Rare-earth ion-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 form have become attractive because of their enhanced control of stoichiometry, lattice structure, and dimensionality. This flexibility provides a versatile host crystal environment. Control of surface and interface structures of host crystals at the atomic scale offers an avenue to further improve the optical properties of the system by mitigating defects, which can otherwise compromise the coherence time of quantum devices. In this work, we have investigated 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 annealing-wet etch cycle, we have achieved atomically flat surfaces with a roughness of less than 0.5 Å rms over a 1 × 1 μm2 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 guiding principles to realize a novel quantum optical system based on REI-doped CaWO4 thin films.

中文翻译：

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CaWO4同质外延生长

稀土离子掺杂介电晶体由于其稳定且高度相干的光学跃迁而成为量子器件应用的有前途的材料平台。最近，薄膜形式的 REI 因其对化学计量、晶格结构和维度的增强控制而变得有吸引力。这种灵活性提供了一个多功能的主机晶体环境。在原子尺度上控制主晶体的表面和界面结构，为通过减少缺陷来进一步改善系统的光学特性提供了途径，否则缺陷可能会影响量子器件的相干时间。在这项工作中，我们研究了热退火对一种有前途的基质晶体 CaWO4 表面形态的影响。我们的研究结果表明，晶体误切在原子水平上确定表面台阶结构方面起着重要作用。此外，通过迭代退火-湿法蚀刻循环，我们在 1 × 1 μm2 区域上实现了粗糙度小于 0.5 Å rms 的原子级平坦表面。使用分子束外延在 CaWO4 的原子级平坦表面上进行同质外延薄膜生长，可产生高质量的薄膜。我们的研究确立了实现基于 REI 掺杂 CaWO4 薄膜的新型量子光学系统的指导原则。