Defect-Free Sb-Doping in Bi2O2Se Achieves Two-Order-of-Magnitude Reduction in Saturation Intensity While Preserving High Carrier Mobility.

Doping generally introduces performance trade-offs in materials, yet overcoming this fundamental limitation remains crucial for advancing materials research. Bi2O2Se exhibits exceptional electronic properties as a promising semiconductor, yet its nonlinear optical response under low excitation intensities hinders its practical applications. Therefore, precise Sb3⁺ doping in Bi2O2Se (Bi1.9Sb0.1O2Se) is achieved for the first time via solid-state reaction and systematically studies its impact on the electronic structure and optical properties through first-principles calculations and experimental. The results reveal that Sb3⁺ substitution slightly reduces the bandgap without introducing defect states, and transient absorption spectroscopy further confirms prolonged carrier relaxation. At 1.5 µm, the modulation depth from 8.8% to 10.1% while dramatically reducing the saturation intensity from 47.2 to 0.53 kW cm- 2. This improvement is attributed to the stable linear absorption characteristics after doping, the synergistic effect between prolonged relaxation time and free-carrier-induced optical loss. In a mode-locking system, Bi1.9Sb0.1O2Se achieves a broader 3-dB and shorter pulse duration at substantially reduced pump intensities. This work achieves defect-free energy level optimization in Sb-doped Bi2O2Se, where the material's high carrier mobility is not only preserved but further enhanced, while the saturation intensity is declined by about two orders of magnitude, enabling a low-power, high-performance nonlinear photonic devices.