Session Index

β-Ga₂O₃ thin films were grown on Al₂O₃(0006) substrates via MOCVD. Increasing growth temperature improved crystallinity, surface smoothness, and vertical grain alignment, as confirmed by XRD, SEM, AFM, and TEM. These findings highlight temperature’s key role in optimizing film quality for optoelectronic applications.

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Epitaxial β-Ga₂O₃ films were grown on c-plane Al₂O₃ by MOCVD to study the effect of TEGa flow rate on structural properties. XRD and TEM confirmed monoclinic single-crystalline growth along the <-201> orientation. Lower TEGa flow yielded smoother surfaces and growth rates of 6.14–13.5 nm/min.

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Several diamond-based-devices require producing, on a diamond substrate, a doped layer with a gradient of doping. The distortion of this layer can be important for the performance of the device.
We investigated, by using Rocking Curve Imaging (RCI), the distortion of a (100) platelet shaped, 250 µm thick, diamond crystal with two deposited boron-doped layers. This doping varies over 3.7 µm, is associated with a higher lattice parameter for the layer. This structure allows helping accommodating the variation of lattice parameter. Similar features were observed for other samples with 2 or 4 layers.




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Heteroepitaxial β-Ga2O3 films were grown by MOCVD on exact c-plane, 6° A-off-cut, and 6° M-off-cut sapphire. Gate-recessed enhancement-mode MOSFETs fabricated on the off-cut substrates show superior performance: the specific on-resistance drops from 1.85 kΩ·mm (c-plane) to 0.45 kΩ·mm (A-6°) and 0.70 kΩ·mm (M-6°); breakdown voltages reach 434 V, 584 V, and 442 V, respectively. The improvement is attributed to step-flow growth that guiding an ordered crystal arrangement during growth. These results demonstrate off-cut-driven substrate engineering as an effective route toward high-efficiency β-Ga2O3 power devices.

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We report a non-recess etch fabrication method for β-Ga2O3 MOSFETs that preserves the as-grown surface to eliminate plasma-induced damage. By increasing growth temperature of the N+/N- layers, silicon donor activation was enhanced, yielding higher free-carrier concentration. Devices exhibit increased on-state current, reduced on-resistance, improved field-effect mobility, also simplified the process. This fabrication approach enables high-performance β-Ga2O3 transistors for advanced wide-bandgap power electronics.

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Gallium oxide (Ga₂O₃), a promising ultra-wide bandgap (UWBG) semiconductor with a bandgap of ~4.9eV. In this study, we investigate the effect of different Schottky metal stacks on the electrical characteristics of Ga₂O₃-based Schottky barrier diodes (SBDs). By comparing pure Pt, Ni/Pt, and Ni/Au contacts, we examine the impact of adhesion, and potential interfacial reactions on turn-on voltage, leakage current, and on/off ratio. Devices with Pt contacts exhibit the best leakage suppression with an on/off ratio exceeding 10⁷, while Ni/Au structures suffer from severe leakage due to possible interfacial oxidation.

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In this study, a CO gas sensor based on β-Ga2O3 thin films was fabricated. The sensing performance was evaluated under photoactivation, using a xenon lamp as the excitation light source. Key characterization metrics included current–time response, resistance–concentration profiles, gas response percentages, linearity plots at various concentrations, response and recovery times. The results demonstrate that the β-Ga2O3 thin film exhibits excellent sensitivity and a strong linear correlation with CO concentration. The sensor achieved a rapid response time of 3.5 s; however, the recovery time was relatively long (11.1 s), primarily due to the influence of persistent photoconductivity induced by light illumination.

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A novel growth method for c-In2O3 was proposed, wherein In2O gas is selectively generated by supplying H2O vapor over In metal in the source zone. The c-In2O3 layer is formed via a reaction between the generated In2O gas and additional H2O gas in the growth zone. Thermodynamic analysis revealed that c-In2O3 growth using In2O and H2O gases is feasible at temperatures above 1000 °C. Based on the thermodynamic results, experimental growth was carried out, and c-In2O3 with (111)- and (100)-oriented domains were successfully obtained on sapphire (0001) substrates at 1000 °C.

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The Indium-Tungsten-Gallium Oxide thin films are applied to thin-film transistors using radio frequency magnetron sputtering. Silicon dioxide is used as the gate dielectric layer for the IWGO TFTs. T The IWGO TFTs are then subjected to light exposure measurements, showing a light-to-dark current ratio of 5.96 and rejection ratio of 9.98*10^2, confirming that IWGO TFTs can also be used in optoelectronic transistors.

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Chirality, like the distinction between left and right hands, prevents an object from overlapping with its mirror image. In optics, chiral structures enable selective polarization absorption, producing circular dichroism. Here, we present a high-performance dielectric metasurface of amorphous silicon on fused silica, combining chiral geometry with PB phase modulation to break symmetry between left- and right-handed circular polarization. This optically asymmetric, efficient design shows strong potential for multifunctional metalenses and next-generation devices like smartphone cameras and facial recognition systems.

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We propose a complex electric field optimization strategy to jointly optimize both amplitude and phase in the design of visible-light amorphous-silicon (a-Si) metalenses, significantly enhancing their efficiency. Numerical simulations and experimental validation on a polarization-independent NA = 0.2 lens demonstrate an approximate 30% improvement in focusing efficiency, highlighting the potential of this method to enable scalable production of high-performance metalenses for advanced optoelectronic, nanophotonic, and AR/VR applications.

