Nitrophosphorene: A 2D Semiconductor with Both Large Direct Gap and Superior Mobility*

A new two-dimensional phosphorus nitride monolayer (P2₁/c-PN) with distinct structural and electronic properties is predicted based on first-principle calculations. The energy of this allotrope is slightly above the convex hull between black phosphorous and phosphorous nitride (P₃N₅) and is 46.4 meV/PN lower than the most stable phosphorus nitride allotropes in previous reports. Unlike pristine single-atom group V monolayers such as nitrogene, phosphorene, arsenene, and antimonene, P2₁/c-PN has an intrinsic direct band gap of 2.77 eV and remains as a direct gap semiconductor under compressive and tensile strains as large as 10%. Strikingly, P2₁/c-PN shows excellent electron mobility up to 290829.81 cm² V^-1s^-1 along a direction, which is about 18 times of that in monolayer black phosphorus, and electric transport also show high anisotropy. This put P2₁/c-PN way above the general relation that carrier mobility is inversely proportional to bandgap, making it a very unique two-dimensional material for nanoelectronics devices.