  Recently, intriguing physical properties have been unraveled in anisotropic
layered semiconductors, in which the in-plane electronic band structure
anisotropy often originates from the low crystallographic symmetry and thus a
thickness-independent character emerges. Here, we apply high-resolution
angle-resolved photoemission spectroscopy to directly image the in-plane
anisotropic energy bands in monoclinic gallium telluride (GaTe). Our
first-principles calculations reveal the in-plane anisotropic energy band
structure of GaTe measured experimentally is dominated by a strong bulk-surface
interaction rather than geometric factors, surface effect and quantum
confinement effect. Furthermore, accompanied by the thickness of GaTe
increasing from mono- to few-layers, the strong interlayer coupling of GaTe
induces direct-indirect-direct band gap transitions and the in-plane anisotropy
of hole effective mass is reversed. Our results shed light on the physical
origins of in-plane anisotropy of electronic structure in GaTe, paving the way
for the design and device applications of nanoelectronics and optoelectronics
based on anisotropic layered semiconductors.
