Doping effects of C, Si and Ge in wurtzite [0001] GaN, AlN, and InN nanowires

We have performed an ab initio investigation, within the spin-polarized density functional theory, of the energetic stability and electronic properties of substitutional Si, Ge, and C impurities in [0001] GaN, AlN, and InN nanowires (NWs). Our total energy results show that C impurities in the cation site (C-Ga, C-Al, and C-In) present lower formation energies at the surface of the NWs as compared to their counterparts in the core of the NW or the bulk system. In these position donor likely properties are obtained for GaN and InN NWs, whereas for the AlN NW deep levels are observed inside the bandgap. In contrast, C-N must be distributed uniformly along the NW diameter and gives rise to a deep electronic level inside the NW bandgap. Si in GaN and InN and Ge in InN are most stable at the cation site in the core of the NWs, and lead the systems to show a n-type semiconductor properties. For the AlN NW we obtain that Si and Ge are most likely in a N site at the surface of the NW and introduce deep levels inside the NW bandgap. Meanwhile, C and Ge impurities are amphoteric impurities in GaN NWs. (C) 2011 American Institute of Physics. [doi:10.1063/1.3607280]