Woo-Byoung Kim

Ultrathin SiO2 layer with an extremely low leakage current density formed in high concentration nitric acid

An ultrathin silicon dioxide (SiO2) layer of 1.2–1.4 nm thickness has been formed by immersion of Si wafers in nitric acid (HNO3) aqueous solutions, and its electrical characteristics and physical properties are investigated as a function of the HNO3 concentration. Measurements of transverse optical and longitudinal optical phonons of Si–O–Si asymmetric stretching vibrational mode for SiO2 indicate that the atomic density of the SiO2 layer increases with the HNO3 concentration. X-ray photoelectron spectroscopy measurements show that the valence band discontinuity energy at the SiO2/Si interface also increases and the concentration of suboxide species decreases with the HNO3 concentration. The leakage current density of the ⟨Al/SiO2/Si(100)⟩ metal-oxide-semiconductor (MOS) diodes with the SiO2 layer formed in HNO3 aqueous solutions decreases with the HNO3 concentration and also decreases by postmetallization annealing (PMA) treatment at 250 °C in 5 vol % hydrogen atmosphere. For the MOS diodes with the SiO...

Ultrathin SiO2 layer on atomically flat Si(111) surfaces with excellent electrical characteristics formed by nitric acid oxidation method

We have developed a method of formation of atomically smooth Si∕SiO2 interfaces by oxidation of atomically flat Si(111) surfaces by use of azeotropic nitric acid (HNO3) aqueous solutions (i.e., 68wt% HNO3 at 121°C). For the SiO2 layer on the atomically smooth Si substrates, the concentration of suboxide species, Si2+, is ∼50% of that on the rough Si substrates, and the valence band discontinuity is higher by ∼0.1eV. In this case, the leakage current flowing through the ∼1.2nm SiO2 is low, and further decreased by postmetallization annealing at 250°C in hydrogen (e.g., 0.5A∕cm2 at VG=1V).

Ultrathin SiO2 layer with a low leakage current density formed with ~ 100% nitric acid vapor

An ultrathin silicon dioxide (SiO(2)) layer with 0.65-1.5 nm thickness has been formed by approximately 100% nitric acid (HNO(3)) vapor oxidation, and its electrical characteristics and physical properties are investigated. The oxidation kinetics follows a parabolic law except for the ultrathin (<or=0.8 nm) region, indicating that diffusion of oxidizing species (i.e. oxygen atoms generated by decomposition of approximately 100% HNO(3) vapor) through a growing SiO(2) layer is the rate-determining step. The diffusion activation energy for HNO(3) vapor oxidation is 0.14 eV, much lower than that of thermal oxidation of 1.24 eV. The leakage current density for the 0.65 nm SiO(2) layer formed by HNO(3) vapor oxidation is lower by approximately one order of magnitude than that for a thermal oxide layer with the same thickness. The low leakage current density is attributed to (i) the atomically flat SiO(2)/Si interface and uniform thickness of the ultrathin SiO(2) layer, (ii) the low concentration of suboxide species and the low interface state density and (iii) the high atomic density of the SiO(2) layer, which leads to a high band discontinuity energy at the SiO(2)/Si interface. The leakage current density is further decreased by PMA at 250 degrees C in 5 vol% H(2) atmosphere.

MtDNA Haplogroups and Elite Korean Athlete Status

Mitochondrial DNA (mtDNA) variation has recently been suggested to have an association with athletic performance or physical endurance. Since mtDNA is haploid and lacks recombination, specific mutations in the mtDNA genome associated with human exercise tolerance or intolerance arise and remain in particular genetic backgrounds referred to as haplogroups. To assess the possible contribution of mtDNA haplogroup-specific variants to differences in elite athletic performance, we performed a population-based study of 152 Korean elite athletes [77 sprint/power athletes (SPA) and 75 endurance/middle-power athletes (EMA)] and 265 non-athletic controls (CON). The overall haplogroup distribution of EMA differed significantly from CON (p<0.01), but that of SPA did not. The EMA have an excess of haplogroups M* (OR 4.38, 95% CI 1.63-11.79, p=0.003) and N9 (OR 2.32, 95% CI 0.92-5.81, p=0.042), but a dearth of haplogroup B (OR 0.26, 95% CI 0.09-0.75, p=0.003) compared with the CON. Thus, our data imply that specific mtDNA lineages may provide a significant effect on elite Korean endurance status, although functional studies with larger sample sizes are necessary to further substantiate these findings.

