Ambipolar Charge Transport in Two-Dimensional WS Metal-Insulator-Semiconductor and Metal-Insulator-Semiconductor Field-Effect Transistors.

Two-dimensional (2D) materials with ambipolar transport characteristics have attracted considerable attention as post-complementary metal-oxide semiconductor (CMOS) materials. These materials allow for electron- or hole-dominant conduction to be achieved in a single channel of the field-effect transistors (FETs) without an extrinsic doping. In this study, all-2D metal-insulator-semiconductor (MIS)-based devices, which were composed of all-2D graphene, hexagonal boron nitride, and WS, exhibited ambipolar and symmetrical transport characteristics with a low surface state density ( ≈ 7 × 10 cm·eV).

Monolithically Integrated Enhancement-Mode and Depletion-Mode β-GaO MESFETs with Graphene-Gate Architectures and Their Logic Applications.

Ultrawide band gap (UWBG) β-GaO is a promising material for next-generation power electronic devices. An enhancement-mode (E-mode) device is essential for designing power conversion systems with simplified circuitry and minimal loss. The integration of an E-mode field-effect transistor (FET) with a depletion-mode (D-mode) FET can build a high-performance logic circuit.

Heterostructure WSe-GaO Junction Field-Effect Transistor for Low-Dimensional High-Power Electronics.

Layered materials separated from each bulk crystal can be assembled to form a strain-free heterostructure by using the van der Waals interaction. We demonstrated a heterostructure n-channel depletion-mode β-GaO junction field-effect transistor (JFET) through van der Waals bonding with an exfoliated p-WSe flake. Typical diode characteristics with a high rectifying ratio of ∼10 were observed in a p-WSe/n-GaO heterostructure diode, where WSe and β-GaO were obtained by mechanically exfoliating each crystal.

Quasi-Two-Dimensional h-BN/β-GaO Heterostructure Metal-Insulator-Semiconductor Field-Effect Transistor.

β-gallium oxide (β-GaO) and hexagonal boron nitride (h-BN) heterostructure-based quasi-two-dimensional metal-insulator-semiconductor field-effect transistors (MISFETs) were demonstrated by integrating mechanical exfoliation of (quasi)-two-dimensional materials with a dry transfer process, wherein nanothin flakes of β-GaO and h-BN were utilized as the channel and gate dielectric, respectively, of the MISFET. The h-BN dielectric, which has an extraordinarily flat and clean surface, provides a minimal density of charged impurities on the interface between β-GaO and h-BN, resulting in superior device performances (maximum transconductance, on/off ratio, subthreshold swing, and threshold voltage) compared to those of the conventional back-gated configurations. Also, double-gating of the fabricated device was demonstrated by biasing both top and bottom gates, achieving the modulation of the threshold voltage.

Exfoliated β-Ga2O3 nano-belt field-effect transistors for air-stable high power and high temperature electronics.

This study demonstrated the exfoliation of a two-dimensional (2D) β-Ga2O3 nano-belt and subsequent processing into a thin film transistor structure. This mechanical exfoliation and transfer method produces β-Ga2O3 nano-belts with a pristine surface as well as a continuous defect-free interface with the SiO2/Si substrate. This β-Ga2O3 nano-belt based transistor displayed an on/off ratio that increased from approximately 10(4) to 10(7) over the operating temperature range of 20 °C to 250 °C.