Exceptionally high hole mobilities in monolayer group-IV monochalcogenides GeTe and SnTe

Two-dimensional semiconductors are considered as promising channel materials for next-generation nanoelectronics devices, while their practical applications are typically limited by their low mobilities. In this work, using first-principles calculations combined with the Boltzmann transport formalism involving electron-phonon coupling, we study the transport properties of monolayer group-IV monochalcogenides (MX, M = Ge, Sn; X = S, Se, and Te). We find that the GeTe and SnTe possess exceptionally high hole mobilities, which even reach 835 and 1383 cm(2)/V s, respectively, at room temperature. More interestingly, the hole mobilities increase with the increase in the atomic number of "X" in MXs when "M" remains the same. Such a trend is mainly due to the increased group velocity and decreased density of states, and the latter plays a significant role in determining the carrier scattering space and relaxation time. Meanwhile, different from the acoustic deformation potential theory, we find that the high-energy optical phonons contribute a lot to the scattering. Our work shows that the monolayer GeTe and SnTe are promising p-type semiconductors in nanoelectronics and reveals the intrinsic connection between phonons, charge density of states, and mobility, which would shed light on exploring the two-dimensional materials with high mobility.