We fabricated a GaN particle detector with a low-gain avalanche diode (LGAD) structure. The GaN detectors showed an ideality factor of 2.0 under forward bias, leakage currents less than 100 pA at -150 V, a differential specific on-resistance of 7 m Omega cm2, and the breakdown voltage of 473 V. For below-bandgap illumination, the gains at 50 degrees C at -100 V and -210 V were 2 and 25, respectively. Although avalanche multiplication in the gain layer was not dominant in the reverse current, we observed signals from an alpha particle and a Xe swift-heavy ion using the GaN detectors with LGAD structure, showing the excellent potential of GaN LGAD radiation detectors for applications in high-energy particle physics.

This work reports improved ohmic contacts on n-type AlN using a Zr/Al/Mo/Au metal stack with contact resistivities of similar to 10(-3) Omega & centerdot;cm(2) at 25(degrees)C and similar to 10(-5) Omega & centerdot;cm(2) at 500(degrees)C, which are over one and two orders of magnitude lower than Ti-based contacts, respectively. Temperature-dependent current-voltage characteristics reveal thermionic-field emission-dominated transport at the Zr/AlN interface, leading to improved conductivity and ohmic behavior above 400(degrees)C. Record-low specific on-resistance (R-on,R-sp) is achieved in AlN Schottky barrier diodes using Zr-based cathode compared to previously reported values at comparable breakdown voltages. The devices reveal 10 & times; enhanced Baliga Figure of Merit at 300(degrees)C and 500(degrees)C due to significantly lowered Ron,sp <50 m Omega & centerdot;cm(2).

Gallium nitride (GaN) is one of the wide-bandgap semiconductor materials, which may have an excellent radiation tolerance beyond silicon and therefore be usable as a charged-particle sensor in future high-luminosity hadron colliders with severe radiation environment. Aiming for a GaN sensor capable of detecting a minimumionizing particle, we prototyped and characterized a GaN-based low-gain avalanche diode (LGAD). While no breakdown was observed up to 200 V, formation of the gain layer was confirmed from the capacitance and collected charge (measured using 5.48 MeV alpha particles from a( 241)Am source) as a function of the bias voltage. Moreover, basic radiation tolerance with an extreme radiation fluence was evaluated using a simple GaN pn-diode irradiated with 50 MeV protons up to 1.1 & times; 10(16 )n(eq)/cm(2) . These results provide fundamental insight into the detailed understanding of the GaN-LGAD and radiation tolerance of the GaN detectors.

We demonstrated fully vertical heterojunction diodes (HJDs) featuring a Mg-doped AlN layer directly grown on an n-type 4H-SiC substrate by metal-organic chemical vapor deposition. The electrical activation of the Mg-doped AlN layer was performed at 900 degrees C. At room temperature, the specific contact resistivity of the Mg-doped GaN/Mg-doped AlN structure was 6 & times; 10-3 Omega cm2. In the AlN-on-SiC HJD, rectifying characteristics were obtained from 25 degrees C to 500 degrees C, exhibiting a rectification ratio exceeding 102. Reducing trap states and dislocations in the AlN layer would improve the device performance of the fully vertical AlN-based diodes.

Electron paramagnetic resonance (EPR) spectroscopy was used to investigate paramagnetic impurity centers in commercially available MgO single crystals at room temperature. Three dominant signals with resolved hyperfine structures were assigned to Mn-, V-, and Si-related centers based on their hyperfine patterns, angular dependences, and spin-Hamiltonian analysis. Angular-dependent measurements showed negligible anisotropy in the dominant resonance fields and hyperfine interactions, whereas weak Mn-related fine-structure components were reproduced by a cubic spin-Hamiltonian model. Sequential line-shape fitting and double integration enabled evaluation of representative g values, hyperfine constants, semi-quantitative spin concentrations, and effective spin-density ratios. The Mn-related signal is consistent with substitutional Mn 2+ in a nearly cubic environment, while the V-related signal is consistent with a nearly isotropic V 2+ -like center. The Si-related defect shows a much smaller hyperfine interaction, suggesting a spatially extended electronic state. These results provide a systematic EPR characterization of residual impurity centers in MgO substrates.

