Band-Edge Mixture Engineered Giant and Switchable Shift Current Generation

Two-dimensional materials have enormous development prospects in the bulk photovoltaic effect (BPVE). The enhancement and manipulation of the BPVE are some of the key roles of its various applications. Through a simplified Hamiltonian model, this work shows that a substantial band mixture between occupied and unoccupied states could produce a large optical absorption rate with trivial topological features, resulting in a significantly enhanced shift current generation. Furthermore, this mechanism is illustrated in a realistic C₃B/C₃N bilayer material based on density functional theory calculation and tight-binding model. As each layer of C₃B/C₃N is centrosymmetric, the in-plane shift current arises from the interfacial interaction. The electron transfer between the layers gives a controllable band mixture, which offers a giant shift current reaching over ∼1500 μA/V². In addition, we propose that interlayer sliding could reverse the in-plane shift current. Our work suggests a feasible approach for giant and switchable nonlinear optical processes.