Electronic band gap of van der Waals alpha-As2Te3 crystals

van der Waals materials offer a large variety of electronic properties depending on chemical composition, number of layers, and stacking order. Among them, As2Te3 has attracted attention due to the promise of outstanding electronic properties and high photo-response. Precise experimental determinations of the electronic properties of As2Te3 are yet sorely needed for better understanding of potential properties and device applications. Here, we study the structural and electronic properties of alpha-As2Te3. Scanning transmission electron microscopy coupled to energy x-ray dispersion and micro-Raman spectroscopy all confirm that our specimens correspond to alpha-As2Te3. Scanning tunneling spectroscopy (STS) at 4.2 K demonstrates that alpha-As2Te3 exhibits an electronic bandgap of about 0.4 eV. The valence-band maxima are located at -0.03 eV below the Fermi level, thus confirming the residual p-type character of our samples. The material can be exfoliated, revealing the (100) anisotropic surface. Transport measurements on a thick exfoliated sample (bulk-like) confirm the STS results. These findings allow for a deeper understanding of the As2Te3 electronic properties, underlying the potential of V-VI semiconductors for electronic and photonic technologies.