Large and anisotropic carrier mobility in monolayers of the MA2Z4 series (M = Cr, Mo, W; A = Si, Ge; and Z = N, P)

The recent discovery of synthetic two-dimensional materials has opened up a new paradigm for exploring novel transport and optical properties, beyond those found in naturally occurring materials. Here, we present a detailed investigation of the acoustic phonon limited intrinsic carrier mobility in MA₂Z₄ series (M = Cr, Mo, W; A = Si, Ge; and Z = N, P) monolayers. We find that out of the twelve monolayers studied, only two are metallic (CrGe₂N₄ and CrGe₂P₄), and the rest of them are semiconducting. We demonstrate that the carrier mobilities in these monolayers are anisotropic and show a large variation, ranging from a small value of ∼90 cm² V^-1 s^-1 to a large value of ∼10⁴ cm² V^-1 s^-1. In addition, we show that strain engineering in these materials can further change the electronic band structure drastically, and change the carrier mobilities by up to a factor of 20. Our detailed and systematic study provides a useful platform for designing electronic devices based on the MA₂Z₄ family of materials.