Sungjoo Lee

High speed photodetectors are a key building block, which allow a large wavelength range of detection from 850 nm to telecommunication standards at optical fiber band passes of 1.3-1.55 μm. Such devices are key components in several applications such as local area networks, board to board, chip to chip and intrachip interconnects. Recent technological achievements in growth of high quality SiGe/Ge films on Si wafers have opened up the possibility of low cost Ge-based photodetectors for near infr

The physical and chemical properties of MXenes are strongly dependent on surface terminations; thus, the tailoring of surface functional groups in two-dimensional transition-metal carbides (MXenes) may extend the applicability of these compelling materials to a wider set of fields. In this work, we demonstrate the chemical modification of Ti3C2Tx MXene via diazonium covalent chemistry and the subsequent effects on the electrical properties of MXene. The 4-nitrophenyl group was grafted onto the s

Channel current conduction modulation with the spontaneous polarization of ferroelectric films in ferroelectric field-effect transistors (FeFETs) has been widely investigated. Low interface quality and thermodynamic instability owing to the presence of dangling bonds in the conventional ferroelectrics have limited the memory retention and endurance of FeFETs. This, in turn, prevents their commercialization. However, the atomically thin nature of 2D ferroelectric, semiconducting, and insulating f

To address the demands of emerging data-centric computing applications, ferroelectric field-effect transistors (Fe-FETs) are considered the forefront of semiconductor electronics owing to their energy and area efficiency and merged logic-memory functionalities. Herein, the fabrication and application of an Fe-FET, which is integrated with a van der Waals ferroelectrics heterostructure (CuInP₂ S₆ /α-In₂ Se₃ ), is reported. Leveraging enhanced polarizati

We demonstrate that HfO₂, a high-K dielectric, can be prepared on the top surface of 2D HfS₂ through plasma oxidation, which results in a heterostructure composed of a 2D van der Waals semiconductor and its insulating native oxide.

Abstract A novel hybrid phototransistor consisting of molybdenum carbide (Mo 2 C) and molybdenum disulfide (MoS 2 ) is proposed. By exploiting the interface properties of MoS 2 and Mo 2 C, a highly sensitive and broad‐spectral response photodetector is fabricated. The underlying mechanism of the enhanced performance is the efficient hot carrier injection from Mo 2 C to MoS 2 . The strong coupling of MoS 2 and Mo 2 C at the interface provides the significantly low Schottky barrier height (≈70 meV

Abstract Two‐dimensional (2D) layers of transition metal carbides, nitrides, or carbonitrides, collectively referred to as MXenes, are considered as the new family of 2D materials for the development of functional building blocks for optoelectronic and photonic device applications. Their advantages are based on their unique and tunable electronic and optical properties, which depend on the modulation of transition metal elements or surface functional groups. In this paper, we have presented a co

Rapid developments in artificial neural network techniques and retina-inspired artificial visual systems are required to realize the sensing, processing, and memorization of an optical signal in a single device. Herein, a ferroelectric field-effect transistor fabricated with CuInP₂S₆ and α-In₂Se₃ van der Waals heterostructures is proposed and demonstrated for the development of an artificial visual system. The dipole polarizations are coupled and bidir

MXenes, an emerging class of two-dimensional (2D) transition metal carbides and nitrides, have attracted wide attention because of their fascinating properties required in functional electronics. Here, an atomic-switch-type artificial synapse fabricated on Ti₃ C₂ T_x MXene nanosheets with lots of surface functional groups, which successfully mimics the dynamics of biological synapses, is reported. Through in-depth analysis by X-ray photoelectron spectroscopy, tran

Platinum diselenide (PtSe2), a recently rediscovered two-dimensional transition metal dichalcogenide, has attracted immense attention in the optoelectronic field due to its tunable bandgap, ultrastability, and high electron mobility. However, the applications of PtSe2 photodetectors are seriously restricted by their low responsivity. In this work, a high-responsivity (5 × 104 A/W) PtSe2 photodetector is obtained by exploiting a photogating effect; this is induced by the hole-trapping states, whi