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Probing the Ultrafast Response of Atomically Thin Black Phosphorus

Bryan Berggren
Faculty mentors: Kehav (Okinawa Institute of Science and Technology), Chris Weber

Black phosphorus (BP) has recently emerged as a two-dimensional semiconductor with unique optical and electronic properties. Characteristics of few-layer BP in particular give the material potential for use in technological applications, but to realize BP’s potential, more needs to be understood about how its electrons behave during the first picoseconds after photo-excitation. In this work, we observe the emergence of a strong and fast nonlinear optical response in BP as we go from multilayer to bilayer samples. We determine that this response originates in electron-substrate interaction through Auger processes. A quantitative model based on defect-assisted Auger recombination accurately reproduces both thickness- and power- dependent results. Our results reveal the interactions that govern the electron dynamics of atomically thin BP, and suggest the possibility of engineering the optical response through interaction with the substrate. These results have significant implications in the development of BP-based technology, such as telecom devices, saturable absorbers or IR and THz detectors.