Periodic metallic gratings on substrates can support a range of electromagnetic modes, such as leaky waveguide, guided-resonant, and Fabry-P & eacute;rot cavity modes, which can strongly modulate optical transmission under resonant excitation. Here, we investigate how this coupling can be dynamically manipulated through charge-density control in a laterally patterned AlGaN/GaN heterostructure. The structure comprises metallic stripes separated by regions containing a two-dimensional electron gas (2DEG), forming a periodically modulated interface whose electromagnetic response is governed by the charge density between the stripes. In the unbiased state, the conductive 2DEG screens the incident terahertz field and suppresses excitation of guided modes. When the 2DEG is depleted, the change in boundary conditions allows efficient coupling into substrate resonances, producing a strong modulation at particular frequencies where extraordinary optical transmission (EOT) through the structure takes place. The results highlight the sensitive dependence of guided-mode-resonance mediated EOT on inter-stripe charge distribution and demonstrate a direct interplay between carrier dynamics and resonant electromagnetic phenomena in the terahertz regime.

Intensity-modulated proton therapy (IMPT) employs proton radiation rather than conventional x-rays to treat cancerous tumors. This approach offers significant advantages by minimizing the radiation exposure of surrounding healthy tissue, leading to improved patient outcomes and reduced side effects compared to traditional x-ray therapy. To ensure patient safety, each treatment plan must be experimentally validated before clinical implementation. However, current dosimetry devices face limitations in performing angled beam measurements and obtaining multi-depth assessments, both of which are essential for verifying IMPT treatment plans. In this study, the performance of a beta-Ga2O3-based metal-semiconductor-metal detector with a low-noise amplifier has been studied and evaluated under various proton radiation doses and energy levels delivered by a MEVION S250i proton accelerator. The detector's performance was also compared with that of an ionization chamber. The beta-Ga2O3 detector exhibited a linear response with proton dose for single-spot irradiations, and its response to varying proton energies closely matched both the ion chamber data and simulated dose distributions. These findings highlight the potential of beta-Ga2O3-based detectors as robust dosimetry devices for IMPT applications.

Rutile GeO2 (r-GeO2) is a promising ultrawide bandgap semiconductor; however, achieving controlled epitaxial films remains challenging due to competing phases and growth kinetics. In this work, we demonstrate orientation-dependent growth of GeO2 films on rutile TiO2 substrates with (100), (110), (001), and (111) orientations using metal–organic chemical vapor deposition (MOCVD). Among the investigated orientations, the (111) surface supports the formation of continuous, predominantly r-GeO2 films with comparatively reduced surface roughness, whereas the (001) orientation also enables rutile phase formation but with higher roughness, and the other orientations showed mixed phases and non-uniform morphologies. Reducing growth pressure improves crystalline quality, with the rocking curve full width at half maximum (FWHM) decreasing from 1.86° to 0.396° at 300 and 80 Torr, respectively. A direct comparison between continuous and seed-driven stepwise crystallization (SDSC) growth indicates that the segmented growth pathway assists rutile phase stabilization under the present MOCVD conditions, whereas continuous growth yields amorphous films. The resulting films exhibit continuous morphology with comparatively reduced roughness (∼23 nm) and remain stable after water treatment. Under the present high temperature X-ray diffraction conditions, amorphous films show no detectable crystallization up to 950°C, suggesting that crystallization is strongly influenced by growth-mediated conditions. These results offer guidelines for the controlled growth of (111)-oriented r-GeO2 films for ultrawide-bandgap semiconductor applications.

Rutile germanium dioxide (r-GeO2) has recently emerged as a promising ultrawide-bandgap (UWBG) semiconductor owing to its wide bandgap (similar to 4.4-5.1 eV), ambipolar doping potential, and high theoretical thermal conductivity. However, experimental data on the thermal conductivity of r-GeO2 epitaxial layers have not been reported, primarily due to challenges in phase control and surface roughness. Here, we report a high thermal conductivity of 52.9 +/- 6.6 W m(-1) K-1 for high-quality (002) r-GeO2 films grown by metal-organic chemical vapor deposition and characterized using time-domain thermoreflectance. The phase control was achieved through a seed-driven stepwise crystallization approach, and the surface roughness was significantly reduced from 76 to 16 nm (locally as low as 1 & Aring;) via chemical mechanical polishing. These results highlight the promise of r-GeO2 as a UWBG oxide platform for power electronics applications.

