• Journal of the Korean Ceramic Society
• /
• v.40 no.8
• /
• pp.725-729
• /
• 2003

The fluorine doping along with heavy metal oxides remarkably raised the $^3$H$_4$ lifetime and the quantum efficiency in Tm$^{3+}$-doped silicate glasses. 29 mol% of fluorine substitution for oxygen in 70SiO$_2$-15Pbo-12ZnO-3KO$_{1}$2/ glass raised $^3$H$_4$ lifetime to 193 $mutextrm{s}$. Refractive indices were raised by heavy metal oxide substitution, but hardly changed by fluorine substitution. The fluorine doping changed the local structure around Tm$^{3+}$ions, then low energy vibrations related to fluorine are considered to largely reduce the multi-phonon relaxation rates in the oxyfluoride silicate glasses. The $^3$H$_4$ lifetimes and absorption and emission spectra of Tm$^{3+}$doped silicate and oxyfluoride silicate glasses are reported, and Judd-Ofelt calculation results are discussed in this paper.

• Journal of the Korean Vacuum Society
• /
• v.19 no.5
• /
• pp.391-396
• /
• 2010

The pn junction for solar cell was prepared on p-type Si wafer by the furnace using the $POCl_3$ and oxygen mixed precursor to research the characteristic of interface at pn junction. The sheet resistance was decreased in accordance with the increasing the diffusion process time for n-type doping on p-type Si wafer. The electron affinity at the interface in the pn junction was decreased with increasing the amount of n-type doping and the sheet resistance also decreased. Consequently, the drift current due to the generation of EHP increased because of low potential barrier. The efficiency and fill factor were increased at the solar cell with increasing the diffusion process time.

• Current Photovoltaic Research
• /
• v.5 no.4
• /
• pp.113-121
• /
• 2017

The researches on the silicon-based thin films are being actively carried out. The silicon-based thin films can be made as amorphous, microcrystalline and mixed phase and it is known that the optical bandgap can be controlled accordingly. They are suitable materials for the fabrication of single junction, tandem and triple junction solar cells. It can be used as a doping layer through the bonding of boron and phosphorus. The carbon and oxygen can bond with silicon to form a wide range of optical gap. Also, The optical gap of hydrogenated amorphous silicon germanium can be lower than that of silicon. By controlling the optical gaps, it is possible to fabricate multi-junction thin film silicon solar cells with high efficiencies which can be promising photovoltaic devices.

• Journal of Korean Vacuum Science & Technology
• /
• v.2 no.2
• /
• pp.78-84
• /
• 1998

ZnO:Al films were prepared by an rf magnetron sputtering and targets for the experiments were fabricated by sintering the mixture of ZnO and Al2O3. The most conductive film was obtained from the target with 2.0∼2.2 wt.% of Al2O3. Optical properties studied with spectroscopic ellipsometry showed band gap widening, i.e., the Burstein-Moss shift, with aluminum doping as well as with the elevation of deposition temperature. And it is found that the optical and electrical properties were related to the density of states as well as the variation of donor level. when hydrogen atoms were introduced into the films, the activation energy for the generation of oxygen vacancy was smaller for the films showing higher conductivity. This indicates that the optimum deposition condition for highly conductive ZnO:Al film has strong relation to the optimum doping condition.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.8 no.3
• /
• pp.401-406
• /
• 1998

For the applications in optical waveguides and devices, LiNbO_3$ single crystals need to overcome the weakness of optical damage due to the inhomogeneities of laser-induced refractive index. This problem can be solved by doping of Mg in LiNbO_3$ and proton exchange of LiNbO_3$. In this study, to understand the mechanism of optical damage resistance in LiNbO_3$, the changes of lattice defects in LiNbO_3$ caused by MgO doping and acid treatment were observed indirectly by $OH^-$ absorption bands using a FT-IR spectrophotometer. The effect of lattice defects on temperature, heat-treatment and polishing were also investigated. It is shown that MgO doping increases optical damage resistance by generating the defects of $Mg_{Nb}^{2+}$ in the lattice of LiNbO_3$, and that proton exchange by implantation of $H^+$ ion in the hexagonally closest packed oxygen layers on the surface of LiNbO_3$, makes lattice defects, which diffuse into the crystal after heat-treatment above $400^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.23 no.11
• /
• pp.854-858
• /
• 2010

In this study, we have investigated the effects of Cr dopant on the sintering and electrical properties of ZnO-$Sb_2O_3$ (ZS) ceramics for varistor application. Spinel phases including $\alpha-$ and $\beta$-type was formed at ZS system and $\alpha$-spinel was stabilized by Cr doping in ZS system. Densification of ZS and ZSCr system was retarded to $1000^{\circ}C$ by the formation of spinel at $800^{\circ}C$. The morphology and its distribution of spinel phases in ZS system was homogeneous but disturbed by Cr doping. In ZSCr the densification of ZnO compared with ZS system was more retarded by low concentration of Zn interstitial defects induced by Cr doping in addition to the effect of spinel phase formation. The defects in each system were identified as attractive coulombic center (ZS: 0.13 eV, ZSCr: 0.12 eV) and singly charged oxygen vacancy $V_0^{\cdot}$ (ZSCr: 0.33 eV). In all ZS and ZSCr system have week varistor behavior by the formation of double Schottky barrier at grain boundary but its stability of barrier was very sensitive to sintering temperature.

