First-principles electronic structure study of InxGa1−xAs nanotubes and InAs/GaAs nanotube superlattices

The first-principles all-electron calculations with numerical atomic orbit basis set have been implemented to study the structural and electronic properties of single-wall (n, 0) InxGa1−xAs nanotubes and InAs/GaAs nanotube superlattices. The electronic bandstructure, projected density of states, total electronic density and electron electrostatic potential are investigated, and the band-gap variations with parameter n and alloy concentration x are analyzed. The valence band and high energy conduction band states dominantly come from the contributions of p atomic orbits, while the lower conduction band states originate primarily from p (x < 0.30) or s (x > 0.70) atomic orbits for the InxGa1−xAs nanotubes. The InxGa1−xAs nanotubes exhibit 0.96-3.54 μm near-infrared direct band-gaps of semiconductor band structure, decreasing with increased In alloy concentration and diminished nanotube diameter (proportional to n), with negative band-gap bowing coefficients of −0.15-−0.31 eV reducing with increased n. The equal and opposite in direction dipoles are produced by III-group atoms at the consecutive InAs and GaAs interfaces in InAs/GaAs nanotube superlattices. The InAs/GaAs nanotube superlattices show direct band-gap semiconductor band structures, and the band-gap explicitly varies with the superlattice period and nanotube diameter, corresponding 2.21-6.20 μm infrared region. The results indicate the possibility of flexible band-engineering the band-gaps of InAs/GaAs nanotube superlattices for optoelectronic applications by adjusting nanotube segment length and nanotube diameter.