Dead layer on silicon p–i–n diode charged-particle detectors

Abstract

Semiconductor detectors in general have a dead layer at their surfaces that is either a result of natural or induced passivation, or is formed during the process of making a contact. Charged particles passing through this region produce ionization that is incompletely collected and recorded, which leads to departures from the ideal in both energy deposition and resolution. The silicon p-i-n diode used in the KATRIN neutrinomass experiment has such a dead layer. We have constructed a detailed Monte Carlo model for the passage of electrons from vacuum into a silicon detector, and compared the measured energy spectra to the predicted ones for a range of energies from 12 to 20 keV. The comparison provides experimental evidence that a substantial fraction of the ionization produced in the "dead" layer evidently escapes by diffusion, with 46% being collected in the depletion zone and the balance being neutralized at the contact or by bulk recombination. The most elementary model of a thinner dead layer from which no charge is collected is strongly disfavored.

Focal-plane detector system for the KATRIN experiment

“…A comparison of simulated spectra to photoelectron data taken in Seattle revealed this assumption to be inaccurate: some charge deposited in the dead layer is collected as part of the measured pulse. With this more realistic definition, the dead-layer thickness was found to be 155.4 ± 0.5 stat ± 0.2 sys nm with 46% charge collection [25]. The precision of this measurement, and of the simulation package developed for electron interaction in our detector [26], allows our analysis tools to compensate for the deviation from the original specification.…”

First operation of the KATRIN experiment with tritium

“…The large main spectrometer acts as a MAC-E filter, transmitting only electrons with a kinetic energy E above the retarding energy qU (where q is the elementary charge and U is the retarding voltage of the spectrometer). At the end of the beamline a segmented Si-detector with 148 pixels (focal plane detector, FPD [12,13]) counts the number of transmitted electrons as a function of retarding voltages of the main spectrometer. The shape of the integral β-electron spectrum is obtained by counting at a pre-defined set of different retarding voltages.…”

Kassiopeia: a modern, extensible C++ particle tracking package

“…• 'Investigation of the passage of electrons from vacuum into the active volume of a p-i-n diode charged particle detector' [70]: electron tracking and diffusion in silicon.…”