Light-Matter Interactions in Phosphorene.

Since the beginning of 2014, phosphorene, a monolayer or few-layer of black phosphorus, has been rediscovered as a two-dimensional (2D) thin film, revealing a plethora of properties different from the bulk material studied so far. Similar to graphene and transition metal dichalcogenides (TMDs), phosphorene is also a layered material that can be exfoliated to yield individual layers. It is one of the few monoelemental 2D crystals and the only one, besides graphene, known to be stable in monolayer, few layer, and bulk form. Recently the intensified research in phosphorene is motivated not only by the study of its fundamental physical properties in the 2D regime, such as tunable bandgap and anisotropic behavior, but also by the high carrier mobility and good on/off ratio of phosphorene-based device prototypes, making it a potential alternative for next generation nanooptoelectronics and nanophotonics applications in the "post-graphene age" The electronic bandgap of phosphorene changes from 0.3 eV in the bulk to 2.1 eV in monolayer. Thus, phosphorene exhibits strong light-matter interactions in the visible and infrared (IR) frequencies. In this Account, we present the progress on understanding the various interactions between light and phosphorene, giving insight into the mechanism of these interactions and the respective applications. We begin by discussing the fundamental optical properties of phosphorene, using theoretical calculations to depict the layer-dependent electronic band structures and anisotropic optical properties. Many-body effects in phosphorene, including excitons and trions and their binding energies and dynamics are reviewed as observed in experiments. For phosphorene, the fast degradation in ambient condition, caused by photoinduced oxidation, is considered as a longstanding challenge. In contrast, oxidation can be used to engineer the band structure of phosphorene and, in parallel, its optical properties. Based on the strong light-matter interactions, we introduce a controllable method to directly oxidize phosphorene by laser techniques. With the oxidization induced by laser scanning, localized bandgap engineering can be achieved and microphotonics are demonstrated on the oxidized phosphorene. Finally, we will present a brief discussion on the realization of phosphorene-based building blocks of optoelectronic devices. Naturally, the strong light-matter interactions in phosphorene could enable efficient photoelectric conversion in optoelectronic devices. We will describe high performance photodetectors based on phosphorene, and the working mechanism of those devices will be introduced. The photovoltaic effect could also be exhibited in phosphorene. This indicates the pervasive potential of phosphorene in nanooptoelectronics.