Rashba-type spin splitting and transport properties of novel Janus XWGeN 2 (X = O, S, Se, Te) monolayers.

We discuss and examine the stability, electronic properties, and transport characteristics of asymmetric monolayers XWGeN 2 (X = O, S, Se, Te) using ab initio density functional theory. All four monolayers of quintuple-layer atomic Janus XWGeN 2 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 XWGeN 2 monolayers, particularly, a giant Rashba-type spin splitting is observed around the Γ point in three structures SWGeN 2 , SeWGeN 2 , and TeWGeN 2 . 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. TeWGeN 2 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 XWGeN 2 monolayers. It is found that the electron mobilities of OWGeN 2 and SWGeN 2 monolayers exceed 200 cm 2 V -1 s -1 , which are suitable for applications in nanoelectronic devices.