Growth of vertical heterostructures based on orthorhombic SnSe/hexagonal In₂Se₃ for high-performance photodetectors

Vertical heterostructures based on two-dimensional (2D) layered materials are ideal platforms for electronic structure engineering and novel device applications. However, most of the current heterostructures focus on layered crystals with a similar lattice. In addition, the heterostructures made by 2D materials with different structures are rarely investigated. In this study, we successfully fabricated vertical heterostructures by combining orthorhombic SnSe/hexagonal In₂Se₃ vertical heterostructures using a two-step physical vapor deposition (PVD) method. Structural characterization reveals that the heterostructures are formed of vertically stacked SnSe on the top of the In₂Se₃ film, and vertical heterostructures possess high quality, where In₂Se₃ exposed surface is the (0001) plane and SnSe prefers growing along the [100] direction. Raman maps confirm the precise spatial modulation of the as-grown SnSe/In₂Se₃ heterostructures. In addition, high-performance photodetectors based on the vertical heterostructures were fabricated directly on the substrate, which showed a broadband response, reversibility and stability. Compared with the dark current, the device demonstrated one order magnification of photocurrent, about 186 nA, under 405 nm laser illumination and power of 1.5 mW. Moreover, the device shows an obvious increase in the photocurrent intensity with the changing incident laser power, where I _ph ∝ P ^0.7. Also, the device demonstrated a high responsivity of up to 350 mA W^-1 and a fast response time of about 139 ms. This study broadens the horizon for the synthesis and application of vertical heterostructures based on 2D layered materials with different structures and further develops exciting technologies beyond the reach of the existing materials.