N-doped ZnO nanowires: Surface segregation, the effect of hydrogen passivation and applications in spintronics

We employ density-functional theory (DFT) within the generalized-gradient approximation (GGA) to investigate the formation energies, electronic structure, and magnetic properties of N impurities in zinc oxide (ZnO) nanowires. While the subsurface position is the preferential site for the N dopants in bare nanowires, upon hydrogen passivation N atoms segregate to surface sites. Additionally we show that the defect levels in these ultra-thin wires are deeper than the ones in bulk ZnO, suggesting strong quantum dimensional effects. Finally we investigate the possibility of ferromagnetism induced by N in ZnO nanowires. Our spin-polarized calculations show that, although N introduces a small net magnetic moment in ZnO, the interaction between N dopants is weak and strongly dependent on the N position.