Epitaxial deposition of highly enriched $^{28}$Si films with \textless 1 nm roughness

Low temperature epitaxial deposition of thin films with less than 1 nm rms roughness is achieved using a $^{28}$Si ion beam deposition source. These films are enriched \textit{in situ} to \textless 140 ppb $^{29}$Si isotope fraction for quantum computing devices. Removal of the 4.7 {\%} $^{29}$Si nuclear spins in natural silicon allows for exceedingly long coherence (T$_{2})$ times of qubits, making incorporation of highly enriched $^{28}$Si into devices critical for solid state quantum information. Low roughness epitaxial $^{28}$Si thin films are achieved by depositing in an island growth mode at temperatures of 300 \textdegree C to 400 \textdegree C, and the morphology is verified using scanning tunneling microscopy. Further, the crystalline quality of the films is shown using cross-sectional transmission electron microscopy. Finally, the chemical purity and broader electrical properties of the $^{28}$Si films are assessed by secondary ion mass spectroscopy as well as capacitance--voltage profiling, schottky diode measurements, and hall measurements.