Electronic and Optoelectronic Monolayer WSe2 Devices via Transfer-Free Fabrication Method.

Monolayer transition metal dichalcogenides (TMDs) have drawn significant attention for their potential applications in electronics and optoelectronics. To achieve consistent electronic properties and high device yield, uniform large monolayer crystals are crucial. In this report, we describe the growth of high-quality and uniform monolayer WSe2 film using chemical vapor deposition on polycrystalline Au substrates. This method allows for the fabrication of continuous large-area WSe2 film with large-size domains. Additionally, a novel transfer-free method is used to fabricate field-effect transistors (FETs) based on the as-grown WSe2. The exceptional metal/semiconductor interfaces achieved through this fabrication method result in monolayer WSe2 FETs with extraordinary electrical performance comparable to those with thermal deposition electrodes, with a high mobility of up to ≈62.95 cm2 V-1 s-1 at room temperature. In addition, the as-fabricated transfer-free devices can maintain their original performance after weeks without obvious device decay. The transfer-free WSe2-based photodetectors exhibit prominent photoresponse with a high photoresponsivity of ~1.7 × 104 A W-1 at Vds = 1 V and Vg = -60 V and a maximum detectivity value of ~1.2 × 1013 Jones. Our study presents a robust pathway for the growth of high-quality monolayer TMDs thin films and large-scale device fabrication.

Selective Chemical Vapor Deposition Growth of WS2/MoS2 Vertical and Lateral Heterostructures on Gold Foils.

Vertical and lateral heterostructures consisting of atomically layered two-dimensional (2D) materials exhibit intriguing properties, such as efficient charge/energy transfer, high photoresponsivity, and enhanced photocatalytic activities. However, the controlled fabrication of vertical or lateral heterojunctions on metal substrates remains challenging. Herein, we report a facile and controllable method for selective growth of WS2/MoS2 vertical or lateral heterojunctions on polycrystalline gold (Au) foil by tuning the gas flow rate of hydrogen (H2). We find that lateral growth is favored without H2, whereas vertical growth mode can be switched on by introducing 8-10 sccm H2. In addition, the areal coverage of the WS2/MoS2 vertical heterostructures is tunable in the range of 12-25%. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) results demonstrate the quality and absence of cross-contamination of the as-grown heterostructures. Furthermore, we investigate the effects of the H2 flow rate on the morphology of the heterostructures. These pave the way to develop unprecedented 2D heterostructures towards applications in (opto)electronic devices.