  The carrier mobility of anisotropic two-dimensional (2D) semiconductors under
longitudinal acoustic (LA) phonon scattering was theoretically studied with the
deformation potential theory. Based on Boltzmann equation with relaxation time
approximation, an analytic formula of intrinsic anisotropic mobility was
deduced, which shows that the influence of effective mass to the mobility
anisotropy is larger than that of deformation potential constant and elastic
modulus. Parameters were collected for various anisotropic 2D materials (black
phosphorus, Hittorf's phosphorus, BC$_2$N, MXene, TiS$_3$, GeCH$_3$) to
calculate their mobility anisotropy. It was revealed that the anisotropic ratio
was overestimated in the past.
