Through the stacking technique of 2D materials, the interfacial polarization can be switched by an interlayer sliding, known as sliding ferroelectricity, which is advantageous in ultra-thin thickness, high switching speed, and high fatigue resistance. However, uncovering the relationship between the sliding path and the polarization state in rhombohedral-stacked materials remains a challenge, which is the key to 2D sliding ferroelectricity. Here, layer-dependent multidirectional sliding ferroelectricity in rhombohedral-stacked InSe (γ-InSe) is reported via dual-frequency resonance tracking piezoresponse force microscopy and conductive atomic force microscopy. The graphene/γ-InSe/graphene tunneling device exhibits a tunable bulk photovoltaic effect with a photovoltaic current density of ≈15 mA cm-2 due to multiple polarization states. The generation of dome-like domain walls is observed experimentally, which is attributed to the multidirectional sliding-induced domains based on the theoretical calculations. Furthermore, the ferroelectric polarization in γ-InSe ensures that the tunneling device has a high photo responsivity of ≈255 A W-1 and a fast response time for real-time imaging. The work not only provides insights into the multidirectional sliding ferroelectricity of rhombohedral-stacked 2D materials but also highlights their potential for tunable photovoltaics and imaging applications.
Keywords: 2D materials; bulk photovoltaic effect; photodetection; sliding ferroelectricity; van der Waals heterostructures; γ‐InSe.
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