Mechanochemistry of Phosphorus and Arsenic Alloys for Visible and Infrared Photonics

Abstract

2D black phosphorus–arsenic (PA) alloys are produced by mechanochemistry using a high‐energy planetary ball mill. Conversion sequence starts with alloying of elemental red phosphorus with elemental arsenic into trigonal PA phase followed by phase transformation into orthorhombic PAs. Exfoliated few‐layer solutions exhibit optical gaps near ≈1.9 eV, indicating that these alloys are suitable for visible and near‐infrared photonic applications. Incorporating few‐layer 2D phosphorus–arsenic alloys (PAs) into optoelectronic devices requires a synthesis technique that allows control of the alloy composition while producing volumes of material suitable for application development such as photodetectors, solar cells, and lasers. With that goal in mind, high‐energy ball milling allows production of both orthorhombic (o‐PAs) and trigonal (t‐PAs) alloys by reacting red phosphorus and metallic arsenic powders. The synthesis follows a two‐step process in which arsenic rapidly reacts with red phosphorus to first produce t‐PAs followed by a slower phase transformation into o‐PAs; synthesis time and overall conversion rate are slightly enhanced by the presence of arsenic. Optical measurements on exfoliated alloys at the few‐layer atomic limit of the 2D PAs reveal emission spanning from the visible (≈1.9 eV) into the near‐infrared region, covering a broad application space. Rapid powder synthesis within a closed system for stochiometric control of the solid‐solution PAs alloys combined with solution‐based exfoliation opens up opportunities for a whole new class of optoelectronic devices based on PA nanomaterials.