Kyung Park

Disseminated Epidermolytic Acanthoma with Disseminated Superficial Porokeratosis and Verruca Vulgaris in an Immunosuppressed Patient

A 40‐year‐old man who had received long term immunosuppressive treatment for 14 years following kidney transplantation developed multiple skin lesions on both antecubital fossae, scalp, and both lower extremities. Histopathologic findings from three skin regions revealed characteristic features of epidermolytic hyperkeratosis, verruca vulgaris, and disseminated superficial porokeratosis, respectively.

Influence of post-annealing on the off current of MoS2 field-effect transistors

Two-dimensional materials have recently been spotlighted, due to their unique properties in comparison with conventional bulk and thin-film materials. Among those materials, MoS2 is one of the promising candidates for the active layer of electronic devices because it shows high electron mobility and pristine band gap. In this paper, we focus on the evolution of the electrical property of the MoS2 field-effect transistor (FET) as a function of post-annealing temperature. The results indicate that the off current drastically decreased at 200°C and increased at 400°C while other factors, such as the mobility and threshold voltage, show little variation. We consider that the decreasing off current comes from the rearrangement of the MoS2 film and the elimination of the surface residue. Then, the increasing off current was caused by the change of the materials composition and adsorption of H2O and O2.

Effect of Active Layer Thickness on Device Performance of Tungsten-Doped InZnO Thin-Film Transistor

Tungsten (~4 at. %)-doped InZnO thin-film transistors were fabricated as a function of the active layer thickness using an RF sputtering system. To explain the degradation of the device performance in relation to the changes of the active layer thickness, the correlations between the device performance and the physical properties, including the film density, surface/interface roughness, band edge state below the conduction band, refractive index, and composition along the depth direction were investigated. Tungsten-doped indium-zinc oxide (WIZO) TFTs with active layer thickness of 10 nm exhibited the highest field effect mobility of 19.57 cm2/Vs and the lowest threshold voltage shift of 0.62 V. The enhancement of the device performance is strongly correlated with the highest film density and a flat interface roughness of SiO2-WIZO. In addition, interface layer thickness and band edge states below the conduction band were changed with increasing active layer thickness. These remarkable changes in the interface layer thickness and band edge state could be correlated to changes in the device performance.

A study on materials interactions between Mo electrode and InGaZnO active layer in InGaZnO-based thin film transistors

This study examined the degradation of the device performance of InGaZnO4 (IGZO)based thin-film transistors after annealing at high temperatures in air ambient. Using various characterization methods including scanning electron microscopy, x-ray diffraction, and transmission electron microscopy, we were able to disclose the details of a two-stage phase transformation that led to the device performance degradation. The Mo electrodes first succumbed to oxidation at moderate temperatures (400 500 C) and then the Mo oxide further reacted with IGZO to produce an In–Mo–O compound with some Ga at higher temperatures (600 700 C). We analyzed our results based on the thermodynamics and kinetics data available in the literature and confirmed that our findings are in agreement with the experimental results.

Extensive Aberrant Mongolian Spot

A 9‐month‐old male infant had generalized diffuse blue‐gray pigmentation over most of his body, sparing the scalp, face, neck, palms, soles, periumbilical area, genital area, and nipples. Within the lesion, there were several conspicuous macules of considerably darker hue. Histologic examination revealed numerous dermal melanocytes. By 16 months of age, the childs blue‐gray pigmentation had decreased substantially.

Reliability of Crystalline Indium–Gallium–Zinc-Oxide Thin-Film Transistors Under Bias Stress With Light Illumination

We investigate the effect of crystalline indium-gallium-zinc-oxide (c-IGZO) thin films on device performance, and evaluate the device reliability of c-IGZO under positive/negative bias stress with/without illumination. The crystal structure of deposited-IGZO thin film is controlled by annealing temperatures, and the transition from an amorphous to a crystalline structure is observed at above 800 °C. Even though the c-IGZO thin-film transistors (TFTs) exhibit lower carrier mobility, compared with amorphous IGZO (a-IGZO) TFTs, the remarkable improvement of the device reliability for the c-IGZO TFTs is observed especially under the bias stress with illumination. This comes from lower defect density compared with the a-IGZO film.

