F-doped α-Ga2O3 thin films with low electrical resistivity were epitaxially grown on c-plane α-Al2O3 substrates by means of mist chemical vapor deposition. The resistivity of the α-Ga2O3 thin films ...was decreased dramatically by incorporating F into α-Ga2O3, achieving a minimum resistivity of 6.2 × 10−2 Ω·cm in a 1050 nm thick film grown from a precursor solution with a F/Ga ratio of 20%. Further, the carrier concentration was 1.3 × 1019 cm−3, and the Hall mobility was 4.6 cm2/Vs with the F/Ga ratio of 20% and a film thickness of 1560 nm. Secondary ion mass spectrometry revealed that the F concentration incorporated into the α-Ga2O3 thin film was approximately 1 × 1020 cm−3, and the activation ratio was approximately 10%. The higher F/Ga ratio in the precursor solution caused lower crystallinity, as demonstrated by X-ray diffraction rocking curves. For all F/Ga ratios, as the film thickness increased to approximately 1000 nm, the electrical resistivity of the thin films drastically decreased. In the thinner films, the dislocations at the interface between the α-Ga2O3 thin films and the α-Al2O3 substrates are thought to trap electrons and compensate the free carriers or deteriorate the mobility.
•F doped α-Ga2O3 thin films with low electrical resistivity were grown on α-Al2O3 substrate.•The dependence the electrical resistivity on the F ratio and the film thickness was investigated.•The activation ratio of F was revealed by Hall measurement and SIMS.
•Corundum structured a-, m-, and r-plane α-Ga2O3 were grown on rh-ITO via mist CVD.•α-Fe2O3 buffer layers on rh-ITO facilitated preferential growth of α-Ga2O3.•XRD analyses revealed that α-Ga2O3 thin ...films were epitaxially grown.•Surface morphologies of α-Ga2O3 differed depending on the crystal orientation.
α-Ga2O3 has garnered significant attention as a promising next-generation material for applications in power-switching and deep ultraviolet optoelectronics owing to its ultrawide bandgap. However, fabricating α-Ga2O3-based devices with a vertical structure is challenging because α-Ga2O3 requires heteroepitaxial growth on a heterogeneous substrate, typically insulating sapphire. In this study, we investigated the heteroepitaxial growth of a-, m-, and r-plane α-Ga2O3 on rhombohedral indium tin oxide (rh-ITO) electrodes via mist chemical vapor deposition. X-ray diffraction (XRD) 2θ-ω and φ scan analyses revealed that a-, m-, and r-plane α-Ga2O3 epitaxial thin films were successfully grown on rh-ITO bottom electrodes when α-Fe2O3 buffer layers were inserted. No phase separation or in-plane rotation was observed in the XRD results of the α-Ga2O3 thin films. The α-Fe2O3 buffer layers facilitated the preferential growth of α-Ga2O3 on various planes of rh-ITO. The surface morphology of the a-, m-, and r-plane α-Ga2O3, examined via field emission scanning electron microscopy, differed depending on the crystal plane. The results obtained in this study have potential applications in the development of vertical-structured devices with α-Ga2O3 thin films.
In the 3 GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex, significant losses were observed at the branching of the H0 dump line and the beam position monitor that was ...inserted downstream of the H0 dump branch duct. These losses were caused by the large-angle scattering of the injection and circulating beams at the charge-exchange foil. To realize high-power operation, these losses must be mitigated. Therefore, a new collimation system was developed and installed in October 2011. To efficiently optimize this system, the behavior of particles scattered by the foil and produced by the absorber were simulated, and the optimal position and angle of the absorber were investigated. During this process, an angle regulation method for the absorber was devised. An outline of this system, the angle regulation method for the absorber, and the performance of this new collimation system are described.
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