Yoon Jang Chung

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Optically more stable, high mobility InGaZnO thin film transistors were fabricated by implementing ultrathin In2O3-SnO2 (ITO) layers at the gate dielectric/semiconductor interface. The optimized device portrayed a high saturation mobility of ∼80 cm2/V s with off current values lower than 10−11A. The ITO layer also acted as a hole filter layer, and hole current and threshold voltage shift values measured under negative bias illumination conditions showed that a significant amount of photo-generat

Degenerate conduction-band minima, or ``valleys'', in materials such as Si, AlAs, graphene, and ${\mathrm{MoS}}_{2}$ allow them to host two-dimensional electron systems (2DESs) that can access a valley degree of freedom. These multivalley 2DESs present exciting opportunities for both pragmatic and fundamental research alike because not only are they a platform for valleytronic devices, but they also provide a tool to tune and investigate the properties of complex many-body ground states. Here, w

Local doping of Al:ZnO into a ZnO matrix was performed vertically at various positions in a thin film using atomic layer deposition, and its influence was investigated by analyzing thin film transistor (TFT) characteristics. The position specific dopant distribution in the films was confirmed by high resolution transmission electron microscopy. It was found that doping specific locations in the active channel layer of a TFT had a different impact on its electrical characteristics. When near the

Capacitor structures utilized in modern dynamic random access memory (DRAM) cells require the conformal growth of high- k films on electrode materials. In this context, the atomic layer deposition (ALD) of rutile-phase TiO 2 on nearly lattice-matched substrates such as RuO 2 has been extensively explored. It is typically desired to grow such insulating films at high temperatures to ensure low defect concentrations and high crystallinity. However, with increasing growth temperature, it is also cr

In general, the electronic and optical properties of oxide films can significantly benefit from highly textured crystallinity. However, oxide films grown by atomic layer deposition (ALD), a powerful technique for the synthesis of high-quality, nanoscale thin films, usually exhibit amorphous or randomly oriented polycrystalline phases. Here, we demonstrate the growth of highly textured rutile phase ALD TiO 2 films through rational substrate design. Both a - and c -axis preferentially oriented TiO

The complex band structure, large spin-orbit induced band splitting, and heavy effective mass of two-dimensional (2D) hole systems hosted in GaAs quantum wells render them rich platforms to study many-body physics and ballistic transport phenomena. Here we report ultra-high-quality (001) GaAs 2D hole systems, fabricated using molecular beam epitaxy and modulation doping, with mobility values as high as $5.8\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}$/(V s

Suppressing electron scattering is essential to achieve high-mobility two-dimensional electron systems (2DESs) that are clean enough to probe exotic interaction-driven phenomena. In heterostructures it is common practice to utilize modulation doping, where the ionized dopants are physically separated from the 2DES channel. The doping-well structure augments modulation doping by providing additional screening for all types of charged impurities in the vicinity of the 2DES, which is necessary to a

Abnormal hysteresis was found to exist in amorphous Hf-In-Zn-O thin film transistors under illumination. Unlike common hysteresis, a disparity in the sub-threshold swing of the transfer curves was observed. This distinction showed a linear increase according to light intensity, and is thought to come from the light enabled motion of ionized oxygen vacancies (VO 2+). The positively charged nature of these defects causes them to show a different distribution in the channel according to sweep direc

Hole current was directly observed in oxide semiconductors under illumination. Two stacks were fabricated, with In-Ga-Zn-O (IGZO) as the channel and SiO2 or SiNx as the gate insulator. X-ray photoelectron spectroscopy confirmed the IGZO/SiNx interface has no hole barrier while the IGZO/SiO2 interface has a significant one. This was used to analyze hole generation in IGZO by illuminating light at various wavelengths. As a result, a threshold wavelength, where holes start to emerge in the channel,

We have developed a scanning photoluminescence technique that can directly map out the local two-dimensional electron density with a relative accuracy of ∼2.2 × 10⁸ cm^-2. The validity of this approach is confirmed by the observation of the expected density gradient in a high-quality GaAs quantum well sample that was not rotated during the molecular beam epitaxy of its spacer layer. In addition to this global variation in electron density, we observe local density fluctuatio

The development of highly conductive fibril‐type textile electrodes is crucial for the advancement of various smart wearable electronics including high‐performance energy storage devices. To achieve this goal, it is essential to convert insulating textiles into conductive counterparts while maintaining flexibility and porosity. Additionally, the incorporation of electrochemically active components into textile conductors enables tailor‐made textile energy electrodes for specific applications. Th

A simple optical model based on the transfer matrix method was used to simulate photon absorption in oxide semiconductor systems with varying insulator thickness in the thin film transistor (TFT) structure. For comparison with actual experimental results, hole current was measured in transparent metal/semiconductor/insulator/metal capacitor stacks under light illumination, and the threshold voltage shift under negative bias illumination stress conditions was also measured in the TFT structure. I