Won Jong Yoo

Motivated by the high expectation for efficient electrostatic modulation of charge transport at very low voltages, atomically thin 2D materials with a range of bandgaps are investigated extensively for use in future semiconductor devices. However, researchers face formidable challenges in 2D device processing mainly originated from the out-of-plane van der Waals (vdW) structure of ultrathin 2D materials. As major challenges, untunable Schottky barrier height and the corresponding strong Fermi le

A high-performance multilayer MoS2 p-type field-effect transistor is realized via controllable chemical doping, which shows an excellent on/off ratio of 10(9) and a maximum hole mobility of 132 cm(2) V(-1) s(-1) at 133 K. The developed technique will enable 2D materials to be used for future high-efficiency and low-power semiconductor device applications.

Abstract Two-dimensional (2D) materials hold great promise for future nanoelectronics as conventional semiconductor technologies face serious limitations in performance and power dissipation for future technology nodes. The atomic thinness of 2D materials enables highly scaled field-effect transistors (FETs) with reduced short-channel effects while maintaining high carrier mobility, essential for high-performance, low-voltage device operations. The richness of their electronic band structure ope

A systematic modulation of the carrier type in molybdenum ditelluride (MoTe₂ ) field-effect transistors (FETs) is described, through rapid thermal annealing (RTA) under a controlled O₂ environment (p-type modulation) and benzyl viologen (BV) doping (n-type modulation). Al₂ O₃ capping is then introduced to improve the carrier mobilities and device stability. MoTe₂ is found to be ultrasensitive to O₂ at elevated temperatures (250 °C

Currently 2D crystals are being studied intensively for use in future nanoelectronics, as conventional semiconductor devices face challenges in high power consumption and short channel effects when scaled to the quantum limit. Toward this end, achieving barrier-free contact to 2D semiconductors has emerged as a major roadblock. In conventional contacts to bulk metals, the 2D semiconductor Fermi levels become pinned inside the bandgap, deviating from the ideal Schottky-Mott rule and resulting in

This study illustrates the nature of electronic transport and its transition from one mechanism to another between a metal electrode and MoS2 channel interface in a field effect transistor (FET) device. Interestingly, measurements of the contact resistance (Rc) as a function of temperature indicate a transition in the carrier transport across the energy barrier from thermionic emission at a high temperature to tunneling at a low temperature. Furthermore, at a low temperature, the nature of the t

We report the first air-passivated ambipolar BP transistor formed by applying benzyl viologen, which serves as a surface charge transfer donor for BP flakes. The passivated BP devices exhibit excellent stability under both an ambient atmosphere and vacuum; their transistor performance is maintained semi-permanently. Unlike their intrinsic p-type properties, passivated BP devices present advantageous ambipolar properties with much higher electron mobility up to ∼83 cm(2) V(-1) s(-1) from 2-termin

This work investigates the use of oxygen plasma (O2) treatment, applied as an inductively coupled plasma, to control the thickness and work function of a MoS2 layer. Plasma-etched MoS2 exhibited a surface roughness similar to that of the pristine MoS2. The MoS2 field effect transistors fabricated using the plasma-etched MoS2 displayed a higher n-type doping concentration than that of pristine MoS2. The x-ray photoelectron spectroscopy was performed to analyze chemical composition to demonstrate

Pt patterns of the 0.25 µ m design rule were etched at 20° C using a magnetically enhanced reactive ion etcher. The main problem of this device integration process is the redeposition of the etch products onto the pattern sidewall, making it difficult to reduce the pattern size. In both cases using a photoresist mask and an oxide mask, the redeposits of the etch products onto the sidewall were reduced by the addition of Cl 2 to Ar, although the etch slope was lowered to 45°. Using the oxide mask

Despite the fact that the outstanding properties of graphene are well known, the electrical performance of the material is limited by the contact resistance at the metal-graphene interface. In this study, we demonstrate the formation of "edge-contacted" graphene through the use of a controlled plasma processing technique that generates a bond between the graphene edge and the contact metal. This technique controls the edge structure of the bond and significantly reduces the contact resistance. T

We investigate the development of gate-modulated tungsten diselenide (WSe₂)-based lateral pn-homojunctions for visible and near-infrared photodetector applications via an effective oxygen (O₂) plasma treatment. O₂ plasma acts to induce the p-type WSe₂ for the otherwise n-type WSe₂ by forming a tungsten oxide (WO<i>_x</i>) layer upon O₂ plasma treatment. The WSe₂ lateral pn-homojunctions displayed an enhanced p

Abstract The dielectric dispersion of a material holds significant importance for the understanding of basic material characteristics and the design parameters of a functional device. Here, the dielectric dispersion characteristics of multilayer hexagonal boron nitride (hBN) using time domain reflectometry under an extended device operating frequency range up to 100 MHz are studied. Contrary to what is previously reported, the capacitance, hence the effective dielectric constant, of hBN decrease

Abstract Effective control of 2D transistors polarity is a critical challenge in the process for integrating 2D materials into semiconductor devices. Herein, a doping‐free approach for developing tungsten diselenide (WSe 2 ) logic devices by utilizing the van der Waals (vdWs) bottom electrical contact with platinum and indium as the high and low work function metal respectively is reported. The device structure is free from chemical disorder and crystal defects arising from metal deposition, whi

We introduce an effective method to degenerately dope MoTe₂ by oxidizing its surface into the p-dopant MoO_<i>x</i> in oxygen plasma. As a self-terminated process, the oxidation is restricted only in the very top layer, therefore offering us an easy and efficient control. The degenerate p-doping with the hole concentration of 2.5 × 10¹³ cm^-2 can be obtained by applying a ∼300 s O₂ plasma treatment. Using the degenerately doped MoTe<sub>2</sub