Diffusion and Defects in Elementary and Compound Semiconductors
Mechanism of zinc diffusion in gallium arsenide
We have performed zinc diffusion experiments in gallium arsenide at temperatures between 620oC
and 870oC with a dilute Ga-Zn source. The low Zn partial pressure established during
annealing realizes Zn surface concentrations ≤ 2x1019 cm-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.
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