Yeong-Cheol Kim

Investigation of zinc interstitial ions as the origin of anomalous stress-induced hump in amorphous indium gallium zinc oxide thin film transistors

In this paper, we investigated an anomalous hump in the bottom gate staggered amorphous indium-gallium zinc oxide thin-film transistors. During the positive gate bias stress, a positive threshold voltage shift is observed in transfer curve and an anomalous hump occurs as the stress time increases. The hump becomes more serious as the gate bias stress increases while it is not observed under the negative bias stress. From the simulation of a long range migration of zinc interstitial ions (Zni) and the measurement of the diode characteristics after the constant positive bias stress, the origin of the hump can be explained by the migration of the positively charged mobile Zni during the constant positive gate bias stress, which can be conformed by increasing the concentration of Zni from the result of the Auger ZnL3M4.5M4.5 spectra.

Y-doped BaZrO₃에서의 산소 공공과 프로톤의 이동

We studied the transfer of oxygen vacancy and proton in Y-doped BaZrO₃(BYZ) using density functional theory (DFT). An oxygen vacancy was generated in the 2×2×2 BYZ superstructure by replacing two Zr atoms with two Y atoms to satisfy the charge neutrality condition. The O vacancy transfer between the first and second nearest O atom sites from a Y atom showed the lowest activation energy barrier of 0.42 eV, compared to the other transfers between first and first, and second and second in the superstructure. Two protons were inserted in the structure by adding a proton and hydroxyl that were supplied by the dissociation of a water molecule. The two protons bonded to the first and second nearest O atoms were energetically the most favorable. The activation energy barrier for a proton transfer in the structure was 0.51 eV, when either proton transferred to its neighbor O atom. This value was well matched with the experimentally determined one.

BaZrO₃의 부피 변화가 프로톤 전도 에너지 장벽에 미치는 영향

We studied the energy barrier for proton conduction with volume variation in BaZrO₃ using a first principles study to investigate an optimum volume for the proton conduction. The volume increase of BaZrO₃ was expected to decrease the energy barrier for proton rotation and to increase that for proton transfer, and these trends could be extrapolated when the volume was decreased. However, the energy barriers for the proton transfer with the volume decrease were increased, while all the other energy barriers varied as expected. We could explain this unexpected behavior by the bent Zr?O?Zr structure, when the volume was decreased.

Effect of amino ligand size of Si precursors on initial reaction with an –OH-terminated Si(001) surface for atomic layer deposition

The effect of the amino ligand size of Si precursors on the initial reaction with an –OH-terminated Si(001) surface was investigated on the basis of the density functional theory for atomic layer deposition (ALD). The following six Si precursors were chosen in order of increasing ligand size to compare their initial reactions on the surface: dimethylaminosilane (SiH3[N(CH3)2], DMAS), ethylmethylaminosilane (SiH3[N(CH3C2H5)], EMAS), diethylaminosilane (SiH3[N(C2H5)2], DEAS), ethylisopropylaminosilane (SiH3[N(C2H5C3H7)], EIPAS), diisopropylaminosilane (SiH3[N(C3H7)2], DIPAS), and dipropylaminosilane (SiH3[N(C3H7)2], DPAS). The adsorption energies of the precursors and reaction energy barriers, and the desorption energies of the by-products were compared as a function of ligand size to evaluate the processing temperature range for ALD. DIPAS showed the widest temperature range for ALD among the six Si precursors.

Effect of Copper Oxide on Migration and Interaction of Protons in Barium Zirconate

The effect of copper oxide on migration and interaction of protons in barium zirconate was investigated using density functional theory. One copper atom was substituted for a zirconium atom site, and a proton was added to a 3×3×3 barium zirconate superstructure. An energy barrier of 0.89 eV for proton migration was the highest among several energy barriers. To investigate the interaction between multiple protons and a copper atom, two protons were added to the superstructure. Various proton positions were determined by the interaction between the two protons and the copper atom.

Effects of cobalt silicidation and postannealing on void defects at the sidewall spacer edge of metal–oxide–silicon field-effect transistors

The void formation at the edge of the sidewall spacer during postannealing is favorable in reducing both the number of excess silicon vacancies generated in the silicon substrate during silicidation, and the tensile stress concentrated at the edge of the metal-oxide-silicon field-effect transistor (MOSFET) sidewall spacer. The observation of void growth with the postannealing time supports this hypothesis. The observed void shape agrees well with a numerical simulation driven by the minimization of the interfacial free energy. The void serves as a resistance in the current–voltage characteristics of MOSFET devices.

Formation of epitaxial CoSi2 spike in Co/Si3N4/Si(100) system and its crystallographic structure

The formation of CoSi2 spike in the Co/Si3N4/Si(100) system and its crystallographic structure have been investigated. An annealing at 1050 °C caused not only agglomeration of Co film but penetration of Co agglomerates through the Si3N4 layer. The CoSi2 spike of B type epitaxial and twinned orientation of CoSi2[110]∥Si[110], Si(111)∥CoSi2(111) and Si(111)∥CoSi2(111) was formed in the Si substrate by the penetrated Co source. The formation of the epitaxial CoSi2 spike can be explained by the fast diffusion of Co atoms along defects in Si such as dislocations resulting from stress between the Si3N4 layer and the Si substrate.

Effects of Potassium Ion Substitution on Lattice Parameters and Proton Migration in Barium Phosphate

The effects of substituting a potassium ion for a barium ion in barium phosphate on lattice parameters and proton migration were investigated using density functional theory. A proton inserted into the material preferred to be attached to an oxygen ion near the potassium ion to compensate for the positive charge of the potassium ion that is less than that of the barium ion. Lattice parameters were investigated as a function of the potassium ion concentration. The lattice parameter a increased linearly with the potassium ion concentration, while the lattice parameter c remained almost constant. These trends were in good agreement with the experimental results. When the proton migrated from the ab-plane containing the potassium ion to the plane free of the potassium ion, a high energy barrier of 0.58 eV was required for proton migration. This value was also in good agreement with the experimentally measured energy barriers (0.53–0.58 eV).

Interaction Effect of Protons on Their Migration in Bulk Undoped Barium Zirconate Using Density Functional Theory

The interaction effect of two protons on their migration in bulk barium zirconate was investigated to understand the difference between experimental and calculated energy barriers for proton migration using density functional theory. There were four different proton structure configurations in terms of proton interaction distance; symmetrically distorted, undistorted, symmetrically/asymmetrically distorted, and asymmetrically distorted. The asymmetrically distorted structure was obtained with the shortest distance between the two protons and was energetically the most stable. A high energy barrier of 0.41 eV was required for proton migration when a proton migrated near another proton owing to their repulsive interaction with each other and attractive interaction with neighboring oxygen ions. Therefore, the interaction between protons can contribute to reducing the difference between experimental and calculated energy barriers for proton migration in bulk barium zirconate.

A Study on High Frequency-Plasma Enhanced Chemical Vapor Deposition Silicon Nitride Films for Crystalline Silicon Solar Cells

SiNx:H films have been widely used for anti-reflection coatings and passivation for crystalline silicon solar cells. In this study, SiNx:H films were deposited using high frequency (13.56 MHz) direct plasma enhanced chemical vapor deposition, and the optical and passivation properties were investigated. The radio frequency power, the spacing between the showerhead and wafer, the ratio, the total gas flow, and the gas flow were changed over certain ranges for the film deposition. The thickness uniformity, the refractive index, and the minority carrier lifetime were then measured in order to study the properties of the film. The optimal deposition conditions for application to crystalline Si solar cells are determined from the results of this study.