  Recently, emerging intriguing physical properties have been unraveled in
anisotropic layered semiconductors, with their in-plane anisotropy often
originated directly from the low crystallographic symmetry. However, little has
been known in the case where interlayer couplings dominate the anisotropy of
electronic band structures in them. Here, by both experiment and theory, we
show rather than geometric factors, the anisotropic energy bands of monoclinic
gallium telluride (GaTe) are determined by a subtle bulk-surface interaction.
Bulk electronic states are found to be the major contribution of the highest
valence band, whose anisotropy is yet immune to surface doping of potassium
atoms. The above peculiar behaviors are attributed to strong interlayer
couplings, which gives rise to an inverse of anisotropy of hole effective
masses and a direct-indirect-direct transition of band gap, depending on the
number of layers. Our results thus pave the way for future applications of
anisotropic layered semiconductors in nanoelectronics and optoelectronics.
