-assembled InAs quantum dots (QDs) and demonstrated high-axial-resolution optical coherence tomography (OCT) imaging using this QD-based SLD (QD-SLD). The QD-SLD utilized InAs QDs with controlled emission wavelengths as a NIR broadband light emitter, and a tilted waveguide...

This work investigated characteristics of Al2O3/native oxide/n-GaN MOS capacitors by post-metallization annealing (PMA). A native oxide interlayer which composed of ε- and γ-Ga2O3 phases (Native oxide) and the reduced amount of one (Reduced) on n-GaN were prepared by cleaning only a sulfuric acid peroxide mixture (SPM) and both SPM and buffered hyd...

Characteristics of hafnium silicate as gate dielectric in n-GaN capacitors were investigated. The Hf0.57Si0.43O x , Hf0.64Si0.36O x and HfO2 films exhibited high dielectric constants of 15.4, 15.9, and 17.6, respectively. The Hf0.57Si0.43O x and Hf0.64Si0.36O x films, which had an amorphous structure, showed superior properties, including a minimal...

It has been believed that the energy transfer of one exciton arising in an organic layer creates one SPP on a proximally-positioned metal surface. However, because excitons in the organic layer are close to one another, there is the possibility that multiple SPPs are generated in phase, entering an appearance of constructive interference among the...

We demonstrated non-destructive and non-contact measurement of semiconductor optical waveguide using optical coherence tomography with a visible broadband light source (vis-OCT). Vis-OCT can provide high axial and lateral resolutions of less than 1 µm, which were effective for measurement of optical waveguides with several-micrometer structure. We...

Recently, Hf x Zr 1−x O 2 (HZO) thin films have been widely investigated to achieve low power device applications such as ferroelectric random access memory (FeRAM) and ferroelectric field effect transistor (FeFET), due to its stable ferroelectricity even in extremely thin region (~10 nm) and CMOS applicability [1]. Moreover, matured atomic layer d...

Introduction Bottom-gate-type thin-film transistors (TFTs) have an advantage of active channel protection because the In-Si-O-C channel can be formed in the final fabrication process. However, it still remains a big issue of poor stability because the back-side surface of the In-Si-O-C channel is directly exposed to the environmental conditions, an...

We have investigated characteristics of Al2O3 thin films, which are deposited by plasma-enhanced atomic layer deposition (PE-ALD) and thermal ALD (TH-ALD) with oxygen plasma and H2O as oxidant gas, respectively, and Al(CH3)3 precursor. The Al2O3 film, which was deposited at 50℃, exhibited a large leakage current property. The positive (~10¹⁸ cm－3)...

We report the first experimental finding of nonlinear responses of photoluminescence (PL) intensity in coupling systems of plasmonic metasurface and InAs quantum dots (QDs) embedded in a GaAs substrate. We numerically designed the coupling systems and experimentally studied the PL at room temperature (RT). We found that even weak excitation induces...

Light--matter interaction exploiting plasmons is attracting great interest in terms of a new twist, hot electrons. We designed a basic configuration to couple plasmonic metasurfaces with a layer of quantum dots (QDs) embedded in semiconductors and experimentally investigated the photoluminescence (PL) dynamics in the coupled systems of III-V semico...

The effect of crystallized ZrO2 (ZrO2-seed), amorphous Hf0.43Zr0.57O2 (HZO; HZO-seed), and amorphous Al2O3 (Al2O3-seed) seed layers on the ferroelectricity of HZO films was investigated. The remanent polarization () of a TiN-electroded capacitor with a ZrO2-seed layer was much larger than that of capacitors with a HZO-seed, Al2O3-seed, or no seed l...

We herein propose and verify an ultra-small near-infrared (NIR) multi-wavelength light source using a heterojunction photonic crystal waveguide (PC-WG) and quantum dots (QDs). A heterojunction two-dimensional PC-WG, which consists of multiple PC-WGs with sequentially shifted structural parameters, is fabricated on a GaAs-slab including InAs QDs. Sp...

We obtained a high-intensity and broadband emission centered at ~1 μm from InGaAs quantum three-dimensional (3D) structures grown on a GaAs substrate using molecular beam epitaxy. An InGaAs thin layer grown on GaAs with a thickness close to the critical layer thickness is normally affected by strain as a result of the lattice mismatch and introduce...

We developed a spectral-domain optical coherence tomography (OCT) using a visible broadband light source (vis-OCT) for application to high-resolution and nondestructive profile measurement and imaging in semiconductor optical-device fabrication. By using visible broadband light centered at 625 nm and with spectral bandwidth of 260 nm, an axial reso...

