Hideo ISSHIKI (一色 秀夫)

This study investigates the effects of different fabrication and annealing atmospheres on the properties of samarium (Sm)‐doped titanium dioxide (TiO₂:Sm) thin films, with a focus on luminescence and electrical conductivity. TiO₂:Sm thin films are deposited by laser ablation and annealed at 700 °C in O₂ and H₂ + N₂ atmospheres. X‐ray diffraction analysis shows that fabrication and annealing in the H₂ + N₂ atmosphere significantly inhibit crystal growth. PL spectra reveal that films fabricated and annealed in O₂ exhibit the strongest luminescence, while those in the H₂ + N₂ show quenched luminescence. X‐ray absorption fine structure results indicate that Sm³⁺ ions in the non‐luminescent samples have a high‐symmetry oxygen coordination, which is unfavorable for luminescence. C–V and I–V measurements reveal a substantial increase in electrical conductivity for films fabricated and annealed in H₂ + N₂, attributed to the incorporation of hydrogen and the formation of oxygen vacancies. This study concludes that while the fabrication and annealing in the H₂ + N₂ atmospheres enhance the electrical conductivity of TiO₂:Sm thin films, they also degrade luminescence. Balancing luminescence intensity and electrical conductivity is crucial for the optical device application of TiO₂:Sm thin films. It is necessary to carefully adjust the fabrication and annealing conditions to enhance electrical conductivity while maintaining strong luminescence.

Abstract

Sm-doped TiO₂ thin films were synthesized by pulsed laser deposition. The luminescence and donor-generation properties of thin films annealed at various temperatures were investigated. The results showed that Sm-related emissions occurred in the temperature range 500 °C–800 °C. The donor densities in this temperature range were two orders of magnitude higher than that of the undoped TiO₂ thin film. The effect of annealing within the temperature window indicates a local fine structural transition of the ligands around Sm³⁺ ions from T_d symmetry to the lower C_4v one; these ions are effective luminescence centers in TiO₂:Sm thin films. This local structural distortion also increases defect generation, and this increases the donor density in the same temperature region.

Abstract

A CuAlO₂ (CAO) bottom gate top contact p-type thin film transistor (TFT) is demonstrated. The CAO thin film is synthesized through a digitally processed DC sputtering (DPDS) technique, employing a precise layer-by-layer (LBL) deposition strategy. X-ray diffraction analysis exhibited distinct peaks beyond 600 °C. The CAO film shows a dominant phase along the (004) plane at the elevated temperature of 990 °C. The fabricated CAO p-TFT exhibits field effect mobility of 4.1 cm² V⁻¹ s⁻¹. In addition, the p-TFT characteristics were observed even in the as-deposited CAO film. The DPDS-assisted LBL approach offers a promising pathway for controlled stacking deposition routes in the growth of CAO thin films, enabling enhanced performance and device integration.

We have developed a digitally processed DC reactive sputtering (DPDRS) system that enables synthesis of arbitrarily designed atomically
precise deposition of metal oxide compounds. Pulsed-DC sputtering employing a digital pulse pattern generator can perform the temporally
alternating process of multiple metal sputtering and oxidation. High-speed switching of the pulsed-DC sputtering process driven by the
digital signal processing was confirmed from time-resolved plasma emission spectroscopy. Metal sputtering, which was temporally separated
from the oxidation process, resulted in a deposition rate higher than 1 μm/h. The DPDRS was applied to layer-by-layer synthesis of
(Er0.1Y0.9)2SiO5 (EYSO) films oriented to the ⟨100⟩ direction.
X-ray diffraction measurements indicated a formation of ⟨100⟩ highly oriented (Er0.1Y0.9)2SiO5 crystalline thin films. Photoluminescence
spectra and the decay characteristics also showed synthesis of high crystalline quality EYSO films better than those obtained by pulsed laser
deposition.