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This work presents a successful implementation of the artificial intelligence (AI) model to inverse predict the input structural parameters of the silicon carbide (SiC) Trench MOSFET. Device structural parameters, such as trench depth, width, and angle, for 2.5kV breakdown voltage (BV) device were predicted successfully. For dataset, parameters of baseline 1.2kV BV device were varied to simulate more than 1600 instances to provide a sufficient dataset for the ML training. Technology Computer-aided Design (TCAD) has been used to simulate the device. The reinforcement learning (RL) based deep learning (DL) method has been implemented to inverse predict the parameters.

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Nitrogen (N) atoms doped in gallium oxide (Ga2O3) act as deep acceptors, and an energy barrier of about 3 eV can be formed at the N-doped p-Ga2O3/n-Ga2O3 junction. In this talk, we will present the effect of N radical irradiation on electrical properties of Ga2O3 Schottky barrier diodes and electrical properties of N-doped Ga2O3 thin films grown by molecular beam epitaxy.

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Diamond is an ultra-wide bandgap semiconductor material which has high critical electric field (10 MVcm-1), high carrier mobility (e:4500 cm2/Vs, h:3800 cm2/Vs), and excellent thermal conductivity (2200 Wm-1K-1). Therefore, the diamond-based power device is a next-generation promising semiconductor device platform that can be used in an extreme environment requiring ultra-high power and frequency performance. The most important issue to solve for commercialization is the small size and too high price of diamond.
In our study, the activities for the growth of large size single crystal diamond substrate have been conducting using the heteroepitaxy on the foreign substrate. In case of (100) plane, we achieved the heteroepitaxy of free-standing single crystal diamond wafer (size: 20x20 mm2) on the A-plane sapphire substrate in the last year [1-2], and are working on the heteroepitaxy of larger-size diamond wafer (>1inch).[3] Especially, the twin-free (111) single crystal diamond heteroepitaxy has been successfully demonstrated on the r-plane sapphire substrate, for the first time.[3]
In addition, the heteroepitaxial single crystal diamond-based device study has been successfully conducted in the area of doping and devices of p-SBDs and p-MESFETs [4-5].
Recently, the H-terminated diamond E-/D-mode MOSFETs have been simultaneously fabricated on the same heteroepitaxial diamond substrate [6].
The detailed advancements in the heteroepitaxial diamond wafer and power devices will be discussed in the conference.

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Epsilon Gallium oxide (ε(κ)-Ga2O3), a ferroelectric wide-bandgap semiconductor, is heteroepitaxially grown on silicon using TiN buffer via MOCVD. The TiN buffer layer enables epitaxial growth with reduced lattice mismatch, resulting in a ε(κ)-Ga2O3 film with preferred orientation. The temperature is critical for phase transformation and crystallinity of ε(κ)-Ga2O3. The Ga2O3 progresses from amorphous phase to epsilon phase, ending up with beta phase as the temperature increases. Furthermore, the enhanced crystallinity leads to improved ferroelectricity, showing a polarizability of 0.04 µC/cm2. The optimized conditions yielded high-quality ε(κ)-Ga2O3 films (XRD FWHM 0.111°, ~3% oxygen vacancies) with uniformity across 2-inch wafers.

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This work investigates the optical properties of (Al,Ga)N heterostructures emitting between 310nm and 209nm. Photoluminescence (PL) analyses were conducted on thick epilayers, single and multiple quantum wells. Full width at half maximum of the PL, orientations and shapes of the on-side emission diagram, and PL intensity were analyzed by taking into account valence band symmetry, Quantum Confined Stark Effect, and 2D carrier localization.
This work was supported by ANR funding GANEX (ANR-11-LABX-0014) and DOPALGAN .

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Ultra-wide bandgap AlGaN alloys are being investigated for the next generation of RF transistors due to their similar saturation velocity and high critical electric field, compared to GaN-based HEMT technology. However, the potential of AlGaN transistors has not been realized due to the difficulty in forming low-resistance contacts to the UWBG bandgap AlGaN alloys. We present a PolFET heterostructure that avoids the electron barrier due to the abrupt compositional change found in conventional HEMTs, allowing for lower contact resistance and enabling shielding of the charge in PolFET channel to achieve low sheet resistance and high mobility.

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This study aimed to enhance the sensing performance of nitrogen dioxide (NO2) gas sensors using gallium oxide (Ga2O3) nanorods grown on a roughened seed layer and forming more n-n homojunctions. The roughened seed layer was fabricated using a nanoimprint system with a grating period of 1000 nm. The response of the resulting NO2 gas sensor was significantly enhanced from 14.6 to 35.5 under a NO2 concentration of 10 ppm, and the optimal operating temperature was also decreased from 260 oC to 240 oC, indicating a substantial improvement in the sensing performance.

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We report on the direct growth of hexagonal boron nitride (hBN) on 4H-SiC by plasma-enhanced chemical vapor deposition (PECVD). The hBN layer is evaluated within a metal-insulator-semiconductor capacitor (MISCAP). Leakage current is 2.6 µA/cm^2, remaining unchanged after both negative and positive bias stress tests at 8 V for 1650 s. Capacitance-voltage measurements demonstrate good capacitance modulation with minimal dispersion from quasistatic to 1 MHz. The interface state density (Dit) was evaluated using both the high-low and C–ψ(s) methods, yielding a Dit of 4×10^11 cm^-2 ·eV^-1 and 9×10^11 cm-2 ·eV^-1, respectively.

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