Seokhyun Yoon

Hydroxyl radical-assisted decomposition and oxidation in solution-processed indium oxide thin-film transistors

Solution-processed indium oxide TFTs were fabricated by hydroxyl radical-assisted (HRA) decomposition and oxidation. The results show that decomposition and oxidation of carbon is more substantial than metal hydroxides, leading to the elimination of organic residues, correlated to a low interface trap density (S.S. = 0.45 V dec−1, NT = 1.11 × 1012 cm−2) in the device. The resultant HRA indium oxide TFTs exhibit improved electrical characteristics such as the mobility, the on/off current ratio, and the subthreshold swing as well as bias stabilities under PBS and NBS conditions.

A solution-processed quaternary oxide system obtained at low-temperature using a vertical diffusion technique

We report a method for fabricating solution-processed quaternary In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) at low annealing temperatures using a vertical diffusion technique (VDT). The VDT is a deposition process for spin-coating binary and ternary oxide layers consecutively and annealing at once. With the VDT, uniform and dense quaternary oxide layers were fabricated at lower temperatures (280 °C). Compared to conventional IGZO and ternary In-Zn-O (IZO) thin films, VDT IGZO thin film had higher density of the metal-oxide bonds and lower density of the oxygen vacancies. The field-effect mobility of VDT IGZO TFT increased three times with an improved stability under positive bias stress than IZO TFT due to the reduction in oxygen vacancies. Therefore, the VDT process is a simple method that reduces the processing temperature without any additional treatment for quaternary oxide semiconductors with uniform layers.

Electrical stability enhancement of GeInGaO thin-film transistors by solution-processed Li-doped yttrium oxide passivation

In this study, we investigated a method of enhancing the electrical stability of GeInGaO thin-film transistors (TFTs) using a Li-doped Y2O3 (YO) passivation layer (PVL). Li reduced metal hydroxide groups in the PVL, and diffused into the channel layer and reduced the oxygen vacancy at the top surface of the channel layer, which is the origin of the defect state and electrical instability. In addition, the negative-bias temperature stress (NBTS) for 3600 s improved for Li-doped YO (LYO) PVL. The threshold voltage shift decreased from −10.3 V for the YO PVL to −4.8 V for the LYO PVL, a 54% improvement.

Modification of hybrid active bilayer for enhanced efficiency and stability in planar heterojunction colloidal quantum dot photovoltaics

Solution-processed planar heterojunction colloidal quantum dot photovoltaics with a hybrid active bilayer is demonstrated. A power conversion efficiency of 1.24% under simulated air mass 1.5 illumination conditions is reported. This was achieved through solid-state treatment with cetyltrimethylammonium bromide of PbS colloidal quantum dot solid films. That treatment was used to passivate Br atomic ligands as well as to engineer the interface within the hybrid active bilayer.