Band engineering using the van der Waals heterostructure of two-dimensional materials allows for the realization of high-performance optoelectronic devices by providing an ultrathin and uniform PN junction with sharp band edges. In this study, a highly sensitive photodetector based on the van der Waals heterostructure of WSe 2 and MoS 2 was developed. The MoS 2 was utilized as the channel for a phototransistor, whereas the WSe 2 −MoS 2 PN junction in the out-of-plane orientation was utilized as a charge transfer layer. The vertical built-in electric field in the PN junction separated the photogenerated carriers, thus leading to a high photoconductive gain of 10 6 . The proposed phototransistor exhibited an excellent performance, namely, a high photoresponsivity of 2700 A/W, specific detectivity of 5 × 10 11 Jones, and response time of 17 ms. The proposed scheme in conjunction with the largearea synthesis technology of two-dimensional materials contributes significantly to practical photodetector applications.

Low-power, nonvolatile memory is an essential electronic component to store and process the unprecedented data flood arising from the oncoming Internet of Things era. Molybdenum disulfide (MoS 2 ) is a 2D material that is increasingly regarded as a promising semiconductor material in electronic device applications because of its unique physical characteristics. However, dielectric formation of an ultrathin low-k tunneling on the dangling bond-free surface of MoS 2 is a challenging task. Here, MoS 2 -based low-power nonvolatile charge storage memory devices are reported with a poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane) (pV3D3) tunneling dielectric layer formed via a solvent-free initiated chemical vapor deposition (iCVD) process. The surface-growing polymerization and low-temperature nature of the iCVD process enable the conformal growing of low-k (≈2.2) pV3D3 insulating films on MoS 2 . The fabricated memory devices exhibit a tunable memory window with high on/off ratio (≈10 6 ), excellent retention times of 10 5 s with an extrapolated time of possibly years, and an excellent cycling endurance of more than 10 3 cycles, which are much higher than those reported previously for MoS 2based memory devices. By leveraging the inherent flexibility of both MoS 2 and polymer dielectric films, this research presents an important milestone in the development of low-power flexible nonvolatile memory devices.

In this study, we propose the fabrication of a photodetector based on the heterostructure of p-type Si and n-type MoS 2 . Mechanically exfoliated MoS 2 flakes are transferred onto a Si layer; the resulting Si−MoS 2 p−n photodiode shows excellent performance with a responsivity (R) and detectivity (D*) of 76.1 A/ W and 10 12 Jones, respectively. In addition, the effect of the thickness of the depletion layer of the Si−MoS 2 heterojunction on performance is investigated using the depletion layer model; based on the obtained results, we optimize the photoresponse of the device by varying the MoS 2 thickness. Furthermore, low-frequency noise measurement is performed for the fabricated devices. The optimized device shows a low noise equivalent power (NEP) of 7.82 × 10 −15 W Hz −1/2 . Therefore, our proposed device could be utilized for various optoelectronic devices for low-light detection.

Two-dimensional (2D) materials have attracted significant attention because of their outstanding electrical, mechanical, and optical characteristics. Because all of the conducting (graphene), semiconducting (molybdenum disulfide, MoS 2 ), and insulating (hexagonal boron nitride, h-BN) components can be constructed from 2D materials, thin-film transistors based on 2D materials (2D TFTs) have been developed. However, scaling-up is necessary for these technologies to go beyond their initial implementation using the mechanical exfoliation method. Furthermore, it would be beneficial to find a method to realize high flexibility and/or transparency to their full potential. In this study, large-scale, flexible, and transparent 2D TFTs are developed and demonstrated as a backplane in active-matrix organic light-emitting diodes (AMOLEDs). With the optical chemical vapor deposition of the 2D materials, flexible (bending radius < 1 mm) and transparent (transmittance > 70%) TFTs with high electrical performances (mobility ≈ 10 cm 2 V −1 s −1 , on/off current ratio > 10 6 ) can be achieved. Furthermore, 2D TFTs are integrated into OLEDs by connecting the source electrode of the TFT to the anode of the OLED via a single graphene film, thus demonstrating pixel-by-pixel driving through a 2D TFT array in an active-matrix configuration.

2D‐layered transition metal dichalcogenides (TMDCs) such as molybdenum disulfide (MoS2) are promising materials for next‐generation active matrix organic light‐emitting diode (AMOLED) display technology owing to their high mobility and large bandgap size. However, practical applications of TMDCs in driving circuits for flexible displays remain challenging because of the lack of high‐quality large‐area thin films and suitable fabrication processes. Here, millimeter‐scale large‐area bilayer or trilayer MoS2 thin films are synthesized through chemical vapor deposition (CVD) and an AMOLED driver circuit array consisting of bottom‐gate staggered CVD‐grown MoS2 thin‐film transistors is fabricated on a flexible polyimide substrate. The flexible driver circuit exhibits a stable switching and driving operation under tensile strain induced by a bending radius of 3.5 mm, showing field‐effect mobilities of up to ≈9 cm2 V−1 s−1, large ON‐state current density (up to ≈5 µA µm−1), and high ON/OFF‐state drain current ratio (maximum value of over 108) with an operating gate voltage below 10 V. The results demonstrate that MoS2 backplanes are among the promising candidates for next‐generation deformable and transparent AMOLED displays.