First Principal Calculations on the Electronic Structure and the Optical Properties of Al-doped Zigzag GaN Nanotube

In this work, the electronic structures and the optical properties of Al-doped zigzag (10,0) GaN nanotubes are investigated using first-principles calculations. The examined structure of the GaN nanotube consists of 40 atoms (20 Ga and 20 N). The density functional theory (DFT) is carried out in the SIESTA package. The Gallium atoms were replaced by Al atoms according to the formula Ga1-xAlxN at various Al rates (x = 0, 0.2, 0.4, 0.6, 0.8, and 1). The electronic structure calculation showed that zigzag gallium nitride nanotube is a direct band gap semiconductor. When more aluminum atoms were substituted for gallium atoms, the energy gap increased from 1.72 to 2.74 eV. The projected density of the states (PDOS) exposed that the Ga-4p and Al-3p orbitals are the most dominant states in both valance and conduction bands. The optical properties, such as the real and imaginary parts of the dielectric constant, absorption coefficient, and reflectivity, are calculated. The optical results showed that substituting aluminum atoms shifts the absorption edge, supplying more wave spectrum. Moreover, adding more aluminum atoms reduced the energy loss and reflectivity inside the visible light range and improved the light sensitivity of the electronic structure.