We use a science-grade Skipper Charge Coupled Device (Skipper-CCD) operating
in a low-radiation background environment to develop a semi-empirical model
that characterizes the origin of single-electron events in CCDs. We identify,
separate, and quantify three independent contributions to the single-electron
events, which were previously bundled together and classified as “dark
counts”: dark current, amplifier light, and spurious charge. We measure a dark
current, which depends on exposure, of (5.89+-0.77)x10^-4 e-/pix/day, and an
unprecedentedly low spurious charge contribution of (1.52+-0.07)x10^-4 e-/pix,
which is exposure-independent. In addition, we provide a technique to study
events produced by light emitted from the amplifier, which allows the
detector’s operation to be optimized to minimize this effect to a level below
the dark-current contribution. Our accurate characterization of the
single-electron events allows one to greatly extend the sensitivity of
experiments searching for dark matter or coherent neutrino scattering.
Moreover, an accurate understanding of the origin of single-electron events is
critical to further progress in ongoing R&D efforts of Skipper and conventional
CCDs.
Read More