Homoepitaxial growth of CaWO₄

Rare earth ion (REI)-doped dielectric crystals are a promising materials platform for quantum device applications due to their stable and highly coherent optical transitions. Recently REIs in thin film hosts have become attractive because of their enhanced control of stoichiometry, lattice structure, and dimensionality. For thin films, the surface and interface structure at the atomic scale are important determinants of the optical properties by the presence of defects that can compromise the coherence time of quantum devices. In this talk, we describe the impact of thermal annealing on the surface morphology of a promising host crystal, CaWO₄. Our findings reveal that crystal miscut plays a significant role in determining the surface step-terrace structure at the atomic level. Additionally, by iterating an anneal-wet etch cycle, we can produce atomically flat surfaces with a roughness of less than 0.5Å rms over a 1um × 1um area. Homoepitaxial thin film growth using molecular beam epitaxy on an atomically flat surface of CaWO₄ results in high quality thin films. Our study establishes processing conditions necessary to realize high performance quantum optical systems based on REIs in CaWO₄ thin films.