Highly anisotropic electronic transport properties of monolayer and   bilayer phosphorene from first principles
  The intrinsic carrier transport dynamics in phosphorene is theoretically examined. Utilizing a density functional theory treatment, the low-field mobility and the saturation velocity are characterized for both electrons and holes in the monolayer and bilayer structures. The analysis clearly elucidates the crystal orientation dependence manifested through the anisotropic band structure and the carrier-phonon scattering rates. In the monolayer, the hole mobility in the armchair direction is estimated to be approximately five times larger than in the zigzag direction at room temperature (460 cm$^2$/Vs vs. 90 cm$^2$/Vs). The bilayer transport, on the other hand, exhibits a more modest anisotropy with substantially higher mobilities (1610 cm$^2$/Vs and 760 cm$^2$/Vs, respectively). The calculations on the conduction-band electrons indicate a comparable dependence while the characteristic values are generally smaller by about a factor of two. The variation in the saturation velocity is found to be less pronounced. With the anticipated superior performance and the diminished anisotropy, few-layer phosphorene offers a promising opportunity particularly in p-type applications. 
Zhenghe Jin, Jeffrey T. Mullen, Ki Wook Kim
cond-mat.mes-hall