We grew GaN/InxGa1-xN superlattices (SLs) on GaN/sapphire substrates by atmospheric-pressure metal-organic vapor phase epitaxy (MOVPE) and determined the InxGa1-xN growth rate using high-resolution x-ray diffraction analysis. The use of SL structures substantially reduced the influence of strain relaxation, phase separation, and mixed 2D/3D growth modes, enabling reliable extraction of the effective GaN and InN growth rates within the alloy. By maintaining identical temperature, pressure, and gas-flow balance, we precisely estimated the individual growth rates and proposed a model that explicitly separates incorporation and desorption processes. For low-In composition (x(In) < 0.25), the GaN and InN rates exhibit negligible mutual interaction and depend solely on temperature under constant pressure and flow balance. The model successfully predicts InxGa1-xN growth rates using independent incorporation and desorption terms, and its applicability is confirmed for In vapor-phase ratios <0.7 and sufficiently high V/III ratios, while limitations are identified under excess-In or low-temperature conditions. These results provide practical guidelines for optimizing MOVPE growth, contributing to the efficient design of active and SL layers for high-power light-emitting diodes and green laser diodes.

Deep ultraviolet (DUV) photodetectors (PDs) based on ultra-wide bandgap semiconductor diamond-based have attracted extensive attention due to the immunity to solar light on the earth and thermal stability in extremely harsh environments. However, the preparation of a high-quality and high-purity single-crystal diamond epilayer remains a major obstacle to achieve high photo-response performance. Here, we demonstrate that diamond PDs with tunable photoresponse properties can be obtained on type-Ib diamonds through simple annealing in ambient H2 and a surface ozone treatment process. The surface holes and the nitrogen defects inside the type-Ib diamond work together to regulate the overall photoresponse performance. The responsivity of the PDs can be adjusted from 84.3 A W-1 to 2.65 x 104 A W-1, and the response time can be modulated from 42.5 s to less than 240 ms. The achievement of photo response performance modulation of PDs originates from the cooperative effect of deep natural nitrogen defects and surface states. Thus, our findings provide an alternative method and facile strategy for the tailoring of PDs' performance, which can meet different application requirements.

Hydrogen-terminated diamond field-effect transistors (FETs) using a hexagonal boron nitride (h-BN) gate insulator were fabricated on a diamond surface with reduced surface roughness in the direction of source/drain electrodes. The diamond surface was prepared on a mesa structure using chemical vapor deposition with a low methane concentration. The hydrogen-terminated surface was laminated with the h-BN gate insulator without air exposure to prevent the adsorption of atmospheric surface acceptors. The hydrogen-terminated diamond FET exhibited a high mobility of approximate to 1000 cm(2) V-1 s(-1) at room temperature. We performed theoretical analysis on the temperature and carrier density dependences of mobility, which suggested that Coulomb and surface roughness scattering were effectively reduced. The high mobility obtained in this study indicates the high potential of diamond as a semiconducting material. This study can contribute to the future development of diamond devices.

We fabricated arrays of circular, square, and triangular air holes in GaN by the conventional method using the electron beam lithography and reactive ion etching. The vertex radius of curvature for the square and triangular holes was reduced by shape modification. The minimum vertex radius of curvature for the 100-nm-size square and triangular holes were 17 and 11 nm, respectively.

The temperature increase of a thin film as a result of laser irradiation causes phase shift to the transmitted light. This phase shift can be quantitatively imaged by quantitative phase microscopy (QPM). Since the phase shift is a function of the thermal conductivity and thermo-optic coefficient (TOC), the recorded phase shift can be used to extract the thermal conductivity and TOC of the thin film by modeling the heat transfer within the thin film and its substrate. In this study, the laser-induced phase shift of three different transparent thin films deposited on transparent substrates is recorded by QPM. The thermal conductivity and TOC of the thin films obtained based on our heat transfer model show reasonable agreement with the values obtained from other methods. This method is simple yet cost-effective, which is advantageous compared with other available methods such as the thermoreflectance method.

