The lattice locations of Zn atoms in heavily Zn-doped InP single cryst
al have been investigated by ion channeling techniques. The InP sample
s were rapidly quenched in diffusion pump oil after high-temperature Z
n diffusion. Ion channeling experiments performed along various major
crystal axes suggest that a large fraction (20%-30%) of the Zn atoms a
re in the tetrahedral interstitial position in the InP lattice. It has
been found that although the maximum hole concentration is not signif
icantly affected by the cooling rate, there is a substantial increase
in the incorporation of Zn on substitutional and tetrahedral interstit
ial lattice locations in the rapidly cooled samples as compared to the
slowly cooled samples. The consequences of these results for understa
nding the mechanisms leading to the saturation of the free-hole concen
tration in compound semiconductors are discussed.