Aeran Song

Improvement of device performance and instability of tungsten-doped InZnO thin-film transistor with respect to doping concentration

W-doped InZnO (WIZO) thin-film transistors (TFTs) were fabricated by co-sputtering with different W doping concentrations. We varied the W doping concentration to change the device performance and stability of the WIZO TFTs. WIZO TFTs with a W doping concentration of ~1.1% showed the lowest threshold voltage shift and hysteresis. We correlated the device characteristics with the evolution of the electronic structure, such as band alignment, chemical bonding states, and band edge states. As the W doping concentration increased, the oxygen-deficient bonding states and W suboxidation states decreased, while the conduction-band offset and the incorporation of the WO x electronic structure into the conduction band increased.

Enhancement of the Device Performance and the Stability with a Homojunction-structured Tungsten Indium Zinc Oxide Thin Film Transistor

Tungsten-indium-zinc-oxide thin-film transistors (WIZO-TFTs) were fabricated using a radio frequency (RF) co-sputtering system with two types of source/drain (S/D)-electrode material of conducting WIZO (homojunction structure) and the indium-tin oxide (ITO) (heterojunction structure) on the same WIZO active-channel layer. The electrical properties of the WIZO layers used in the S/D electrode and the active-channel layer were adjusted through oxygen partial pressure during the deposition process. To explain enhancements of the device performance and stability of the homojunction-structured WIZO-TFT, a systematic investigation of correlation between device performance and physical properties at the interface between the active layer and the S/D electrodes such as the contact resistance, surface/interfacial roughness, interfacial-trap density, and interfacial energy-level alignments was conducted. The homojunction-structured WIZO-TFT exhibited a lower contact resistance, smaller interfacial-trap density, and flatter interfacial roughness than the WIZO-TFT with the heterojunction structure. The 0.09 eV electron barrier of the homojunction-structured WIZO-TFT is lower than the 0.21 eV value that was obtained for the heterojunction-structured WIZO-TFT. This reduced electron barrier may be attributed to enhancements of device performance and stability, that are related to the carrier transport.

Characterization of Rotational Stacking Layers in Large-Area MoSe2 Film Grown by Molecular Beam Epitaxy and Interaction with Photon

Transition metal dichalcogenides (TMDCs) are promising next-generation materials for optoelectronic devices because, at subnanometer thicknesses, they have a transparency, flexibility, and band gap in the near-infrared to visible light range. In this study, we examined continuous, large-area MoSe2 film, grown by molecular beam epitaxy on an amorphous SiO2/Si substrate, which facilitated direct device fabrication without exfoliation. Spectroscopic measurements were implemented to verify the formation of a homogeneous MoSe2 film by performing mapping on the micrometer scale and measurements at multiple positions. The crystalline structure of the film showed hexagonal (2H) rotationally stacked layers. The local strain at the grain boundaries was mapped using a geometric phase analysis, which showed a higher strain for a 30° twist angle compared to a 13° angle. Furthermore, the photon-matter interaction for the rotational stacking structures was investigated as a function of the number of layers using spectroscopic ellipsometry. The optical band gap for the grown MoSe2 was in the near-infrared range, 1.24-1.39 eV. As the film thickness increased, the band gap energy decreased. The atomically controlled thin MoSe2 showed promise for application to nanoelectronics, photodetectors, light emitting diodes, and valleytronics.

Enhancing the performance of tungsten doped InZnO thin film transistors via sequential ambient annealing

This study suggests a sequential ambient annealing process as an excellent post-treatment method to enhance the device performance and stability of W (tungsten) doped InZnO thin film transistors (WIZO-TFTs). Sequential ambient annealing at 250 °C significantly enhanced the device performance and stability of WIZO-TFTs, compared with other post-treatment methods, such as air ambient annealing and vacuum ambient annealing at 250 °C. To understand the enhanced device performance and stability of WIZO-TFT with sequential ambient annealing, we investigate the correlations between device performance and stability and electronic structures, such as band alignment, a feature of the conduction band, and band edge states below the conduction band. The enhanced performance of WIZO-TFTs with sequential ambient annealing is related to the modification of the electronic structure. In addition, the dominant mechanism responsible for the enhanced device performance and stability of WIZO-TFTs is considered to be a change ...