Infrared near-field spectroscopy, or nano-FTIR, offers nanoscale resolution in three dimensions to probe the chemical and physical properties of samples, making it a unique characterization tool. This nanoscopic resolution in three dimensions is particularly suitable to probe a two-dimensional electron gas (2DEG) where a 2DEG has an effective thickness of a few nanometers and exists a few tens of nanometers below the capping layer. This work employs nano-FTIR spectroscopy to noninvasively probe the 2DEG of AlGaN/GaN heterostructures, which are crucial for high-power electronic devices and sensing applications. Higher harmonic amplitude and phase of the nano-FTIR spectra are sensitive enough to the carrier concentration of the 2DEGs, which is supported by analytical calculations based on the finite dipole model. A comparative analysis confirms that incorporating the 2DEG layer into the model is essential to matching spectral features with experimental observations. Furthermore, hyperspectral imaging of a cross-sectional sample provides a visual representation of the 2DEG. The findings demonstrate that nano-FTIR enables the characterization of 2DEG in AlGaN/GaN heterostructures with nanometric resolution under ambient conditions, hence expanding its applicability in the study of such systems.

This study employs the Williamson–Hall (W–H) models to examine the microstrains and crystallite sizes of CaCO3 occurring as calcite in limestone samples found in General Santos City and Sarangani Province, Southern Philippines. Using both the Uniform Deformation Model (UDM) and Uniform Stress Deformation (USDM) models, computations for average sizes were established to be identical, implying minimal strain influence. The consistency of resulting measurements extends to the microstrain, revealing uniform results for all samples. Correlation between crystallite sizes and microstrains in the calcite crystals was observed, where high-purity calcites exhibited larger crystallite sizes and microstrains. The crystallite sizes decrease with microstrains for calcites with higher Mg concentration, a finding that can be attributed to lattice distortion and the formation of defects. The release of stress forms these defects, thereby resulting in a reduction of microstrains. Moreover, the distinctly variable responses to strain exhibited by the samples could be influenced by either their anisotropic properties or other additional components. The W–H models, used jointly with UDM and USDM consistently predicted crystallite sizes, and thus offer valuable insights into the uniform stress responses of calcites. These promising results notwithstanding, USDM is shown to be especially relevant for anisotropic samples owing to the display deviations of crystallite sizes, a key feature of anisotropic natural calcites. The microscopic analysis is expected to provide additional understanding regarding the state of the limestone samples.

Achieving efficient low-voltage actuation of microelectromechanical system (MEMS) resonators in high-temperature environments poses a difficult topic due to the thermal interference and the risk of high-temperature failure. In this work, the single-crystal diamond (SCD) resonators fabricated through the ion implantation-assisted lift-off (IAL) technique exhibit a SCD-on-SCD cantilever structure. We propose an electrical actuation system based on the electrostatic effect specifically designed for SCD MEMS resonators with a low radio-frequency amplitude of similar to 100 mV. The SCD resonators demonstrate stable and efficient actuation across a wide temperature range, from room temperature to 500 degrees C. Importantly, the actuation voltage exhibits little impact on the resonance frequency and the Q factor of the resonator. The SCD resonator showcases exceptional thermal stability in resonance frequency, with a low temperature coefficient of frequency (TCF) below -12 ppm/degrees C up to 500 degrees C. The developed actuation scheme holds tremendous potential as a robust platform for realizing SCD MEMS devices, particularly in applications requiring high integration at high temperatures. An electrical actuation system harnessing the electrostatic effect is showcased for SCD MEMS resonators. In this setup, the electrode on the resonator is grounded, while the electrode on the SCD substrate, connected to an RF signal, is utilized to actuate the motion of the resonator. Notably, the SCD resonators exhibit reliable and efficient actuation across a wide temperature range, from room temperature to 500 degrees C.

GaN mesas were fabricated by sequential dry and wet etching of a +c-oriented GaN layer onto a lattice-matched AlInN layer for future applications of positive beveled edge termination, which is desirable for preventing premature breakdown of power devices. The dry etching produced hexagonal AlInN/GaN mesas surrounded by m-plane sidewalls with six protrusions at the vertices. The subsequent hot phosphoric acid etching selectively etched the AlInN layer to expose and etch the chemically unstable -c surface of the GaN layer, which formed reverse-tapered { 1012 } facets. The protrusions were sacrificed during the wet etching to prevent undesirable positive tapering at the vertices.