A transparent solar cell based on a mechanically exfoliated GaTe and InGaZnO p-n heterojunction

Two-dimensional (2D) materials are known for their unique properties and potential for application in various electronic and optoelectronic devices. Since 2D semiconductors have weak bonding between the layers, they can be easily separated into several nanometer-thick layers which still maintain their characteristics. GaTe is a p-type 2D semiconductor having a direct bandgap. By combining multi-layer GaTe and thin-film IGZO, we have fabricated a p–n heterojunction, a fundamental unit of optoelectronic devices. In this paper, we propose the first fully transparent solar cell using a 2D material, based on a GaTe/IGZO heterostructure. The device shows a high transparency of ∼90% and an efficiency of 0.73% with a fill factor of 37%. It exhibits instantaneous generation of photo-carriers under periodic light pulses. Further analysis of the operating mechanism was conducted by studying its band alignments. The transparency of our GaTe/IGZO solar cell can overcome its relatively low efficiency, as it can be installed in a much larger scale and the total amount of generated power will surpass that of the conventional solar cell. Furthermore, advances in the large-scale growth of GaTe will enhance the power conversion efficiency, and finally enable the adoption of 2D active layer based highly transparent, thin-film solar cells for building integrated photovoltaic systems.

Impact of bias stability for crystalline InZnO thin-film transistors

Crystallized InZnO thin-film transistors (IZO TFTs) are investigated to identify a potential for the maintenance of high electrical performances with a consistent stability. The transition from an amorphous to a crystallization structure appeared at an annealing temperature around 800 °C, and it was observed using transmission electron microscopy and time-of-flight secondary ion mass spectrometry analysis. The field-effect mobility of the crystallized IZO TFTs was boosted up to 53.58 cm2/V s compared with the 11.79 cm2/V s of the amorphous devices, and the bias stability under the negative stress was greatly enhanced even under illumination. The defect states related to the oxygen vacancy near the conduction band edge decreased after the crystallization, which is a form of electrical structure evidence for the reliability impact regarding the crystallized IZO TFTs.

Effects of Fluorine Doping on the Electrical Performance of ZnON Thin-Film Transistors

In this work, the effects of fluorine incorporation in high mobility zinc oxynitride (ZnON) semiconductor are studied by both theoretical calculations and experimental evaluation of thin film transistors (TFTs). From density functional theory (DFT) calculations, fluorine acts as a carrier suppressor in the ZnON matrix when it substitutes a nitrogen vacant site (VN). Thin films of ZnON and ZnON:F were grown by reactively cosputtering Zn metal and ZnF2 targets, and their electrical, physical, and chemical characteristics were studied. X-ray photoelectron spectroscopy (XPS) analyses of the nitrogen 1s peaks in ZnON and ZnON:F suggest that as the fluorine incorporation increases, the relative fraction of Zn-N bonds from stoichiometric Zn3N2 increases. On the other hand, the Zn-N bond characteristics arising from nonstoichiometric ZnxNy and N-N bonds decrease, implying that indeed fluorine anions have an effect of passivating the N-related defects. The corresponding TFTs exhibit optimum transfer characteristics and switching ability when approximately 3.5 atomic percent of fluorine is present in the 40 nm thick ZnON:F active layer.

Erratum to: A study on the competition between bias-induced charge trapping and light-induced instability in In-Ga-Zn-O thin-film transistors

Thin-film transistors (TFTs) were fabricated using In-Ga-Zn-O (IGZO) semiconductor layers deposited under different oxygen partial pressures. The devices were subjected to negative bias stress (NBS), negative bias illumination stress (NBIS), positive bias stress (PBS) and positive bias illumination stress (PBIS). While device degradation is negligible under NBS, negative shifts in the threshold voltage (Vth) are observed in the presence of light (NBIS), of which the magnitude (ΔVth) decreases with increasing oxygen partial pressure during IGZO growth. Under PBS, the devices undergo positive Vth shifts, which become more severe with increasing oxygen content in IGZO. However, negative ΔVth values are observed under PBIS, of which the magnitude decreases with increasing oxygen content in the semiconductor. When positive gate bias is applied, the trapping of negative charge by interstitial oxygen atoms in IGZO is presumed to be the driving force inducing positive Vth shifts. On the other hand, when light is present, the generation of photo-induced excess carriers from oxygen-deficient defect sites is anticipated to be the driving force inducing negative Vth shifts. A balance between the competing mechanisms inducing either positive or negative Vth shifts must therefore be established when the devices are subjected to PBIS, for example in operating active matrix organic light emitting diode (AMOLED) displays using transparent panel arrays.