Super-Stable High-Quality Few-Layer Black Phosphorus for Photonic Applications

Few-layer black phosphorus (BP) is one of the most important 2D materials due to its strongly layer-dependent quantized band structure, which leads to wavelength tunable emission and absorption properties. Such properties are essential for a variety of photonic device applications such as lasers, detectors, and modulators in a wide range of near-infrared wavelengths. However, the material quality and stability have become a bottleneck along with other challenges such as poor light emission properties and considerable uncertainty of basic material parameters. In this paper, we developed a systematic strategy for preparing high-quality stable few-layer BP samples by combining O2 plasma etching, boron nitride sandwiching, and subsequent thermal annealing. Our strategy has successfully produced few-layer BP samples with a record-long lifetime, with 80% of photoluminescence intensity remaining after 7 months. Importantly, we found that lattice reconstruction and reparation of oxidized BP surfaces increased BP thickness by one monolayer, leading to the restoration of BP crystal structure, improved material quality and stability, and restoration of intrinsic optical properties. As a result, 200× PL enhancement and 2× line width reduction are achieved, allowing the establishment of a more definite relationship between the layer number and PL energies for the first time. Our results could help unleash the full potential of few-layer BP in photonics applications in a wide range of near-infrared wavelengths.