The Structure of the [Zn_In - V_P] Defect Complex in Zn Doped InP

TL;DR

This study uses ab initio calculations to analyze the structure, energies, and electronic levels of the Zn-In - V_P defect complex in Zn-doped InP, revealing insights into its stability, charge states, and structural behavior.

Contribution

It provides detailed first-principles insights into the structure, energetics, and transfer levels of the Zn-In - V_P complex, including Jahn-Teller effects, which were not previously characterized.

Findings

Binding energy of 0.39 eV for the complex

Transfer level 0.50 eV above valence band edge

Structural variations due to Jahn-Teller effects

Abstract

We study the structure, the formation and binding energies and the 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 DFT-LDA 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. This indicates that, whilst the formation of phosphorus vacancies (V_P) 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 to -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 monatonically as electrons are added to the complex, also in agreement with experiment. 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 behaviour in which up to three different structures, (with the In triangle dimerised, antidimerised or symmetric) are stable and are close to degenerate. We are able to predict and successfully explain the structural behaviour of this complex using a simple tight binding model.