Structural, electronic, and optical properties of α-Te tubular nanostructures: A first-principles study

We employed density functional theory to investigate the structural, electronic, and optical properties of alpha-Te tubular nanostructures. These alpha-Te tube-like structures, which are similar to carbon nanotubes in terms of their armchair and zigzag structures, are semiconductors with moderate bandgaps. The nanotubes in armchair configurations have an indirect-to-direct bandgap transition as tube diameter is decreased to a specific critical tube size, while those in zigzag configurations are always semiconductors with a direct gap independent of tube diameter. The calculated projected density of states reveals that such an indirect-to-direct bandgap transition found in armchair nanotubes can be attributed to the contributions of the different p-orbitals near the valence band maximum edges. The optical absorption spectra of alpha-Te nanotubes are found to be anisotropic and vary with the tube diameters. These findings are not only helpful for better understanding the physical characteristics of alpha-Te nanotubes but also opening up new possibilities for use in device applications. (C) 2019 Author(s).