Zinc diffusion in gallium arsenide and the properties of gallium interstitials

Abstract

We have performed zinc diffusion experiments in gallium arsenide at temperatures between $620\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and $870\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ with a dilute $\mathrm{Ga}\ensuremath{-}\mathrm{Zn}$ source. The low Zn partial pressure established during annealing realizes Zn surface concentrations of $\ensuremath{\leqslant}2\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, which lead to the formation of characteristic S-shaped diffusion profiles. Accurate modeling of the Zn profiles, which were measured by means of secondary ion mass spectroscopy, shows that Zn diffusion under the particular doping conditions is mainly mediated by neutral and singly positively charged Ga interstitials via the kick-out mechanism. We determined the temperature dependence of the individual contributions of neutral and positively charged Ga interstitials to Ga diffusion for electronically intrinsic conditions. The data are lower than the total Ga self-diffusion coefficient and hence consistent with the general interpretation that Ga diffusion under intrinsic conditions is mainly mediated by Ga vacancies. Our results disprove the general accepted interpretation of Zn diffusion in GaAs via doubly and triply positively charged Ga interstitials and solves the inconsistency related to the electrical compensation of the acceptor dopant Zn by the multiply charged Ga interstitials.