Direct observation of highly anisotropic electronic and optical nature in indium telluride

Metal monochalcogenides $(MX,$ $M=\mathrm{Ga}, \mathrm{In}; X=\mathrm{S}, \mathrm{Se}, \mathrm{Te})$ offer a large variety of electronic properties depending on chemical composition, number of layers, and stacking order. InTe material has a one-dimensional chain structure, from which intriguing properties arise. Precise experimental determination of the electronic structure of InTe is needed for a better understanding of potential properties and device applications. In this study, by combining angle-resolved photoemission spectroscopy and density functional theory calculations, we demonstrate the stability of InTe in the tetragonal crystal structure, with a semiconducting character and an intrinsic $p$-type doping. The valence band maximum results in being located at the high symmetric $M$ point with a high elliptical valley, manifesting a large effective mass close to the Fermi level. The longitudinal and transverse effective masses of the $M$ valley are measured as 0.2 ${m}_{0}$ and 2 ${m}_{0}$, respectively. More specifically, we observe that the effective mass of the hole carriers is about ten times larger along the chain direction compared to the perpendicular one. Remarkably, the in-plane anisotropy of effective mass from the experiment and in theoretical calculations are in good agreement. These observations indicate a highly anisotropic character of the electronic band structure, making InTe of interest for electronic and thermoelectric applications.