Ionization yield in silicon for eV-scale electron-recoil processes

Abstract

The development of single charge resolving, macroscopic silicon detectors has opened a window into rare processes at the O(eV) scale. In order to reconstruct the energy of a given event, or model the charge signal obtained for a given amount of energy absorbed by the electrons in a detector, an accurate charge yield model is needed. In this paper we review existing measurements of charge yield in silicon, focusing in particular on the region below 1 keV. We highlight a calibration gap between 12-50 eV (referred to as the "UV-gap") and employ a phenomenological model of impact ionization to explore the likely charge yield in this energy regime. Finally, we explore the impact of variations in this model on a test case, that of dark matter scattering off electrons, to illustrate the scientific impact of uncertainties in charge yield.

Constraints on the electron-hole pair creation energy and Fano factor below 150 eV from Compton scattering in a Skipper-CCD

“…This result is similar to the one previously obtained using Skipper-CCDs at 5.9 keV and 123 K [22], where a pair creation energy of (3.749 ± 0.001) eV was reported. Even though these values depend on the interaction energy and lattice temperature and cannot be compared directly, they seem within the expectation of extrapolating to lower energy and are also consistent with other measurements performed using silicon-based technologies and semi-empirical models [23,31,32].…”

“…Our results are consistent with previous work using the same technology but measured at higher energy and different operating temperature. Theoretical expectations and other measurements with silicon-based technologies are also consistent with our re-sults [23,31,32]. Finally, the size of the step corresponding to the second and third L-shells (99.3 eV) is not consistent with the simple theoretical expectation that only considers the change in the number of available electronic targets on which photons may scatter.…”

“…Characterizing the Compton spectrum, electron-hole pair creation energy, and Fano factor is one of the main challenges in understanding the background for measurements at energies below 100 eV, and modeling interactions between new particles and silicon electrons or nuclei [23]. Below, we present a first measurement of the Compton spectrum using a Skipper-CCD operated with sub-electron resolution and irradiated with a 241 Am radioactive source.…”

Design and characterization of a phonon-mediated cryogenic particle detector with an eV-scale threshold and 100 keV-scale dynamic range

“…where e is the elementary charge, n eh is the number of electron-hole pairs produced, V NTL is the bias applied across the detector and ε γ ðE r Þ is the average energy required to produce an electron-hole pair. While ε γ can be approximated by a constant 3.8 eV in silicon for high energy interactions, ε γ ðE r Þ is a function of the initial energy in the case of a few charge carriers [27,28]. The signal can be amplified to the point that the detector is sensitive to a single electron-hole pair.…”

Cryogenic Detector Development for SuperCDMS

“…It should be noted that present measurements of ε γ and F are generally for higher energies and material temperatures than the SuperCDMS detectors operate. However, there are current efforts to leverage current theory to extend our understanding to lower energies and temperatures [133]. Models and previous measurements of the yield in Si and Ge are shown in Fig.…”