Structure of the [ZnIn-VP] defect complex in Zn-doped InP -: art. no. 085203

We study the structure, formation energy, binding energy and transfer levels of the zinc-phosphorus vacancy complex [Zn-In-V-P] in Zn-doped p-type InP, as a function of the charge, using plane-wave ab initio density functional theory local density approximation calculations in a 64-atom supercell. We find a binding energy of 0.39 eV for the complex, which is neutral in p-type material, the 0/-1 transfer level lying 0.50 eV above the valence-band edge, all in agreement with recent positron annihilation experiments. Our results indicate that, while the formation of phosphorus vacancies (V-P(+1)) may be involved in carrier compensation in heavily Zn-doped material, the formation of Zn-vacancy complexes is not. Regarding the structure, for charge states Q=+6-->-4 the Zn atom is in an sp(2)-bonded DX position and electrons added (removed) go to (come from) the remaining dangling bonds on the triangle of In atoms. This reduces the effective vacancy volume monotonically as electrons are added to the complex, resolving a recent debate between contradicting experiments. The reduction occurs through a combination of increased In-In bonding and increased Zn-In electrostatic attraction. In addition, for certain charge states we find complex Jahn-Teller behavior in which up to three different structures (with the In triangle dimerized, antidimerized, or symmetric) are stable and close to degenerate. We are able to predict and successfully explain the structural behavior of this complex using a simple tight-binding model.