  We characterize single- and few-electron backgrounds that are observed in
dual-phase liquid xenon time projection chambers at timescales greatly
exceeding a maximum drift time after an interaction. These instrumental
backgrounds limit a detector's sensitivity to dark matter and cosmogenic
neutrinos. Using the ~150g liquid xenon detector at Purdue University, we
investigate how these backgrounds, produced after 122keV $^{57}$Co Compton
interactions, behave under different detector conditions. We find that the
rates of single- and few-electron signals follow power-laws with time after the
interaction. We observe linearly increasing rates with increased extraction
field, and increased rates in the single-electron background with increased
drift field. Normalizing the rates to the primary interaction's measured
ionization signal, the rates increase linearly with the depth of the
interaction. We test the hypothesis that infrared photons (1550nm) would
stimulate and accelerate electron emission via photodetachment from impurities,
but find that even 1 Watt of infrared light fails to reduce these backgrounds.
We thus provide a characterization that can inform background models for
low-energy rare event searches.