InAs quantum dots (QDs) were grown on GaAs by molecular beam epitaxy using As 2 molecules (As 2 -QDs) and were structurally and optically characterized. Photoluminescence (PL) measurements revealed unique optical properties of the As 2 -QDs, which differ from InAs QDs grown with As 4 (As 4 -QDs). As 2 -QDs exhibited PL emission centered at 1.14–1.2...

The optical properties of arrays of nanoholes and nanoslits in Al films were investigated both numerically and experimentally. The choice of Al was based on its low cost and ease of processing, in addition to the fact that it has a higher plasma frequency than gold or silver, leading to lower optical losses at wavelengths of 400 to 500nm.

We developed an electrically driven near-infrared broadband light source based on self-assembled InAs quantum dots (QDs). By combining emissions from four InAs QD ensembles with controlled emission center wavelengths, electro-luminescence (EL) with a Gaussian-like spectral shape and approximately 85-nm bandwidth was obtained. The peak wavelength of...

We report a broadband-gain superluminescent diode (SLD) based on self-assembled InAsquantum dots(QDs) for application in a high-resolution optical coherence tomography(OCT) light source. Four InAsQD layers, with sequentially shifted emission wavelengths achieved by varying the thickness of the In0.2Ga0.8As strain-reducing capping layers, were embed...

We developed a spectral-domain optical coherence tomography (SD-OCT) with a white light source for high-resolution, non-destructive profile imaging. By using a 625-nm-centered white light (260 nm bandwidth), 0.69 /nm of axial resolution was achieved. This resolution is suitable for the inspection of thin photoresists (e.g., 1–2 μm) coated semicondu...

Optical electric field enhancement in the normal direction was experimentally investigated using mid-infrared slot antennas that were formed on a thin Al2O3 layer/Si substrate. The Al2O3 layer thicknesses could be controlled to an accuracy of a given atomic layer through the use of atomic layer deposition, and varied from 0 nm to 60 nm. An in-depth...

Photonic crystals (PhCs) composed of β-FeSi2 with amorphous Si (a-Si) cladding layers are systematically studied to realize silicon photonics devices incorporating Si-based light-emitting layers. The bandgap characteristics of two types of triangular-lattice-type PhC in the telecommunication wavelength region of approximately 1.55 µm are calculated...

We developed a low-coherence light source based on self-assembled InAs quantum dots (QDs) with controlled emission wavelengths and applied it to optical coherence tomography (OCT) imaging. A current-driven superluminescent diode (SLD) light source including four layers of QDs exhibits a broadband (80-nm-bandwidth) emission centered at approximately...

We experimentally demonstrate a TiO2 double-groove grating coupler with two different groove widths on a SiO2 substrate in the visible region. Tolerance investigations based on Bloch-mode profiles in the grating and coupling strengths between the Bloch modes and diffraction orders reveal that the transmission performance is robust when one of the p...

Near-infrared (NIR) light sources are widely utilized in biological and medical imaging systems owing to their long penetration depth in living tissues. In a recently developed biomedical non-invasive cross-sectional imaging system, called optical coherence tomography (OCT), a broadband spectrum is also required, because OCT is based on low coheren...

The electric field in the normal direction was experimentally investigated by using mid-infrared antennas that were formed on a thin Al2O3 layer/Si substrate. The Al2O3 layer could be as thin as a single nm-order employing the atomic layer deposition, and was varied from 2 nm to 50 nm. The field distribution was estimated by observing the reflectiv...

We demonstrate tunable, enhanced 0th-order transmission through a metal–dielectric nanohole array device with a subwavelength-thick liquid crystal (LC) layer. The LC filled the nanoholes and formed a subwavelength covering layer, which is then capped by a top cover layer. The wavelength where the transmittance dip associated with the LC occurs is d...

A near-infrared superluminescent diode (SLD) using stacked InAs/GaAs quantum dots (QDs) was developed. The emission wavelength of each QD layer was controlled by varying the thickness of a strain-reducing layer deposited on the QD. The controlled ground state emission peaks enabled formation of a dipless broadband spectrum with the contributions of...

Optical tuning of extraordinary optical transmission (EOT) through a metallic hole array is achieved using an azobenzene dye-doped nematic liquid crystal. The liquid crystal is aligned homeotropically on the hole array and is sandwiched by a counter substrate placed at a distance of approximately 1 mu m from the hole array. Upon UV irradiation, the...

A subwavelength hole array, which consists of a thin metallic film and a dielectric, enables to transmit a certain wavelength caused by surface plasmon polaritons (SPPs). SPPs exist at the interface between the metal and the dielectric, which means that the transmission spectrum strongly depends on the propagation of SPPs across the material interf...

We have grown a stack of In-flushed InAs quantum dot (QD) layers to realize a broadband emission centered at ∼1 µm with a Gaussian-like spectrum as a light source for optical coherence tomography (OCT). The In-flush process, which enables control of the height of the QD, was optimized to control the emission wavelength and intensity of self-assembl...