Mutual passivation of electrically active and isovalent impurities

Mutual passivation of electrically active and isovalent impurities in dilute nitrides

Using first-principles calculations we investigate the mutual passivation of shallow donor Si and isovalent N in dilute GaAsN alloys. Instead of the recently proposed pairing of Si and N on adjacent substitutional sites (Si(Ga)-N(As)) [K. M. Yu et al., Nat. Mater. 1, 185 (2002); J. Li et al., Phys. Rev. Lett. 96, 035505 (2006)] we find that N changes the behavior of Si in dilute nitride alloys in a more dramatic way. N and Si combine into a deep-acceptor split interstitial, where Si and N share an As site [(Si-N) (As)], with a significantly lower formation energy than that of the Si(Ga)-N(As) pair in n-type GaAs and dilute GaAsN alloys. The formation of (Si-N)(As) explains the GaAs band-gap recovery and the appearance of a photoluminescence peak at approximately 0.8 eV. This model can also be extended to Ge-doped GaAsN alloys, and correctly predicts the absence of mutual passivation in the case of column-VI dopants.

Mutual passivation of donors and isovalent nitrogen in GaAs

We study the mutual passivation of shallow donor and isovalent N in GaAs. We find that all the donor impurities, SiGa, GeGa, SAs, and SeAs, bind to N in GaAs:N, which has a large N-induced band-gap reduction relative to GaAs. For a group-IV impurity such as Si, the formation of the nearest-neighbor SiGa-NAs defect complex creates a deep donor level below the conduction band minimum (CBM). The coupling between this defect level with the CBM pushes the CBM upwards, thus restoring the GaAs band gap; the lowering of the defect level relative to the isolated SiGa shallow donor level is responsible for the increased electrical resistivity. Therefore, Si and N mutually passivate each other's electrical and optical activities in GaAs. For a group-VI shallow donor such as S, the binding between SAs and NAsdoes not form a direct bond; therefore, no mutual passivation exists in the GaAs:(S+N) system.