Session Index

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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