Engineering Angle-Dependent Interfacial Charge Transfer in SnS/WSe2 van der Waals Heterostructures

초록

Two-dimensional (2D) van der Waals (vdW) heterostructures (HSs) provide a versatile platforms for next-generation optoelectronic devices by integrating dissimilar materials without lattice-mismatching constraints [1, 2]. In particular, controlling interfacial properties is essential to tailor charge transfer processes, including the manipulation of valley degrees of freedom for valleytronics [3, 4]. In this study, we explore the angle-dependent interfacial charge transfer in vdW HSs composed of tin sulfide (SnS) and tungsten diselenide (WSe2), fabricated via two distinct methods: (1) direct epitaxial growth of SnS on WSe2 through a two-step process, and (2) mechanical transfer of pre-grown SnS onto WSe2. Density functional theory (DFT) calculations suggest that the direct epitaxy process favors a specific rotational alignment between SnS and WSe2, driven by interfacial energy minimization. Comparative photoluminescence (PL) measurements reveal that this rotational alignment critically influences charge transfer characteristics at the interface. Specifically, aligned HSs exhibit enhanced PL emission associated with the X-valley of SnS, whereas misaligned HSs show pronounced quenching of Y-valley emission. These observations suggest that the interfacial band structure?and consequently the valley-dependent carrier dynamics of SnS?is strongly modulated by its rotational alignment with WSe2. These findings demonstrate angular control as a powerful strategy for valley-selective band alignment engineering in vdW HSs, offering new opportunities for designing advanced optoelectronic and valleytronic devices with tailored interfacial functionalities.