Abstract
We employed density functional theory to investigate the structural, electronic, and optical properties of α-Te tubular nanostructures. These α-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 α-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 α-Te nanotubes but also opening up new possibilities for use in device applications.
Highlights
Tellurium (Te) is an important p-type semiconductor with a narrow bandgap of ∼0.35 eV.12 It exhibits good photoconductivity, thermoelectric effect, catalytic activity, high piezoelectricity13–16 and has been used in piezoelectric devices,17 gas sensors,18 topological insulators,19 and other various optoelectronic devices
For the hexagonal crystal structure of tellurium, Te atoms are arranged in spiral chains with neighboring atoms rotated by 120○
We found that the indirect-todirect bandgap transition occurred in armchair NTs as the tube diameter is decreased to the case of (5, 5) NTs
Summary
Tellurium (Te) is an important p-type semiconductor with a narrow bandgap of ∼0.35 eV.12 It exhibits good photoconductivity, thermoelectric effect, catalytic activity, high piezoelectricity13–16 and has been used in piezoelectric devices,17 gas sensors,18 topological insulators,19 and other various optoelectronic devices.20. First-principles simulations were performed to explore structural, electronic, and optical properties of armchair and zigzag α-Te NTs. We found that the indirect-todirect bandgap transition occurred in armchair NTs as the tube diameter is decreased to the case of (5, 5) NTs. The electronic properties of α-Te NTs are further investigated by the density of state and charge densities.
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