Rashba-type spin splitting and transport properties of novel Janus XWGeN2 (X = O, S, Se, Te) monolayers

Abstract

We discuss and examine the stability, electronic properties, and transport characteristics of asymmetric monolayers XWGeN₂ (X = O, S, Se, Te) using ab initio density functional theory. All four monolayers of quintuple-layer atomic Janus XWGeN₂ are predicted to be stable and they are all indirect semiconductors in the ground state. When the spin–orbit coupling (SOC) is included, a large spin splitting at the K point is found in XWGeN₂ monolayers, particularly, a giant Rashba-type spin splitting is observed around the Γ point in three structures SWGeN₂, SeWGeN₂, and TeWGeN₂. The Rashba parameters in these structures are directionally isotropic along the high-symmetry directions Γ–K and Γ–M and the Rashba constant α_R increases as the X element moves from S to Te. TeWGeN₂ has the largest Rashba energy up to 37.4 meV (36.6 meV) in the Γ–K (Γ–M) direction. Via the deformation potential method, we calculate the carrier mobility of all four XWGeN₂ monolayers. It is found that the electron mobilities of OWGeN₂ and SWGeN₂ monolayers exceed 200 cm² V⁻¹ s⁻¹, which are suitable for applications in nanoelectronic devices.