The thermal stability and structural evolution of a GaN high-electron mobility transistor (HEMT) heterostructure grown on a Si (111) substrate were investigated using in situ high-temperature x-ray diffraction, reciprocal space mapping (RSM), Raman spectroscopy, and rocking-curve (RC) analysis at varying temperatures. The heterostructure, consisting of a p-GaN cap, an AlGaN barrier, and a GaN channel supported by two AlGaN/AlGaN superlattice buffer layers, maintained clear and periodic satellite peaks up to a temperature of 1000 degrees C, confirming structural integrity. Symmetric and asymmetric RSM results reveal that both the Si and GaN diffraction peaks shift with increasing temperature, consistent with thermal expansion, and show no significant broadening or relaxation throughout the heating process. The c-lattice constant follows the theoretical expansion predicted by the multi-frequency Einstein model, whereas the a-lattice expansion is slower due to in-plane strain constraints imposed by the underlying Si substrate and buffer layers. Irreversible strain relaxation and thermal mismatch-induced stress redistribution induce a residual compressive strain of roughly 0.3% in the GaN channel after cooling, which has been further confirmed in Raman spectra through a blue shift (similar to 1 cm(-1)) of the GaN E-2 (high) phonon mode, corresponding to an in-plane strain of -0.15% +/- 0.16%. RC analysis revealed an increase in both screw and edge dislocation densities of 28% and 12%, respectively. These results collectively demonstrate that the GaN HEMT heterostructure exhibits robust crystalline stability up to 1000 degrees C without cracking due to strain relaxation, with only minor strain redistribution and limited dislocation activity, providing experimental evidence for GaN devices' applications under high-temperature conditions.

Intensity-modulated proton therapy (IMPT) is an advanced cancer treatment modality that offers advantages over conventional X-ray therapies, particularly in its ability to minimize radiation dose beyond the tumor target. This reduction in unnecessary irradiation exposure lowers the risk to surrounding healthy tissue and reduces side effects compared to conventional X-ray treatments. However, due to the high complexity of IMPT plans, each plan must be independently validated to ensure the safety of the radiation exposure to the patient. While ion chambers are currently used for this purpose, their limitations-particularly in angled beam measurements and multidepth assessments-hinder their effectiveness. Silicon-based detectors, commonly used in X-ray therapy, are unsuitable for IMPT due to their rapid degradation under proton irradiation. In this study, a beta -Ga2O3-based metal-semiconductor-metal detector was compared with a commercial ion chamber using a MEVION S250i proton accelerator. The beta -Ga2O3 detector demonstrated reliable detection of single-pulse proton doses as low as 0.26 MU and exhibited a linear charge-to-dose relationship across a wide range of irradiation conditions. Furthermore, its measurement variability was comparable to that of the ion chamber. These results highlight the strong potential of beta -Ga2O3 as a detector material for dose verification in IMPT.

Thermal stability and phase transformation of conductive alpha-(AlxGa1-x)(2)O-3/Ga2O3 heterostructure on sapphire substrates were investigated via in situ high temperature x-ray diffraction, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The conductive alpha-(AlxGa1-x)(2)O-3/Ga2O3 heterostructure with fluorine (F) doping was grown by mist-chemical vapor deposition on sapphire substrates, achieving a Hall mobility of 28 cm(2)/(V s). The heterostructure exhibited thermal stability up to similar to 550-575 degrees C before transforming to beta-(AlxGa1-x)(2)O-3/Ga2O3. The transformed beta-Ga2O3 is mainly polycrystalline rather than a high-quality epitaxial phase. Reciprocal space mapping results reveal that the edge dislocation density remains consistently higher than the screw dislocation density throughout the heating process, indicating that the crystalline imperfection in alpha-Ga2O3 is dominated by in-plane mosaicity. After the phase transformation from the alpha phase to the beta phase, catastrophic damage to the film and upheaval of the surface were observed by SEM and AFM.

