Growth and Simultaneous Valleys Manipulation of Two-Dimensional MoSe₂-WSe₂ Lateral Heterostructure.

Abstract

The covalently bonded in-plane heterostructure (HS) of monolayer transition-metal dichalcogenides (TMDCs) possesses huge potential for high-speed electronic devices in terms of valleytronics. In this study, high-quality monolayer MoSe₂-WSe₂ lateral HSs are grown by pulsed-laser-deposition-assisted selenization method. The sharp interface of the lateral HS is verified by morphological and optical characterizations. Intriguingly, photoluminescence spectra acquired from the interface show rather clear signatures of pristine MoSe₂ and WSe₂ with no intermediate energy peak related to intralayer excitonic matter or formation of Mo_xW_(1-x)Se₂ alloys, thereby confirming the sharp interface. Furthermore, the discrete nature of laterally attached TMDC monolayers, each with doubly degenerated but nonequivalent energy valleys marked by (K_M, K'_M) for MoSe₂ and (K_W, K'_W) for WSe₂ in k space, allows simultaneous control of the four valleys within the excitation area without any crosstalk effect over the interface. As an example, K_M and K_W valleys or K'_M and K'_W valleys are simultaneously polarized by controlling the helicity of circularly polarized optical pumping, where the maximum degree of polarization is achieved at their respective band edges. The current work provides the growth mechanism of laterally sharp HSs and highlights their potential use in valleytronics.