Modulation of the electrical properties in amorphous indium-gallium zinc-oxide semiconductor films using hydrogen incorporation

The electrical properties of amorphous-indium-gallium-zinc-oxide (a-IGZO) thin films were investigated after thermal annealing and plasma treatment under different gas conditions. The electrical resistivity of a-IGZO thin films post-treated in a hydrogen ambient were lower than those without treatment and those annealed in air, regardless of the methods used for both thermal annealing and plasma treatment. The electrical properties can be explained by the quantity of hydrogen incorporated into the samples and the changes in the electronic structure in terms of the chemical bonding states, the distribution of the near-conduction-band unoccupied states, and the band alignment. As a result, the carrier concentrations of the hydrogen treated a-IGZO thin films increased, while the mobility decreased, due to the increase in the oxygen vacancies from the occurrence of unoccupied states in both shallow and deep levels.

Unraveling the Issue of Ag Migration in Printable Source/Drain Electrodes Compatible with Versatile Solution-Processed Oxide Semiconductors for Printed Thin-Film Transistor Applications

In recent decades, solution-processable, printable oxide thin-film transistors have garnered a tremendous amount of attention given their potential for use in low-cost, large-area electronics. However, printable metallic source/drain electrodes undergo undesirable electrical/thermal migration at an interfacial stack of the oxide semiconductor and metal electrode. In this study, we report oleic acid-capped Ag nanoparticles that effectively suppress the significant Ag migration and facilitate high field-effect mobilities in oxide transistors. The origin of the role of surface-capped Ag nanoparticles is clarified with comparative studies based on X-ray photoelectron spectroscopy and X-ray absorption spectroscopy.

Enhanced efficiency in lead-free bismuth iodide with post treatment based on a hole-conductor-free perovskite solar cell

Despite the excellent merits of lead perovskite solar cells, their instability and toxicity still present a bottleneck for practical applications. Bismuth perovskite has emerged as a candidate for photovoltaic (PV) applications, because it not only has a low toxicity but is also stable in air. However, the power conversion efficiency (PCE) remains an unsolved problem. We performed band gap tuning experiments to improve the efficiency. The absorption of ABi3I10 structure films was extended within the visible region, and the optical band gap was decreased considerably compared to that for Cs3Bi2I9. Furthermore, we explained the correlation between the structure and the optical properties via a first-principles study. A device employing CsBi3I10 as a photoactive layer exhibits a PCE of 1.51% and an excellent ambient stability over 30 days.

Effects of Embedded TiO2−x Nanoparticles on Triboelectric Nanogenerator Performance

Triboelectric nanogenerators (TENGs) are used as self-power sources for various types of devices by converting external waves, wind, or other mechanical energies into electric power. However, obtaining a high-output performance is still of major concern for many applications. In this study, to enhance the output performance of polydimethylsiloxane (PDMS)-based TENGs, highly dielectric TiO2−x nanoparticles (NPs) were embedded as a function of weight ratio. TiO2−x NPs embedded in PDMS at 5% showed the highest output voltage and current. The improved output performance at 5% is strongly related to the change of oxygen vacancies on the PDMS surface, as well as the increased dielectric constant. Specifically, oxygen vacancies in the oxide nanoparticles are electrically positive charges, which is an important factor that can contribute to the exchange and trapping of electrons when driving a TENG. However, in TiO2−x NPs containing over 5%, the output performance was significantly degraded because of the increased leakage characteristics of the PDMS layer due to TiO2−x NPs aggregation, which formed an electron path.