  We present the results of a large-scale survey of neutron(n)-capture elements
in Galactic planetary nebulae (PNe), undertaken to study enrichments from
s-process nucleosynthesis in their progenitor stars. From new K band
observations of over 100 PNe supplemented by data from the literature, we have
detected the emission lines [Kr III] 2.199 and/or [Se IV] 2.287 $\mu$m in 81 of
120 objects. We determine Se and Kr elemental abundances, employing ionization
correction formulae derived in the first paper of this series. We find a
significant range in Se and Kr abundances, from near solar (no enrichment) to
enhanced by >1.0 dex relative to solar, which we interpret as self-enrichment
due to in situ s-process nucleosynthesis. Kr tends to be more strongly enriched
than Se; in 18 objects exhibiting both Se and Kr emission, we find that [Kr/Se]
= 0.5$\pm$0.2.
  Our survey has increased the number of PNe with n-capture element abundance
determinations by a factor of ten, enabling us for the first time to search for
correlations with other nebular properties. As expected, we find a positive
correlation between s-process enrichments and the C/O ratio. Type I and bipolar
PNe, which arise from intermediate-mass progenitors (>3-4 solar masses),
exhibit little to no s-process enrichments. Finally, PNe with H-deficient
Wolf-Rayet central stars do not exhibit systematically larger s-process
enrichments than objects with H-rich nuclei. Overall, 44% of the PNe in our
sample display significant s-process enrichments (>0.3 dex). Using an empirical
PN luminosity function to correct for incompleteness, we estimate that the true
fraction of s-process enriched Galactic PNe is at least 20%.
