Diamond-based devices are suitable for high-power, low power-loss, high-frequency, and high-temperature applications. Most of diamond-based metal-oxide-semiconductor field-effect transistors (MOSFETs) are fabricated on small-size diamond wafers $(3 \times 3\ \text{mm}^{2})$ . In order to promote the diamond-based devices for future applications, it is necessary to investigate the electrical properties of them on the large-area wafers. Here, we fabricate hydrogen-terminated diamond MOSFETs on a large-area wafer $(8\times 8\ \text{mm}^{2})$ with a quantity of 720. Electrical properties of them are investigated and discussed.

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 corresponding to the VC modes. In addition, the light source demonstrated selectivity to the enhanced emission wavelengths with changes in temperature. Compared to conventional dual-wavelength vertical external cavity surface-emitting lasers, these QD-based dual-wavelength emission devices allow for the realization of simple structures because the InAs QDs act as dual-light-emitting materials. These results can be applied to simple dual-wavelength surface-emitting light sources.

The ohmic contact resistance ( ${R}_{C}$ ), surface resistance ( ${R}_{S}$ ), and channel resistance ( ${R}_{\text {CH}}$ ) of hydrogen-terminated diamond (H-diamond) MOSFETs were investigated in this study. Planar-type and T-type H-diamond MOSFETs were employed to analyze them. Because no interspaces exist between the source–drain and gate electrodes for the T-type H-diamond MOSFETs, then ${R}_{S}$ is zero. Both planar-type and T-type MOSFETs show low leakage current densities and good operations. By considering the relationships between the total resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON}}$ ) and 1/ $\vert $ gate voltage-threshold voltage $\vert $ , ${R}_{C}$ and ${R}_{\text {CH}}$ for the T-type H-diamond MOSFET at a gate voltage of −10.0 V are determined to be 13.8 and 21.8 $\Omega \cdot $ mm, respectively. As ${R}_{C}$ for both MOSFETs is the same, ${R}_{S}$ and ${R}_{\text {CH}}$ for the planar-type H-diamond MOSFET are deduced to be 90.0 and 15.8 $\Omega \cdot $ mm, respectively. ${R}_{S}$ accounts for 75.3% of ${R}_{ \mathrm{\scriptscriptstyle ON}}$ for the planar-type H-diamond MOSFET, which is the main reason for its lower drain current and extrinsic transconductance than those of the T-type MOSFET. Although ${R}_{S}$ is suppressed for the T-type H-diamond MOSFET, ${R}_{C}$ occupies 38.8% of ${R}_{ \mathrm{\scriptscriptstyle ON}}$ . To further improve the performance of the H-diamond MOSFETs, it is important to eliminate ${R}_{S}$ and decrease ${R}_{C}$ to further improve the electrical properties of the H-diamond MOSFETs.

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 wavelength could be controlled by adjusting the time between the growth and capping of the As 2 -QDs. We utilized the multilayer stack of emission-wavelength-controlled As 2 -QDs to fabricate an electrically-driven light source and demonstrated its broadband (approximately 130 nm) emission in the 1–1.3 μ m wavelength range.

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 QDs growth conditions. This waveband is useful for obtaining a large imaging depth of OCT because of an optimal balance between absorption and scattering in biological samples. In addition, continuous tunable lasing in the waveband was achieved by introducing the QD-based gain chip into a grating-coupled external cavity. This tunable laser was introduced into an SS-OCT setup, and the point spread function (PSF) was evaluated. The PSF position was observed to vary according to the optical path length differences. These results demonstrate the feasibility of the application of emission-wavelength-controlled QDs for SS-OCT.

In this article, we report the fabrication and characterization of boron-doped diamond (B-diamond) Schottky diodes and MESFETs. Effects of annealing at 573-973 K on the electrical properties of these devices are investigated. Current densitymaximumfor the as-fabricated Schottky diode is 0.05 A/cm(2) at a gate voltage of -10.0 V. Annealing at 673 and 973 K makes it increase first to 0.70 A/cm(2) and decrease lately to 0.07 A/cm(2), respectively. ON/OFF ratios for the as-fabricated B-diamond Schottky diode exceed 4.5x10(8) at the OFF-voltage (V-OFF) of 0 V and 3.2 x 10(6) at V-OFF = 42.0 V. For the annealed Schottky diode, the ON/OFF ratios are higher than 1.7x10(6) at V-OFF < 6.0 V. Ideality factor and barrier height for Au/Pt bilayer gates on the B-diamond channel layer range from 1.05 to 1.78 and from 1.24 to 1.56 eV, respectively. All three B-diamond MESFETs with the gate lengths of 12.0, 7.0, and 4.3 mu m, respectively, operate with p-type channel characteristics. The drain current maxima for the as-fabricated MESFETs are -0.11, -0.16, and -0.39 mA/mm. After annealing at 773 K, these values increase to -0.17, -0.24, and -0.55 mA/ mm. Annealing at 773 K also increases the extrinsic transconductance maxima for the three MESFETs from 11.1, 11.0, and 10.4 mu S/mm to 18.6, 16.2, and 14.4 mu S/mm, respectively.

