Band order reversal and valley engineering driving to dual high electron and hole mobility in strained monolayer BS

Strain engineering is an effective method to tune the physical properties of materials. In this work, we found that applying 5% biaxial compression to monolayer boron sulfur can simultaneously induce a band order reversal of valence bands and valley engineering of conduction bands. This change significantly enhances the room temperature intrinsic mobility, boosting it from 2 to 260 cm2 V−1 s−1 for holes and 63 to 543 cm2 V−1 s−1 for electrons. The high hole mobility surpasses that of bulk GaN and silicon. We further demonstrate that the valence band order reversal not only lifts the px/y state above the pz states, giving to a more dispersive highest valence band, and thus smaller electron scattering channels and hole effective mass, but also shifts the stronger σz bonding to weaker π-bonding characteristics, resulting in smaller electron–phonon coupling strength. Those combined effects results in a substantial increase in hole mobility.