One-pot Liquid-Phase Synthesis of MoS$_2$-WS$_2$ van der Waals Heterostructures for Broadband Photodetection

Abstract: Two dimensional (2D) van der Waals heterostructures (vdWHs) have their unique potential in facilitating the stacking of layers of different 2D materials for optoelectronic devices with superior characteristics at a reduced cost. However, the fabrication of large area all-2D heterostructures is still challenging towards realizing practical devices. In the present work, we have demonstrated a rapid yet simple, impurity free and highly efficient sonication-assisted chemical exfoliation approach to synthesize hybrid vdWHs based on 2D molybdenum disulphide (MoS$_2$) and tungsten disulphide (WS$_2$), with high yield. Microscopic and spectroscopic studies have confirmed the successful exfoliation of layered 2D materials and formation of their hybrid heterostructure. The co-existence of 2D MoS2 and WS2 in the vdW hybrid is established by optical absorption and Raman shift measurements along with their chemical stiochiometry determined by X-ray photoelectron spectroscopy. The spectral response of the vdWH/Si (2D/3D) heterojunction photodetector fabricated using the as-synthesized material is found to show superior broadband photoresponse compared to that shown by the individual 2D MoS$_2$ and WS$_2$ based devices. The peak responsivity is found to be ~2.15 A/W at a wavelength of ~560 nm for an applied bias of -5 V. The ease of fabrication and superior performance of the chemically synthesized vdWH-based devices have revealed their potential use for large area optoelectronic applications on Si compatible CMOS platforms.