Effect of N interstitial complexes on the electronic properties of GaAs 1 − x N x alloys from first principles

VENTURA, CECILIA I.; FUHR, JAVIER D.; QUERALES-FLORES, JOSÉ D.

Physical Review Materials

APS

Año: 2019 vol. 3

Although several approaches have been used in the past to  investigate the impact of nitrogen (N) on the electronic structure  of GaAs$_{1-x}$N$_{x}$ alloys, there is no agreement between theory  and experiments about the importance of the different N interstitial  defects in these alloys, and their nature is still unknown.  Here we  analyze the impact of five different N defects on the electronic  structure of GaAs$_{1-x}$N$_{x}$ alloys, using density-functional  methods: we calculate electronic states, formation energies and  charge transition levels. The studied defects include  N$_extrm{As}$, As$_extrm{Ga}$, As$_extrm{Ga}$-N$_extrm{As}$  substitutional defects, and (N-N)$_extrm{As}$,  (N-As)$_extrm{As}$ split-interstitial complex defects. Our  calculated defect formation energies agree with those reported by  S.B. Zhang et al. [Phys. Rev. Lett. 86, 1789 (2001)], who predicted  these defects.  Among the interstitial defects, we found that  (N-As)$_extrm{As}$ emerges as the lowest energy configuration in  comparison with (N-N)$_extrm{As}$, in agreement with recent  experiments [T. Jen, et al., Appl. Phys. Lett. 107, 221904 (2015)].  We also calculated the levels induced in the electronic structure  due to each of these defects: defect states may occur as deep levels  in the gap, shallow levels close to the band edges, and as levels  resonant with bulk states.  We find that the largest changes in the  band structure are produced by an isolated N atom in GaAs, which is  resonant with the conduction band, exhibiting a strong hybridization  between N and GaAs states. Deeper levels in the bandgap are obtained  with (N-N)$_extrm{As}$ split-interstitial defects. Our results  confirm the formation of highly localized states around the N sites,  which is convenient for extcolor{red}{photovoltaics and photoluminescence} applications.