Hyoung-Seuk Choi

Density of state effective mass and related charge transport properties in K-doped BiCuOSe

We report the enhanced p-type conduction properties in BiCuOSe by doping of monovalent ions (K+). As compared with undoped BiCuOSe, simultaneous increase in both the carrier concentration and the Hall mobility was achieved in the K-doped BiCuOSe. The origin of the enhancement was discussed in terms of the two-band structure in the valence band of the BiCuOSe, and the density of state effective masses of the heavy (∼1.1 me) and light hole (∼0.18 me) were estimated by using Pisarenko relation.

Point defect-assisted doping mechanism and related thermoelectric transport properties in Pb-doped BiCuOTe

In this article we report point defect-assisted doping mechanism and related thermoelectric transport properties in Pb-doped BiCuOTe compounds. The substitution of trivalent Bi3+ with divalent Pb2+ led to the generation of more than one hole per single Pb atom. The origin of the extra charge carrier was discussed in terms of the formation energy of p-type native point defects, and it could be evidenced by the density functional theory calculations. Related charge transport properties indicated that control of the native point defect is critical to achieve high thermoelectric performance in BiCuOTe material system.

Effects of SiO2 interlayer on electrical properties of Al-doped ZnO films under bending stress

We report the effects of an SiO2 interlayer on the structural and electrical properties of Al-doped ZnO (AZO) films grown on polyimide (PI) substrate. By inserting a SiO2 interlayer between the AZO film and the PI substrate, we could control the microstructure of the AZO films. The granule size of the SiO2 interlayer was determined strate temperature, and the column width in the AZO film was strongly affected by the initial granule size in the interlayer. In-situ Hall measurement of the AZO films under bending stress was performed for the first time, and flexibility-related electrical properties of the AZO films were discussed.

Life and failure mechanism prediction of eco-friendly P2O5-SnO2-B2O3 glass frits

Glass frits are used widely in the VFD, PDP, LCD, and OLED displays, solar cells, and automobiles. It is essential for glass frits to exhibit material properties such as low melting temperatures and coefficient of thermal expansion close to glass to prevent thermal shock and to lower the thermal stress. Glass frit containing 60%–85% of PbO lowers the melting temperature. However, PbO causes environmental pollution. In this study, we developed P2O5-SnO2-B2O3 glass frits and carried out life tests on these systems. In addition, life tests were also carried out on Pb-containing glass frits (VFD) for comparison to predict the life of the P2O5-SnO2-B2O3 systems. Subsequently, the failure mechanisms of VFD and Pb-free P2O5-SnO2-B2O3 glass frits were analyzed.