Memory Phenomenon of GaN pn Junction by Engineering Its Interface, Which is Stable at High Temperatures up to 500oC

Thermal stability and phase transformation of conductive $α$-$(\mathrm{Al}_{0.16}\mathrm{Ga}_{0.84})_{2}\mathrm{O}_{3}/\mathrm{Ga}_{2}\mathrm{O}_{3}$ heterostructures on sapphire substrates were investigated using in situ high-temperature X-ray diffraction (HT-XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Conductive $α$-$(\mathrm{Al}_{0.16}\mathrm{Ga}_{0.84})_{2}\mathrm{O}_{3}/\mathrm{Ga}_{2}\mathrm{O}_{3}$ heterostructures with fluorine (F) doping were grown by mist chemical vapor deposition on sapphire substrates, achieving a Hall mobility of $28~\mathrm{cm^{2}\,V^{-1}\,s^{-1}}$ and an electron concentration of $1.4\times10^{20}~\mathrm{cm^{-3}}$. The heterostructures exhibited thermal stability up to approximately $550$--$

The crystallinity of β-Ga_2O_3 thin films grown by metal-organic chemical vapor deposition (MOCVD) is strongly influenced by reactor design and the resulting growth environment. In this work, we investigate the role of reactor height on the crystallinity evolution of MOCVD-grown β-Ga_2O_3 films by directly comparing long- and short-chamber showerhead configurations. Structural evolution was probed by in situ high-temperature X-ray diffraction (HT-XRD) as the MOCVD-grown films were heated from 25 ^∘C to 1100 ^∘C. Temperature-dependent XRD reveals a consistent redshift of the β-Ga_2O_3 (-201) reflection after HT-XRD heating and subsequent cooling to room temperature for both reactor geometries, indicating a similar thermally driven strain response. Quantitative rocking-curve analysis shows a non-monotonic temperature dependence of the (-201) full width at half maximum (FWHM), with minimum values of approximately 2.03^∘ and 2.72^∘ for the short- and long-chamber films, respectively, reflecting differences in mosaic alignment established during growth. Atomic force microscopy further shows that short-chamber-grown films exhibit smoother surfaces, with root-mean-square roughness values of approximately 7.7 nm before and 7.3 nm after HT-XRD heating, compared to 19.3 nm and 12.3 nm, respectively, for long-chamber-grown films. Overall, these results indicate that reactor height influences the initial crystalline and morphological templates of β-Ga_2O_3 films and modulates their elevated-temperature structural response, providing practical insights for optimizing MOCVD reactor design for high-quality β-Ga_2O_3 growth.

Rutile germanium dioxide (r-GeO2) is an ultrawide bandgap semiconductor with potential for ambipolar doping, making it a promising candidate for next-generation power electronics and optoelectronics. Growth of phase-pure r-GeO2 films by vapor phase techniques like metalorganic chemical vapor deposition (MOCVD) is challenging because of polymorphic competition from amorphous and quartz GeO2. Here, we introduce seed-driven stepwise crystallization (SDSC) as a segmented growth strategy for obtaining r-GeO2 films on r-TiO2 (001) substrate. SDSC divides the growth into repeated cycles of film deposition and cooling-heating ramps, which suppress the nonrutile phases. We demonstrate continuous, phase-pure, partially epitaxial r-GeO2 (001) films of thickness similar to 2 mu m exhibiting X-ray rocking curves with a full-width at half-maximum of similar to 597 arcsec. We discuss the underlying mechanisms of phase selection during SDSC growth. SDSC-based growth provides a generalizable pathway for selective vapor-phase growth of metastable or unstable phases, offering opportunities for phase-selective thin-film engineering.

Abstract Intensity-modulated proton therapy (IMPT) employs proton radiation rather than conventional x-rays to treat cancerous tumors. This approach offers significant advantages by minimizing the radiation exposure of surrounding healthy tissue, leading to improved patient outcomes and reduced side effects compared to traditional x-ray therapy. To ensure patient safety, each treatment plan must be experimentally validated before clinical implementation. However, current dosimetry devices face limitations in performing angled beam measurements and obtaining multi-depth assessments, both of which are essential for verifying IMPT treatment plans. In this study, the performance of a β -Ga 2 O 3 -based metal–semiconductor–metal detector with a low-noise amplifier has been studied and evaluated under various proton radiation doses and energy levels delivered by a MEVION S250i proton accelerator. The detector’s performance was also compared with that of an ionization chamber. The β -Ga 2 O 3 detector exhibited a linear response with proton dose for single-spot irradiations, and its response to varying proton energies closely matched both the ion chamber data and simulated dose distributions. These findings highlight the potential of β -Ga 2 O 3 -based detectors as robust dosimetry devices for IMPT applications.

