This study explored the development of polarity control for 2D transistors through the use of a metallic 2D material, chlorine-doped SnSe2 (Cl–SnSe2), as contact for WSe2 transistors. The use of Cl–SnSe2 was demonstrated to provide clean van der Waals contact, which leads to nearly ideal Schottky barrier heights, thus allowing for excellent control over the carrier polarity of the transistor. Finally, this ability to control the polarity enables the fabrication of functional logic gates and circuits, including inverter, NAND, and NOR. We also confirm that the applicability of our contact approach to other 2D material, MoS2, demonstrating generality of van der Waals contact strategy that could be used in pinning-free high-performance 2D electronics.

 This study is the first to demonstrate an asymmetric split-gate configuration, called the asymmetry field-effect phototransistor or AFEPT. Our structure allows for an effective modulation of the electric field profile throughout the channel as well as enhanced photocarrier transport, thereby providing a new platform for probing photocarrier dynamics in intrinsic 2D material layers. By controlling the electric field, we observe the spatial evolution of the photocurrent and find a strong signal over the entire channel (WSe2 in this work). Furthermore, we confirm the origin of the novel photocurrent behaviour using photocurrent and optical spectroscopy measurements, and also establish a room temperature exciton binding energy of 230 meV. 

 In this paper, we propose multilayered WSe2/MoS2 heterojunctions with periodically arrayed nanopore structures (PANS) in the active area for improving phototransistor efficiency. To understand the optical and optoelectronic properties of our novel heterojunction devices, we have performed density functional theory (DFT) calculations, photoluminescence (PL) and time-resolved photoluminescence (TR-PL) measurements, and device characterization. Through the DFT calculations and measured optical properties, an indirect to direct bandgap transition was clearly observed in the heterostructure devices with PANS, evidencing the creation of a new bandgap assisted by new defect states through the formation of PANS in the TMD materials. In addition, the device characteristics of heterojunction phototransistors with PANS reveal enhanced photodetector figures of merit compared with pristine heterojunction devices without PANS.

 The development of a multi-level memory device for multinary arithmetic computers has encountered challenges in achieving low-power, ultra-high-speed operation. Optical communication technology is thought to provide the best answer to the puzzle of effectively transferring huge amounts of data between arithmetic and storage devices. Here, by replicating a floating gate architecture with CdSe/ZnS type-I core/shell quantum dots, we demonstrate a 2D-0D hybrid optical multi-level memory device that is operated by laser pulses. Analysis of the developed device led to a new hypothesis that charge transfer is difficult for laterally adjacent quantum dots facing a double ZnS shell, which we test by separately stimulating different positions on the 2D-0D hybrid structure with finely focused laser pulses. Results indicate that each laser pulse induced independent multi-level memory characteristics in the 2D-0D hybrid architecture. Based on this phenomenon, we propose a multi-level memory inverter to produce multi-level memory effects, such as programming and erasing, solely through the use of laser pulses.