  Understanding and characterizing very low-energy ($\sim$eV) background
sources is a must in rare-event searches. Oscura, an experiment aiming to probe
electron recoils from sub-GeV dark matter using a 10-kg skipper-CCD detector,
has recently fabricated its first two batches of sensors. In this work, we
present the characterization of defects/contaminants identified in the
buried-channel region of these newly fabricated skipper-CCDs. These
defects/contaminants produce deferred charge from trap emission in the images
next to particle tracks, which can be spatially resolved due to the
sub-electron resolution achieved with these sensors. Using the trap-pumping
technique, we measured the energy and cross section associated to these traps
in three Oscura prototype sensors from different fabrication batches which
underwent different gettering methods during fabrication. Results suggest that
the type of defects/contaminants is more closely linked to the fabrication
batch rather than to the gettering method used. The exposure-dependent
single-electron rate (SER) of one of these sensors was measured $\sim$100~m
underground, yielding $(1.8\pm 0.3)\times10^{-3}~e^-$/pix/day at 131K. The
impact of the identified traps on the measured exposure-dependent SER is
evaluated via a Monte Carlo simulation. Results suggest that the
exposure-dependent SER of Oscura prototype sensors would be lower in lower
background environments as expected.
