  We study the anisotropic electronic properties of 2D SnS, an analogue of
phosphorene, grown by physical vapor transport. With transmission electron
microscope and polarized Raman spectroscopy, we identify the zigzag and
armchair directions of the as-grown 2D crystals. 2D SnS field-effect
transistors with a cross-Hall-bar structure are fabricated. They show heavily
hole-doped (~10$^{19}$ cm$^{-3}$) conductivity with strong in-plane anisotropy.
At room temperature the mobility along the zigzag direction exceeds 20
cm$^{2}$V$^{-1}$s$^{-1}$, which can be up to 1.7 times of that in the armchair
direction. This strong anisotropy is then explained by the effective-mass ratio
along the two directions and agrees well with previous theoretical predictions.
Temperature-dependent carrier density is used to find out the acceptor energy
level to be ~45 meV above the valence band maximum. This value matches with a
calculated defect level of 42 meV for Sn vacancies, indicating that Sn
deficiency is the main cause of the p-type conductivity.
