Observation of electron-hole pair quantization in a high voltage cryogenic silicon detector with superconducting phonon sensor readout

We demonstrate that individual electron-hole pairs are resolved in a 1cm$^2$ by 4mm thick silicon crystal (0.93g) operated at $\sim$35mK. One side of the detector is patterned with two quasiparticle-trap-assisted electro-thermal-feedback transition edge sensor (QET) arrays held near ground potential. The other side contains a bias grid with 20% coverage. Bias potentials up to $\pm$160V were used in the work reported here. A fiber optic provides 650nm (1.9eV) photons that each produce an electron-hole ($e^{-} h^{+}$) pair in the crystal near the grid. The energy of the drifting charges is measured with a phonon sensor noise $\sigma$ $\sim$0.09 $e^{-} h^{+}$ pair. The observed charge quantization is nearly identical for $h^+$'s or $e^-$'s transported across the crystal.