While physical reservoir computing (PRC) is a promising way to achieve low power consumption neuromorphic computing, its computational performance is still insufficient at a practical level. One promising approach to improving PRC performance is deep reservoir computing (deep-RC), in which the component reservoirs are multi-layered. However, all of the deep-RC schemes reported so far have been effective only for simulation reservoirs and limited PRCs, and there have been no reports of nanodevice implementations. Here, as the first nanodevice implementation of Deep-RC, we report a demonstration of deep physical reservoir computing using an ion gating reservoir (IGR), which is a small and high-performance physical reservoir. While previously reported Deep-RC scheme did not improve the performance of IGR, our Deep-IGR achieved a normalized mean squared error of 0.0092 on a second-order nonlinear autoregressive moving average task, with is the best performance of any physical reservoir so far reported. More importantly, the device outperformed full simulation reservoir computing. The dramatic performance improvement of the IGR with our deep-RC architecture paves the way for high-performance, large-scale, physical neural network devices.

We demonstrated fully vertical Schottky barrier diodes (SBDs) that have a Si-doped AlN drift layer directly grown on an n-type 4H-SiC substrate by metal-organic CVD. The AlN SBD with a Ni anode showed a clear rectifying characteristic at 300-500 K and a rectification ratio of about 10-2. We found that the leakage current of the vertical AlN-on-SiC devices is affected by defects in the AlN drift layer and Schottky interface.

Physical reservoir computing (PRC) is useful for edge computing, although the challenge is to improve computational performance. In this study, we developed an inverted input method, the inverted input is additionally applied to a physical reservoir together with the original input, to improve the performance of the ion-gating reservoir. The error in the second-order nonlinear equation task was 7.3 x 10-5, the lowest error in reported PRC to date. Improvement of high dimensionality by the method was confirmed to be the origin of the performance enhancement. This inverted input method is versatile enough to enhance the performance of any other PRC.

Alkaline earth (AE) metal-alloyed SnS films with a bandgap of 1.8 eV were demonstrated to us promising for their use in widegap photovoltaic absorbers by forming a p-n junction with an n-type CdS layer. The Ba-alloyedSnS film exhibited the highest efficiency among the three types of AE-alloyed SnS films (barium, calcium, and strontium alloyed-SnS films). Electricity generation by the formation of the junction of p-AE-alloyed SnS/n-CdS indicates the possibility of realizing Si-based tandem solar cells.(c) 2023 The Ceramic Society of Japan. All rights reserved.

The electrical response of the electric double layer (EDL) effect at the interface between a hydrogen-terminated diamond (H-diamond) and a Li+-conducting solid electrolyte [i.e., LiNbO3 and Li3PO4] was investigated by using an all-solid-state H-diamond-based EDL transistor (EDLT). A 5-nm-thick LiNbO3 or Li3PO4 interlayer was inserted between a H-diamond and a Li-Si-Zr-O (700 nm) Li+ solid electrolyte. We performed Hall measurements and pulse response measurements to investigate the EDL charging characteristics exhibited. The Hall measurements evidenced that all EDLTs exhibited EDL-induced hole density modulation, with a large EDL capacitance (CEDL) to 15 mu F/cm2 in the Li +-deficient region (negative VG side). On the other hand, in the pulse response measurement, insertion of an LiNbO3 or Li3PO4 interlayer caused significant acceleration/deceleration of the switching response speed, ranging from tau = 61.4 ms to 229 mu s? CEDL at the LiNbO3/H-diamond and Li3PO4/H-diamond interface, particularly on the Li+ rich side, was indicated as determining the switching response speed. The results indicate that the very thin EDL (i.e., 5 angstrom) can be formed at the solid/solid electrolyte interface, even when inorganic solid electrolytes are used instead of liquid electrolytes, and CEDL at the solid/solid electrolyte can be controlled by electrolyte compositions within a thickness of several angstrom from the interface.