Structure and electronic properties of GaN nanotubes (GaNNTs) are investigated by using ab initio density functional theory. By full optimization, the optimized structures (bondlengths and angles between them) of zigzag GaNNTs (n, 0) and armchair GaNNTs (a, n) (4 < n < 11) are calculated. The difference between nitrogen ring diameter and gallium ring diameter (buckling distance) and semiconducting energy gap in term of diameter for zigzag and armchair GaNNTs have also been calculated. We found that buckling distance decreases by increasing nanotube diameter. Furthermore, we have investigated the effects of nitrogen and gallium vacancies on structure and electronic properties of zigzag GaNNT (5, 0) using spin dependent density functional theory. By calculating the formation energy, we found that N vacancy in GaNNT (5, 0) is more favorable than Ga vacancy. The nitrogen vacancy in zigzag GaNNT induces a 1.0 mu(B) magnetization and makes a polarized Structure. We have shown that in polarized GaNNT a flat band near the Fermi energy splits to occupied spin tip and unoccupied spin down levels
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