Band-Edge Mixture\nEngineered Giant and Switchable\nShift Current Generation

Two-dimensional materials have enormous development prospects\nin\nthe bulk photovoltaic effect (BPVE). The enhancement and manipulation\nof the BPVE are some of the key roles of its various applications.\nThrough a simplified Hamiltonian model, this work shows that a substantial\nband mixture between occupied and unoccupied states could produce\na large optical absorption rate with trivial topological features,\nresulting in a significantly enhanced shift current generation. Furthermore,\nthis mechanism is illustrated in a realistic C<sub>3</sub>B/C<sub>3</sub>N bilayer material based on density functional theory calculation\nand tight-binding model. As each layer of C<sub>3</sub>B/C<sub>3</sub>N is centrosymmetric, the in-plane shift current arises from the\ninterfacial interaction. The electron transfer between the layers\ngives a controllable band mixture, which offers a giant shift current\nreaching over ∼1500 μA/V<sup>2</sup>. In addition, we\npropose that interlayer sliding could reverse the in-plane shift current.\nOur work suggests a feasible approach for giant and switchable nonlinear\noptical processes.