Few-layer selenium-doped black phosphorus: synthesis, nonlinear optical properties and ultrafast photonics applications

We reported on the synthesis of high quality bulk selenium (Se)-doped black phosphorus (BP) crystals using a mineralizer assisted gas-phase transformation in a mild growth condition and employed a liquid phase exfoliation approach to obtain few-layer (FL) Se-doped BP nano-sheets from the bulk counterpart. We experimentally found that FL Se-doped BP shows enhanced optical saturable absorption with long term stability, which may originate from selenium doping-induced changes of intrinsic carrier density. Taking advantage of its nonlinear optical property, we designed an optical saturable absorber (SA) device based on FL Se-doped BP, allowing the generation of a femto-second pulse in the fiber laser. Our results not only provide a new strategy in tailoring the nonlinear optical response of BP through element doping, but also suggest that FL Se-doped BP can be developed as a excellent candidate for ultrafast photonics.