Hokkaido University · Materials Science
Professor Hai Jun Cho's research lab specializes in the development and fundamental understanding of advanced oxide semiconductors and functional oxides, with a focus on transparent conducting oxides, transparent electronics, and thermoelectric materials. The lab investigates epitaxial film growth, defect engineering, and carrier transport mechanisms to enhance electronic and thermal properties in complex oxide heterostructures. Key research directions include optimizing wide bandgap oxide semiconductors like La-doped BaSnO₃ and SrSnO₃ for optoelectronic and deep-UV applications, as well as exploring anisotropic thermal conductivity in layered oxides for thermal management. The lab employs advanced pulsed laser deposition and post-growth annealing techniques to control stoichiometry and defect structures at the atomic level.
Figures are computed from collected data and may differ slightly.
Wide bandgap (Eg ∼ 3.1 eV) La-doped BaSnO3 (LBSO) has attracted increasing attention as one of the transparent oxide semiconductors since its bulk single crystal shows a high carrier mobility (∼320 cm2 V−1 s−1) with a high carrier concentration (∼1020 cm−3). For this reason, many researchers have fabricated LBSO epitaxial films thus far, but the obtainable carrier mobility is substantially low compared to that of single crystals due to the formation of the lattice/structural defects. Here we rep
La-doped SrSnO3 (LSSO) is known as one of the deep-ultraviolet (DUV)-transparent conducting oxides with an energy bandgap of similar to 4.6 eV. Since LSSO can be grown heteroepitaxially on more wide bandgap substrates such as MgO (E-g similar to 7.8 eV), LSSO is considered to be a good candidate for a DUV-transparent electrode. However, the electrical conductivity of LSSO films is below 1000 S cm(-1), most likely due to the low solubility of the La ion in the LSSO lattice. Here, we report that h
Abstract Layered cobalt oxides, A x CoO 2 (A = Li, Na, Ca, and Sr), are attracting attention as thermoelectric materials showing large thermoelectric figure of merit ZT = S 2 σTκ −1 ( S : thermopower, σ: electrical conductivity, T : absolute temperature, κ: thermal conductivity) at higher temperatures. Due to the layered structure, A x CoO 2 shows strong anisotropy in the thermoelectric properties; both S and σ are large along the layer though systematic study in κ is not reported thus far. Here
Transparent La-doped BaSnO${}_{3}$ (LBSO) is a promising optoelectronic material due to its excellent single-crystal electron transport properties. However, the mobility of LBSO thin films is much lower than single-crystal values. This is mainly attributed to threading dislocations, but they have not been enough to fully explain this phenomenon. Using transport properties and stoichiometry control, the authors investigate the mobility suppression in LBSO films in a broader perspective. The resul
Abstract Heat conduction in ceramics is attributed to phonon propagation, which can be strongly suppressed at boundaries. Usually, polycrystals show lower thermal conductivity (κ) than single crystals, as polycrystals contain many grain boundaries. For functional applications in thermal management technologies, ceramics with low thermal conductivity are required. While grain boundary engineering is effective for reducing κ, its utilization is limited by the fact that other functional properties
Wide bandgap (~3.1 eV) La-doped BaSnO3 (LBSO) has attracted increasing attention as one of the transparent oxide semiconductors since its bulk single crystal shows a high carrier mobility (~320 cm2 V-1 s-1) with a high carrier concentration (~10^20 cm-3). For this reason, many researchers have fabricated LBSO epitaxial films thus far, but the obtainable carrier mobility is substantially low compared to that of single crystals due to the formation of the lattice/structural defects. Here we report
Abstract Thin film transistors (TFT) with deep‐UV transparency are a promising component for next‐generation optoelectronics such as biosensors. Among several deep‐UV transparent oxide semiconductors, SrSnO 3 is an excellent candidate material owing to its wide band gap (≈4.6 eV) and rather high carrier electron mobility. Herein, fabrication and operation mechanism of the SrSnO 3 ‐TFT is shown. A metal–insulator‐semiconductor structure is fabricated on a 28 nm‐thick SrSnO 3 film. The resultant T
Abstract The interface between two materials can be expected to show exotic optical, electrical, and thermal transport properties due to the difference in chemical bonding and chemical potential. However, in conventional material systems, the volume fraction of the interface is small compared to bulk, and interfacial properties are thus difficult to utilize. In this regard, multilayered films are essential to increase the volume fraction of interfaces and functionalize their properties. Here it
La-doped SrSnO3 (LSSO) is known as one of the deep-ultraviolet (DUV)-transparent conducting oxides with an energy bandgap of ∼4.6 eV. Since LSSO can be grown heteroepitaxially on more wide bandgap substrates such as MgO (Eg ∼ 7.8 eV), LSSO is considered to be a good candidate for a DUV-transparent electrode. However, the electrical conductivity of LSSO films is below 1000 S cm−1, most likely due to the low solubility of the La ion in the LSSO lattice. Here, we report that high electrically condu
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