Segregation of impurities in GaAs and InAs nanowires

TL;DR

This study uses ab initio density functional theory to analyze impurity segregation and formation energies in GaAs and InAs nanowires, revealing how impurity distribution depends on crystal structure and growth conditions.

Contribution

It provides new insights into impurity behavior in nanowires, highlighting the influence of crystal structure and surface effects on impurity placement.

Findings

Gold and oxygen prefer surface locations, consistent with experiments.

Silicon's preferred site varies with crystal structure, affecting doping.

Beryllium tends to diffuse into the nanowire center, explaining experimental observations.

Abstract

Using ab initio methods based on the density functional theory, we investigate the segregation and formation energies for various dopants (Si, Be, Zn, Sn), commonly used to obtain p- or ntype conductivity in GaAs and InAs nanowires. The distribution of Au and O atoms, which may be unintentionally incorporated during the wire growth, is also studied. The calculations performed for nanowires of zinc blende and wurtzite structure show that the distribution of most of the impurities depends on the crystal structure of the wires. For example, it is shown that the same growth conditions can lead to lower energy for Si substituting Ga (donor) in the wire of wurtzite structure and substituting As (acceptor) in the wire of zinc blende structure. In contrast, we obtain that gold and oxygen atoms always tend to stay at the lateral surfaces of GaAs and InAs nanowires, in agreement with experimental findings, while for beryllium the lowest energies are found when the impurities are located in sites in the center of the wurtzite wire or along the [1; 0; 1] axis from surface to the center of the zinc blende wire, what can explain the recently observed diffusion of this impurity into the volume of GaAs wires.