The structure, formation energy, binding energy and transfer levels of the Zn-P vacancy complex, [ZnIn-VP], in Zn-doped p-type material were studied as a function of the charge by using plane-wave ab initio density functional theory local density approximation calculations in a 64-atom super-cell. A binding energy of 0.39eV was found for the complex, which was neutral in p-type material; the 0/–1 transfer level lying 0.50eV above the valence-band edge. This was all in agreement with positron annihilation data. The results indicated that, whereas the formation of P vacancies, (VP+1), might be involved in carrier compensation in heavily Zn-doped material, the formation of Zn-vacancy complexes was not. For charge states, Q = +6 →-4, the Zn atom was in an sp2-bonded DX position and electrons, added or removed, went to or came from the remaining dangling bonds on the triangle of In atoms. This reduced the effective vacancy volume monotonically as electrons were added to the complex. The reduction occurred via a combination of increased In-In bonding and increased Zn-In electrostatic attraction. For certain charge states, a complex Jahn-Teller behavior was found in which up to 3 different structures (with the In triangle dimerized, anti-dimerized or symmetrical) were stable and close to degenerate. It was possible to predict and explain the structural behavior of this complex by using a simple tight-binding model.

Structure of the [ZnIn-VP] Defect Complex in Zn-Doped InP. C.W.M.Castleton, S.Mirbt: Physical Review B, 2003, 68[8], 085203