Cd Doping Induced Giant Bulk Photovoltaic Effect in Noncentrosymmetric InSe via Shift Current Mechanism

ABSTRACT The pursuit of high‐performance bulk photovoltaic (BPV) materials beyond the limitations of conventional ferroelectrics and low‐dimensional semiconductors remains a significant challenge. A breakthrough via cadmium (Cd) doping in the layered semiconductor indium selenide (InSe) is demonstrated, which enables a synergistic modulation of electrical and photovoltaic properties. Comprehensive characterization confirms the noncentrosymmetric ε‐phase structure of the synthesized Cd‐InSe crystals and the effective incorporation of Cd atoms. Electrical measurements reveal a stable transition from intrinsic n ‐type to p ‐type conduction upon Cd doping, with a superior gate‐tunable on/off ratio of ≈3 × 10 4 . Leveraging its strong optical transition probability and noncentrosymmetric structure, Cd‐InSe exhibits a pronounced bulk photovoltaic effect (BPVE), achieving record‐high BPV coefficients, which is up to 20 times greater than the best van der Waals systems. Combined experimental and theoretical investigations elucidate that the observed BPVE is primarily governed by a shift current mechanism originating from the in‐plane structural anisotropy and the resonant absorption due to interband transitions generated by the shallow valence band states modified by Cd doping. This study establishes elemental doping in layered materials as a powerful strategy for co‐designing carrier polarity and BPV optoelectronic response, paving the way for advanced self‐powered and polarization‐sensitive photonic devices.