• Korean Journal of Materials Research
• /
• v.5 no.1
• /
• pp.36-41
• /
• 1995

Dielectric properties were investigated at Mn doped $(Pb_{1-x}Ca_{x})ZrO_{3}$ with x=0.38 in microwavefrequencies. Both the density and Q values of sintered ceramics increased with increasing calciningtemperature. In the sample sintered at $1300^{\circ}C$ for 2 hrs, the deped Mn ions completely solubled in $(Pb,Ca)ZrO_{3}$ phase until 0.5wt% and the grain size was independent of doping amount. It was observed thathigh dielectric constant of 90 - 100 and high quality factor of 1300 at 4 GHz for O.l5wt% Mn doped$(Pb_{0.62}Ca_{0.38})ZrO_{3}$. The Mn" and Mn" worked as acceptors in $(Pb,Ca)ZrO_{3}$ which created the oxygen vacancies and affected the increment of the Q values. However, the excess Mn doping more than 0.5wt% resulted in decreasing Q values.decreasing Q values.

• Journal of the Korean Ceramic Society
• /
• v.34 no.8
• /
• pp.803-810
• /
• 1997

Ba0.5Sr0.5TiO3 thin films were deposited by RF magnetron sputliring method in order to clarify the anneal condition and doping effect on loakage current Nb and Al were selected as electron donor and acceptor dopants respectively, in the BST films because they have been known to have nearly same ionic radii as Ti and thought to substitute Ti sites to influence the charge carrier and the acceptor state adjacent to the gram boundary. BST thin films prepared in-situ at elevated temperature showed selatively high leakage current density and low breakdown voltage. In order to achieve smooth surface and to improve electrical properties, BST thin films were deposited at room temperature and annealed at elevated temperature. Post-annealed BST thin films showed smoother surface morphology and lower leakage current density than in-situ prepared thin films. The leakage current density of Al doped thin films was measured to be around 10-8A/cm2, which is much lower than those of undoped and Nb doped BST films. The result clearly demonstrates that higher Schottky barrier and lower mobile charge carrier concentration achieved by annealing in the oxygen atmosphere and by Al doping are desirable for reducing leakage current density in BST thin films.

• Composites Research
• /
• v.36 no.5
• /
• pp.342-348
• /
• 2023

There has been increasing demand for real-time monitoring of body and ambient temperatures using wearable devices. Graphene-based thermistors have been developed for high-performance flexible temperature sensors. In this study, the temperature coefficient of resistance (TCR) of monolayer graphene was controlled by coating polyethylenimine (PEI) on graphene surfaces to enhance its temperature-sensing performances. Monolayer graphene grown by chemical vapor deposition (CVD) was wet-transferred onto a target substrate. To facilitate the interfacial doping by PEI, the hydrophobic graphene surface was altered to be hydrophilic by oxygen plasma treatments while minimizing defect generation. The effect of PEI doping on graphene was confirmed using a back-gated field-effect transistor (FET). The CVD-grown monolayer graphene coated with PEI exhibited an improved TCR of -0.49(±0.03) %/K in a temperature range of 30~50℃.

• Journal of the Microelectronics and Packaging Society
• /
• v.30 no.3
• /
• pp.94-101
• /
• 2023

Zinc oxide(ZnO) is a semiconductor material with a bandgap of 3.37 eV and an exciton binding energy of 60 meV for various applications. Recently ZnO has been proven to enhance its electrical properties for utilization as an alternative for transparent conducting oxide (TCO) materials. In this study, cation(Al, Ga)-anion(F) single and double doped ZnO thin films were grown by atomic layer deposition (ALD) to enhance the electrical properties. The structural and optical properties of doped ZnO thin films were analyzed, and doping effects were confirmed to electrical characteristics. In single doped ZnO, it was observed that the carrier concentration was increased after doping, acting as a donor to ZnO. Among the single doping elements, F doped ZnO(FZO) showed the highest mobility and conductivity due to the passivation effect of oxygen vacancies. In the case of double doping, higher electrical characteristics were observed compared to single doping. Among the samples, Al-F doped ZnO(AFZO) exhibited the lowest resistance value. This results can be attributed to an increase in delocalized electron states and a decrease in lattice distortion resulting from the differences in ionic radius. The partial density of states(PDOS) was also analyzed and observed to be consistent with the experimental results.