Spatial Imaging of Charge Transport in Silicon at Low Temperature

We present direct imaging measurements of charge transport across a 1 cm by 1 cm by 4 mm crystal of high purity silicon (20 kOhm*cm) at temperatures between 500 mK and 5 K. We use these data to determine the intervalley scattering rate of electrons as a function of the electric field applied along the [111] crystal axis, and we present a phenomenological model of intervalley scattering that explains the constant scattering rate seen at low-voltage for cryogenic temperatures. We also present a measurement of the collection efficiency for drifting electrons and holes in Si as a function of temperature from 300 K down to 1 K, from which we have gained insight into low-temperature phonon physics, charge trapping, and impact ionization.