NiO is a promising material for photovoltaics and high-power electronics, especially as a p-type material. However, the temperature limit of this material has not been thoroughly investigated. This work evaluates the structural evolution and thermal stability of NiO films using in situ high-temperature X-ray diffraction from 30 degrees C to 1100 degrees C in air. The film transformed from an amorphous state to a cubic NiO phase between 300 degrees C and 400 degrees C. The NiO (111) peak intensity follows a similar temperature-dependent trend as the film's resistivity, indicating that higher temperatures promote increased crystallinity, which correlates with higher resistivity. At 1100 degrees C, the formation of Ni2O3 was observed, accompanied by a transition to a highly resistive film. The study presents a clear evolution of NiO film quality and crystallinity across temperatures and establishes their correlation with the material's resistive behavior.

Rutile germanium dioxide (r-GeO2) has recently emerged as a promising ultrawide-bandgap (UWBG) semiconductor owing to its wide bandgap ( 4.4-5.1 eV), ambipolar doping potential, and high theoretical thermal conductivity. However, experimental data on the thermal conductivity of r-GeO2 epitaxial layers have not been reported, primarily due to challenges in phase control and surface roughness. Here, we report a high thermal conductivity of 52.9 +/- 6.6 W m^-1 K^-1 for high-quality (002) r-GeO2 films grown by metal-organic chemical vapor deposition (MOCVD) and characterized using time-domain thermoreflectance (TDTR). The phase control was achieved through a seed-driven stepwise crystallization (SDSC) approach, and the surface roughness was significantly reduced from 76 nm to 16 nm (locally as low as 1 A) via chemical mechanical polishing (CMP). These results highlight the promise of r-GeO2 as a UWBG oxide platform for power electronics applications.

NiO is a promising p-type material for photovoltaics and power electronics, but its temperature limits remain unclear. Using in situ high-temperature X-ray diffraction (HT-XRD) from 30 to 1100 C, we track the structural evolution of NiO thin films in air. The film crystallizes from an amorphous phase to cubic NiO between 300 and 400 C, where the emergence and growth of the (111) diffraction peak correlate with an increase in electrical resistivity. Further increases in temperature lead to improved crystallinity and higher resistivity. At 1100 C, the formation of Ni2O3 is observed, resulting in a highly resistive film. This study establishes a clear correlation between phase evolution, crystallinity, and resistive behavior in NiO thin films.

In this work, a guard array termination structure using hydrogen plasma technology (H-GAT) was proposed for multi-kV AlGaN/GaN heterojunction Schottky barrier diodes. A highest breakdown voltage (BV) of 9.5 kV, a specific on-resistance (R-ON) of 97 Slmm, and a capacitance at zero bias (C-j0) of 4.2 pF/mm were achieved on p-GaN/AlGaN/GaN-on-SiC platform. The fabrication process using hydrogen plasma termination was simple and easy to implement compared with other technologies used in multi-kV devices. This work provides an effective alternative route for the future development of lowcost, high-voltage 10 kV-class GaN power electronics.

We present the results of homojunction betagallium oxide (beta-Ga2O3) vertically conducting diodes grown by metal-organic chemical vapor deposition (MOCVD). The epitaxial layers of beta-Ga2O3 were of thickness similar to 0.5 um and were grown on n-doped 4-H silicon carbide (4H-SiC) substrate. To realize a diode structure, the initial growth layer on the substrate was doped with silicon with 5x10(17) cm(-3), then similar to 0.25 um layer was kept undoped. Three different samples were grown by changing the growth conditions; the sample one was grown by the traditional method by providing the continuous flow of growth precursors for gallium, oxygen, and silicon; in sample two, silicon was delta-doped in the doped part of the structure, and the sample three, the doped structure of the device was co-delta doped with silicon and indium. All other parameters, such as chamber pressure, growth temperature, and total gas flow rate, were kept constant. The samples were characterized by x-ray diffraction (XRD), Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS) prior to the processing. All three samples were processed to vertical conducting diodes of a diameter of 100 mu m. The sample's current-voltage (I-V) characteristics were measured and compared with each other and correlated with the growth process. All samples show significantly higher turn-on voltage due to high series resistance. Delta-doped samples showed lower turn-on voltages and large forward currents compared to the traditionally grown device structure. The results lead to a better growth process for beta-Ga2O3-based devices.