Optical coherence tomography with a visible broadband light source (vis-OCT) was developed for high-resolution and nondestructive measurements of semiconductor optical devices. Although a near-infrared (NIR) light source should be used for medical OCT to obtain deep penetration of biological samples, a visible broadband light source is available as a low-coherence light source for industrial products. Vis-OCT provides higher axial resolution than NIR-OCT, because the axial resolution of an OCT image is proportional to the square of the center wavelength of the light source. We developed vis-OCT with an axial resolution of less than 1 μm in air and obtained cross-sectional profiles and images of ridge-type waveguides having heights and widths of several μm. Additionally, we performed cross-sectional measurements and imaging of a stacked semiconductor thin layer. The measured values were similar to those measured by scanning electron microscopy, and the effectiveness of vis-OCT for nondestructive inspection of semiconductor optical devices was demonstrated.

Planar-type and novel triple-gate fin-type hydrogenated diamond (H-diamond) metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated on a single-crystalline diamond substrate. The ratio between the height of the lateral side and the width of planar side for each fin of the triple-gate MOSFETs was as high as 1.45. The leakage current densities at an electrical field strength of -1.5 MV cm(-1) for both the planar-type and triple-gate fin-type MOSFETs were around 10(-6) A cm(-2). Both MOSFETs operated well with on/off ratios as high as 10(10). The current output maximum normalized by the gate width of the triple-gate H-diamond MOSFET was -271.3 mA mm(-1), almost double that of the planar-type MOSFET. The results of this paper are expected to pave the way towards the fabrication of high current out and downscaled H-diamond MOSFETs.

We fabricated and characterized a grating-coupled external cavity laser with gain chips including self-assembled InAs quantum dots (QDs) for swept-source optical coherence tomography applications. By controlling the emission wavelength of the self-assembled InAs QDs, tunable lasing at a wavelength band of 1–1.1 μm was obtained, which represents an optimal balance between absorption and scattering in biological tissues. Straight and J-shaped edgeemitting ridge waveguides (RWGs) were fabricated on a GaAs-based waveguide layer containing four InAs QDs layers. A diffraction grating with the quasi-Littrow configuration was employed as an external cavity for the fiber-coupled diodes. Electroluminescence spectra from the QD-based diodes revealed that broadband amplified spontaneous emissions appeared in a J-shaped RWG, whereas Fabry–Perot lasing occurred in the straight RWG. The external cavity was then introduced for the diode with a J-shaped RWG, and a tuning range of 65 nm centered at approximately 1100 nm was obtained from the QD gain chip with the J-shaped RWG.

As a first step to develop a diamond integrated circuit, hydrogenated diamond not and nor logic circuits composed of depletion-mode (D-mode) and enhancement-mode (E-mode) metal-oxide-semiconductor field-effect transistors (MOSFETs) are fabricated. The D-and E-modes MOSFETs act as load and driver devices for the logic circuits, respectively, which provides complementary transistor actions. The extrinsic transconductance maxima for both the MOSFETs are almost the same value of 17 mS mm(-1) and insensitive to device processing. With supply voltage changing from -5 to -25 V, gain maximum for not logic circuit increases from 1.2 to 26.1. The nor logic circuit shows clear nor gate characteristics.

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 resolution of 0.69 mu m in air was obtained. This was effective for inspection of a transparent photoresist film with thickness of 1-2 mu m coated on a semiconductor wafer; the interface between the photoresist film and its substrate and the interface between the photoresist and air were resolved, and the film thickness was measured. In addition, the interface between an opaque epitaxially grown semiconductor layer (Al0.35Ga0.65As) and a GaAs substrate was also detected by vis-OCT. Here we propose a thickness-measurement technique that combines finite-difference time-domain simulation with vis-OCT. This method enables us to determine the thickness of even an optically absorbent epitaxial layer and offers a profile-measurement method that is particularly suitable for the fabrication of semiconductor optical devices. (C) 2016 The Japan Society of Applied Physics