Measuring the impact ionization and charge trapping probabilities in SuperCDMS HVeV phonon sensing detectors

A 0.93 g 1 x 1 x 0.4 cm(3) SuperCDMS silicon HVeV detector operated at 30 mK was illuminated by 1.91 eV photons using a room temperature pulsed laser coupled to the cryostat via fiber optic. The detector's response under a variety of specific operating conditions was used to study the detector leakage current, charge trapping, and impact ionization in the high-purity Si substrate. The measured probabilities for a charge carrier in the detector to undergo charge trapping (0.713 +/- 0.093%) or cause impact ionization (1.576 +/- 0.110%) were found to be nearly independent of bias polarity and charge-carrier type (electron or hole) for substrate biases of +/- 140 V.