Effect of d-orbitals on the energy gap of group-III nitrides nanostructures

We have developed a tight-binding Hamiltonian model to study the band structure of group-III nitride nanostructures, AlN, GaN and InN in the form of monolayer sheets, nanotubes (NT) and nanoribbons (NR). We have considered the semi-empirical sp3d5s* tight-binding model taking into account the nearest neighbors. Based on our numerical results we obtained that d-orbitals are important for correct calculation of group-III nitride band structures. Also we have observed that the AlN, GaN and InN graphene-like sheets are semiconductors with indirect band gaps of 5.28 eV, 2.62 eV and 1.66 eV, respectively. We have seen that, our tight binding band gaps are larger than the corresponding band gaps obtained by DFT calculation. Also, we have investigated the effects of chirality of nanotubes and nanoribbons on the nitrides band structures and their gaps. Then, we have studied the influence of nanotube diameter and width of nanoribbon on the band structure. We observed that nanotubes and nanoribbons as the corresponding unzipped nanotubes have the same band structure. Moreover, we understand that the electronic properties are almost insensitive to diameter for nanotubes but width of nanoribbons is effective on the band structure.