Ulsan National Institute of Science and Technology · Materials Science
Professor Jiwon Chang's research lab specializes in the electronic properties and device applications of two-dimensional and topological materials, with a focus on quantum transport phenomena, heterostructure engineering, and nanoscale field-effect transistors. The lab employs advanced first-principles and atomistic simulations to explore novel semiconductor and topological insulator-based devices, including TFETs, MOSFETs, and heterostructures with thickness-dependent phase transitions. Key research directions include the design of low-power, high-performance transistors using materials like monolayer MoS₂, antimonene, and PdSe₂, as well as the fundamental understanding of surface states and band gap engineering in 2D and 3D topological insulators. The lab also develops compact models for short-channel devices to bridge quantum simulations with practical device design.
Figures are computed from collected data and may differ slightly.
We study the transport properties of deeply scaled monolayer MoS2 n-channel metal-oxide-semiconductor field effect transistors (MOSFETs), using full-band ballistic quantum transport simulations, with an atomistic tight-binding Hamiltonian obtained from density functional theory. Our simulations suggest that monolayer MoS2 MOSFETs can provide near-ideal subthreshold slope, suppression of drain-induced barrier lowering, and gate-induced drain leakage. However, these full-band simulations exhibit l
Three-dimensional (3-D) topological insulators (TIs) are characterized by the presence of metallic surface states and a bulk band gap. Recently, theoretical and experimental studies have shown an induced gap in the surface state bands of TI thin films. The gap results from interaction of conduction band and valence band surface states from the opposite surfaces of a thin film, and its size is determined by the film thickness. This gap formation could open the possibility of thin-film TI-based me
In this paper, we propose a compact model of the short-channel double-gate (DG) JFETs, which are devices intended for low-power logic applications. In order to make the current equation continuous through all operating conditions from the subthreshold to well above the threshold without nonphysical fitting parameters, mobile carriers in depletion regions are considered. For describing the short-channel behavior, relevant parameters extracted from the 2-D analytical solution of Poisson's equation
Using an ab initio density functional theory based electronic structure method with a semilocal density approximation, we study thin-film electronic properties of two topological insulators based on ternary compounds of Tl (thallium) and Bi (bismuth). We consider TlBi${X}_{2}$ ($X=$ Se, Te) and Bi${}_{2}$${X}_{2}Y$ ($X,Y=$ Se,Te) compounds which provide better Dirac cones, compared to the model binary compounds Bi${}_{2}$${X}_{3}$($X=$ Se, Te). With this property in combination with a structural
Recently, a mono-elemental two-dimensional (2-D) material, namely antimonene, with a large band gap, decent mobility and ambient stability has been extensively researched. Interestingly, although antimonene is a semiconductor with a sizable band gap in the monolayer, it is transformed to a metal in the multilayer. Inspired by this thickness dependent semiconductor to metal transition, we propose novel antimonene tunneling field-effect transistors (TFETs) based on the lateral monolayer (semicondu
Abstract The thickness‐modulated phase transition from semi‐metallic (bulk) to semiconductor (a few layers) is the most unique property of pentagonal palladium diselenide (PdSe 2 ). Thus, precise thickness tailoring is essential to fully utilize its unique thickness‐dependent property for exotic device applications. Here, tunable current transport in PdSe 2 based field‐effect transistors (FETs) enabled by layer‐by‐layer thinning of PdSe 2 using mild SF 6 :N 2 plasma is presented. With this top‐d
Metal conversion processes have been instrumental in advancing semiconductor technology by facilitating the growth of thin-film semiconductors, including metal oxides and sulfides. These processes, widely used in the industry, enhance the semiconductor manufacturing efficiency and scalability, offering convenience, large-area fabrication suitability, and high throughput. Furthermore, their application to emerging two-dimensional (2D) semiconductors shows promise in addressing spatial control and
Achieving effective polarity control of n- and p-type transistors based on two-dimensional (2D) materials is a critical challenge in the process of integrating transition metal dichalcogenides (TMDC) into complementary metal-oxide semiconductor (CMOS) logic circuits. Herein, we utilized a proficient and nondestructive method of electron-charge transfer to achieve a complete carrier polarity conversion from p-to n-type by depositing a thin layer of aluminum oxide (Al<sub>2</sub>O<sub>3</sub>) ont
High contact resistance (R<sub>c</sub>) limits the ultimate potential of two-dimensional (2-D) materials for future devices. To resolve the R<sub>c</sub> problem, forming metallic 1T phase MoS<sub>2</sub> locally in the semiconducting 2H phase MoS<sub>2</sub> has been successfully demonstrated to use the 1T phase as source/drain electrodes in field effect transistors (FETs). However, the long-term stability of the 1T phase MoS<sub>2</sub> still remains as an issue. Recently, an unusual thickness
Using a density-functional-based electronic structure method, we study the effect of crystalline dielectrics on the metallic surface states of Bismuth- and chalcogen-based binary and ternary three-dimensional topological insulator (TI) thin films. Crystalline quartz (SiO(2)) and boron nitride (BN) dielectrics were considered. Crystalline approximation to the amorphous quartz allows one to study the effect of oxygen coverage or environmental effects on the surface-state degradation, which has gai
Abstract In this work, electrically binary and ternary reconfigurable complementary metal‐oxide‐semiconductor (T‐CMOS) inverter that achieves stable multivalued logic (MVL) is presented. The device is realized through vertical integration of chemical vapor deposition‐grown MoS 2 n‐channel and WSe 2 p‐channel metal‐oxide‐semiconductor field‐effect transistors (MOSFETs) in a complementary FETs (CFETs) configuration, combined with a gate‐tunable MoS₂ resistive element that enables a well‐defined in
We study the transport properties of monolayer transition metal Dichalcogenides (TMDs) MX <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (M = Mo, W; X = S, Se, Te) n-channel metal-oxide-semiconductor field effect transistors (MOSFETs) using an atomistic tight-binding full-band ballistic quantum transport simulations, with hopping potentials obtained from density functional theory. We discuss the subthreshold slope (SS), drain-induced barrie
Transport properties of about 3 nm channel length monolayer MoX2 (X = S, Se, Te) n-channel metal-oxide-semiconductor field effect transistors (MOSFETs) are examined through ballistic full-band quantum transport simulations with atomistic tight-binding Hamiltonians. Our simulations reveal that single gate (SG) monolayer MoX2 MOSFETs with an approximately 2 nm gate underlap exhibit reasonable subthreshold characteristics. From these full-band simulations, we observe channel orientation dependent n
Abstract In this work, a theoretical study on the electronic properties of the metal/Bi 2 O 2 Se interface is presented through the density functional theory calculation. Particularly, the effects of Cr, Pd, Pt, Au, and Bi on monolayer, bilayer, and trilayer Bi 2 O 2 Se are explored. Naturally created Se vacancies on the Bi 2 O 2 Se surface are also considered by constructing two interface structures: the metal/Bi 2 O 2 Se with the Se vacancies remaining or filled with metals. For the metal/mono
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