Intrinsic defects and mid-gap states in quasi-one-dimensional indium telluride

Abstract

Recently, intriguing physical properties have been unraveled in anisotropic semiconductors in which the in-plane electronic band structure anisotropy often originates from the low crystallographic symmetry. The atomic chain is the ultimate limit in material downscaling for electronics—a frontier for establishing an entirely new field of one-dimensional quantum materials. Electronic and structural properties of chain-like InTe are essential for a better understanding of device applications such as thermoelectrics. Here, we use scanning tunneling microscopy/scanning tunneling spectroscopy (STS) measurements and density functional theory (DFT) calculations to image the in-plane structural anisotropy directly in tetragonal InTe. As results, we report the direct observation of one-dimensional In^{1+} chains in InTe. We demonstrate that InTe exhibits a bandgap of about 0.40±0.02 eV located at the M point of the Brillouin zone. Additionally, line defects are observed in our sample and were attributed to In^{1+} chain vacancy along the c-axis—a general feature in many other TlSe-like compounds. Our STS and DFT results prove that the presence of In^{1+} induces a localized gap state, located near the valence band maximum. This acceptor state is responsible for the high intrinsic p-type doping of InTe that we also confirm using angle-resolved photoemission spectroscopy.