High-field Spatial Imaging of Charge Transport in Silicon at Low Temperature

TL;DR

This study provides direct high-field imaging of charge transport in high-purity silicon at cryogenic temperatures, revealing diffusion behavior, verifying simulations, and identifying surface charge trapping effects relevant for dark matter detectors.

Contribution

It offers the first detailed imaging of charge transport at high fields and low temperatures in silicon, extending previous studies and including surface charge trapping phenomena.

Findings

Charge diffusion varies with electric field at low temperatures.

Verification of Monte Carlo simulations for charge transport.

Identification of surface charge trapping reducing charge collection.

Abstract

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.