Graphene subject to a spatially uniform, circularly-polarized electric field supports a Floquet spectrum with properties akin to those of a topological insulator, including non-vanishing Chern numbers associated with bulk bands and current-carrying edge states. Transport properties of this system however are complicated by the non-equilibrium occupations of the Floquet states. We address this by considering transport in a two-terminal ribbon geometry for which the leads have well-defined chemical potentials, with an irradiated central scattering region. We demonstrate the presence of edge states, which for infinite mass boundary conditions may be associated with only one of the two valleys. At low frequencies, the bulk DC conductivity near zero energy is shown to be dominated by a series of states with very narrow anticrossings, leading to super-diffusive behavior. For very long ribbons, a ballistic regime emerges in which edge state transport dominates.

Bias temperature stresses (BTSs) are critical factors that cause severe threshold voltage (V th ) instability in silicon carbide (SiC) metal-oxide-semiconductor (MOS) devices. In this work, we studied the behavior of flatband voltage (V fb ) instability in 4H-SiC MOS capacitors under various BTSs from low temperature (LT) to high temperature (HT) considering the combined effects of interfacial traps and mobile ions. Results showed that nitrogen and nitrogen-hydrogen plasma passivation improved the V fb instability. The initial sweeping gate voltage determined the direction of V fb shift. BTSs from LT to HT induced different capacitance-voltage hysteresis characteristics. The V fb shift was further separated according to the contribution of the interface trapped, oxide trapped, and mobile ionic charges. At LT, the charge trapping dominated the shift behavior. The interface trap density was also extracted by another high-frequency and quasi-static method, which was the same as the separated interface trap density at 100 K, confirming the separation correctness of V fb shift. At room temperature, charge trapping and mobile ions with very weak mobility contributed to the V fb shift. At HT, mobile ions that counteracted the charge-trapping effect determined the V fb shift, although the additional traps were activated in the interface and oxide. Physical models of V fb instability under different temperature stresses were proposed. Finally, we chose the 100 K, 273 K, and 423 K to analyze gate bias stresses and stress time induced V fb instabilities as well as their mechanisms.

Substantial progress has been made in the experimental synthesis of large-area two-dimensional transition metal dichalcogenide (TMD) thin films in recent years. This has provided a solid basis to build non-planar structures to implement the unique electrical and mechanical properties of TMDs in various nanoelectronic and mechano-electric devices, which, however, has not yet been fully explored. In this work, we demonstrate the fabrication and characterization of MoS2 field-effect transistors (FETs) with an omega (Ω)-shaped gate. The FET is built based on the SiO2/MoS2 core–shell heterostructure integrated using atomic layer deposition (ALD) technique. The MoS2 thin film has been uniformly deposited by ALD as wrapping the SiO2 nanowire forming the channel region, which is further surrounded by the gate dielectric and the Ω-gate. The device has exhibited n-type behavior with effective switching comparable to the reference device with a planar MoS2 channel built on a SiO2/Si substrate. Our work opens up an attractive avenue to realize novel device structures utilizing synthetic TMDs, thereby broadening their potential application in future advanced nanoelectronics.

The fast-developing information technology has imposed urgent need for effective solutions to overcome the increasing power density in further scaled electronic devices and systems. The tunnel field-effect transistor (TFET) built with two-dimensional (2D) semiconductors has been widely studied due to its steep-slope switching capability with ultrathin channel. In this work, a symmetric TFET has been fabricated using the MoS 2 /black phosphorus/MoS 2 heterostructure as the channel material. The TFET device exhibits bidirectional current flow which is distinguished from the conventional asymmetric TFET geometry. Upon the application of top gate structure, the devices show sharp turn-on behavior which originated from the transport properties based on the band-to-band tunneling (BTBT) mechanism. By engineering of the top gate materials, a subthermionic subthreshold slope (SS) below 60 mV/dec at room temperature has been achieved, offering a new pathway to lower the power supply and power density in future integrated circuits based on novel 2D materials.

Two-dimensional (2D) materials have attracted much attention for their layered structures and diversity in electronic and optical properties. Sapphire and Si/SiO 2 were the most common substrates for chemically synthesized MoS 2 . Here, we demonstrated high-quality largescale MoS 2 film grown by atomic layer deposition (ALD) on an Fe-doped free-standing GaN substrate. In addition, we fabricated excellent performance and highly uniform top-gate FETs based on MoS 2 , and the average electron mobility of MoS 2 FETs was up to 3.54 cm 2 V −1 s −1 . Furthermore, Al 2 O 3 was introduced to act as a hard mask to prevent direct contact of photoresist and MoS 2 , which was compatible for the fabrication process and ensured the homogeneity of electrical properties of each FET. Our work paves a new way for chemically synthesized wafer-scale MoS 2 film, and it is promising to build large-scale integrated circuits other than FETs on a GaN substrate.