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

## TL;DR

This paper shows that antimony doping in a semiconductor material improves its performance by reducing the energy needed for operation while keeping high electron mobility.

## Contribution

The study achieves defect-free Sb³⁺ doping in Bi₂O₂Se, significantly reducing saturation intensity without compromising carrier mobility.

## Key findings

- Sb³⁺ doping reduces saturation intensity by two orders of magnitude while preserving high carrier mobility.
- Doping prolongs carrier relaxation and enhances nonlinear optical response in Bi₂O₂Se.
- The material enables low-power, high-performance nonlinear photonic devices with broader bandwidth and shorter pulses.

## Abstract

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.

This study demonstrates defect‐free states Sb3⁺ doping in Bi2O2Se, enhancing carrier mobility while reducing saturation intensity by about two orders of magnitude. First‐principles calculations and experiments reveal optimized electronic structure and improved nonlinear response. The doped material enables low‐threshold mode‐locked lasers with broader bandwidth and shorter pulses, advancing energy‐efficient nonlinear photonic devices.