Study of density of interface states in MOS structure with ultrathin NAOS oxide

The quality of the interface region in a semiconductor device and the density of interface states (DOS) play important roles and become critical for the quality of the whole device containing ultrathin oxide films. In the present study the metal-oxide-semiconductor (MOS) structures with ultrathin SiO2 layer were prepared on Si(100) substrates by using a low temperature nitric acid oxidation of silicon (NAOS) method. Carrier confinement in the structure produces the space quantization effect important for localization of carriers in the structure and determination of the capacitance. We determined the DOS by using the theoretical capacitance of the MOS structure computed by the quantum mechanical approach. The development of the density of SiO2/Si interface states was analyzed by theoretical modeling of the C-V curves, based on the superposition of theoretical capacitance without interface states and additional capacitance corresponding to the charges trapped by the interface states. The development of the DOS distribution with the passivation procedures can be determined by this method.

Room-temperature processing of CdSe quantum dots with tunable sizes

In this work, CdSe quantum dots (QDs) with tunable sizes have been fabricated via photo-induced chemical etching at room temperature, and the related reaction mechanism was investigated. The surface of QDs was oxidized by the holes generated through photon irradiation of oxygen species, and the obtained oxide layer was dissolved in an aqueous solution of 3-amino-1-propanol (APOL) with an APOL:H2O volume ratio of 5:1. The generated electrons promoted QD surface interactions with amino groups, which ultimately passivated surface defects. The absorption and photoluminescence emission peaks of the produced QDs were clearly blue-shifted about 26 nm with increasing time, and the resulting quantum yield for an 8 h etched sample was increased from 20% to 26%, as compared to the initial sample.

Ultrathin ZnS and ZnO Interfacial Passivation Layers for Atomic-Layer-Deposited HfO2 Films on InP Substrates.

Ultrathin ZnS and ZnO films grown by atomic layer deposition (ALD) were employed as interfacial passivation layers (IPLs) for HfO2 films on InP substrates. The interfacial layer growth during the ALD of the HfO2 film was effectively suppressed by the IPLs, resulting in the decrease of electrical thickness, hysteresis, and interface state density. Compared with the ZnO IPL, the ZnS IPL was more effective in reducing the interface state density near the valence band edge. The leakage current density through the film was considerably lowered by the IPLs because the film crystallization was suppressed. Especially for the film with the ZnS IPL, the leakage current density in the low-voltage region was significantly lower than that observed for the film with the ZnO IPL, because the direct tunneling current was suppressed by the higher conduction band offset of ZnS with the InP substrate.

Resistive switching characteristics of Au/P-doped NiO/Au segmented nanowires synthesized by electrochemical deposition

In this paper, we detail the synthesis and characteristics of Au/NiO/Au segmented nanowire-based resistive switching memory devices. The fabrication of the memory devices involves the step-by-step electrodeposition of Au–Ni–Au into an anodic aluminum oxide template followed by the thermal oxidation process to make NiO. The unipolar resistive change is observed in Au/NiO/Au nanowires exhibiting a set voltage of 0.6 V and a reset voltage of 1 V with a current compliance of 10 mA. Au diffused Au into NiO during the thermal oxidation lowers the resistance of NiO and the forming voltage. The change in the switching behavior from unipolar to bipolar is achieved by doping approximately 3 at. % phosphorous in the interface of NiO and a Au electrode.

X-ray photoelectron spectroscopy analysis of TlInGaAsN semiconductor system and their annealing-induced structural changes

TlInGaAsN thin films grown by gas-source molecular-beam epitaxy were investigated by x-ray photoelectron spectroscopy (XPS) to analyze the Tl incorporation and to study the annealing-induced transformation of the atomic configurations. XPS analysis revealed that the Tl composition in the grown TlInGaAsN is around 1.5% and that the dominant atomic configuration of the TlInGaAsN changes from the In–As and Ga–N bonds to the In–N and Ga–As bonds by 700 °C rapid thermal annealing. High-resolution x-ray diffraction and reciprocal space mapping measurements showed that no significant out-diffusion of the elements occurs in the TlInGaAsN/TlGaAsN quantum wells (QWs) even after the same annealing. It is concluded that the blueshift in the photoluminescence peak for the TlInGaAsN/TlGaAsN QWs after annealing is attributed to the transformation of the atomic configuration in TlInGaAsN.

The Preparation of Dye-Sensitized Solar Cell Paste Used the Peroxo Titanium Complex and Characteristics by Annealing Temperature

The organic binder-free paste for dye-sensitized solar cell (DSSC) has been investigated using peroxo titanium complex. The crystal structure of nanoparticles, morphology of film and electrical properties are analyzed by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectra (EIS), and solar simulator. The synthesized nanopowders by the peroxo titanium complex at 150, 300, , and have anatase phase and average crystal sizes are calculated to be 4.2, 13.7, 16.9, and 20.9 nm, respectively. The DSSC prepared by the peroxo titanium complex binder have higher and lower values than that of the organic binder. It can be attributed to improvement of sintering properties of and interface and to formation of agglomerate by the nanoparticles. As a result, we have investigated the organic binder-free paste and 3.178% conversion efficiency of the DSSC at .