  We present direct imaging measurements of charge transport across a 1 cm x 1
cm x 4 mm-thick crystal of high purity silicon ($\sim$15 k$\Omega$-cm) at
temperatures of 5 K and 500 mK. We use these data to measure the lateral
diffusion of electrons and holes as a function of the electric field applied
along the [111] crystal axis, and to verify our low-temperature Monte Carlo
software. The range of field strengths in this paper exceed those used in the
previous study (DOI: 10.1063/1.5049691) by a factor of 10, and now encompasses
the region in which some recent silicon dark matter detectors operate (DOI:
10.1103/PhysRevLett.121.051301). We also report on a phenomenon of surface
charge trapping which can reduce expected charge collection.
