Toward Single Electron Resolution Phonon Mediated Ionization Detectors

TL;DR

This paper presents advancements in phonon-mediated ionization detectors with single electron resolution, achieved through improved contact interface design, higher bias voltages, and phonon gain, enhancing sensitivity for rare event detection.

Contribution

The paper introduces a new detector design with vacuum-separated electrodes enabling higher bias voltages and phonon gain, significantly improving resolution over previous models.

Findings

Achieved RMS resolution of ~7 eV$_{ee}$ with increased bias voltage and phonon gain.

Proposed interface materials and thicker substrates could reach resolutions of ~2.8 eV$_{ee}$.

Investigating insulator layers may enable resolution of ~1 eV.

Abstract

Experiments seeking to detect rare event interactions such as dark matter or coherent elastic neutrino nucleus scattering are striving for large mass detectors with very low detection threshold. Using Neganov-Luke phonon amplification effect, the Cryogenic Dark Matter Search (CDMS) experiment is reaching unprecedented RMS resolutions of ~ 14 eV$_{ee}$ . CDMSlite is currently the most sensitive experiment to WIMPs of mass $\sim$5 GeV/c$^{2}$ but is limited in achieving higher phonon gains due to an early onset of leakage current into Ge crystals. The contact interface geometry is particularly weak for blocking hole injection from the metal, and thus a new design is demonstrated that allows high voltage bias via vacuum separated electrode. With an increased bias voltage and a $\times$ 2 Luke phonon gain, world best RMS resolution of sigma $\sim$7 eV$_{ee}$ for 0.25 kg (d=75 mm, h=1 cm) Ge detectors was achieved. Since the leakage current is a function of the field and the phonon gain is a function of the applied voltage, appropriately robust interface blocking material combined with thicker substrate (25 mm) will reach a resolution of $\sim$2.8 eV$_{ee}$. In order to achieve better resolution of $\sim$ eV, we are investigating a layer of insulator between the phonon readout surface and the semiconductor crystals.