Diffusion mechanism of Zn in InP and GaP from first principles

Abstract

The diffusion mechanism of Zn in GaP and InP has been investigated using first-principles computational methods. It is found that the kickout mechanism is the favored diffusion process under all doping conditions for InP, and under all except $n$-type conditions for GaP. In $n$-type GaP the dissociative mechanism is probable. In both $p$-type GaP and InP, the diffusing species is found to be ${\mathrm{Zn}}_{i}^{+2}$. The activation energy for the kickout process is $2.49\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ in GaP and $1.60\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ in InP, and therefore unintentional diffusion of Zn should be a larger concern in InP than in GaP. The dependence of the activation energy both on the doping conditions of the material and on the stoichiometry is explained, and found to be in qualitative agreement with the experimentally observed dependencies. The calculated activation energies agree reasonably with experimental data, assuming that the region from which Zn diffuses is $p$ type. Explanations are also found as to why Zn tends to accumulate at $pn$ junctions in InP and to why a relatively low fraction of Zn is found on substitutional sites in InP.