Low microwave loss in deposited Si and Ge thin-film dielectrics at single-photon power and low temperatures

Our study shows that deposited Ge and Si dielectric thin-films can exhibit low microwave losses at near single-photon powers sub-Kelvin temperatures ($\approx$40 mK). This loss enables their use in a wide range of devices, including low-loss coplanar, microstrip, stripline resonators, as well layers for device isolation, inter-wiring dielectrics, passivation Josephson junction circuit fabrication. We coplanar resonator structures with narrow trace widths 2-16 $\mu \textrm{m}$ to maximize the sensitivity tangent measurements interface properties rather than optimize quality factor. In this configuration, thermally-evaporated $\approx 1 \mu thick amorphous germanium (a-Ge) films on (100) have single photon $1-2\times10^{-6}$ and, $9 \textrm{m}$-thick chemical vapor (CVD) homoepitaxial has $0.6-2\times 10^{-5}$. Interface contamination limits these devices.