Scandium nitride (ScN) is an emerging rock salt indirect bandgap semiconductor and has attracted significant interest in recent years for thermoelectric energy conversion, as a substrate for defect-free GaN growth, as a semiconducting component in single-crystalline metal/semiconductor superlattices for thermionic energy conversion, as well as for Al1−xScxN-based bulk and surface acoustic devices for 5G technologies. Most ScN film growth traditionally utilizes physical vapor deposition techniques such as magnetron sputtering and molecular beam epitaxy, which results in stoichiometric films but with varying crystal quality, orientations, microstructures, and physical properties. As epitaxial single-crystalline ScN films with smooth surfaces are essential for device applications, it is important to understand the ScN growth modes and parameters that impact and control their microstructure. In this Letter, we demonstrate that large adatom mobility is essential to overcome the Ehrlich–Schwoebel (E–S) and grain boundary migration barriers and achieve defect (voids, dislocations, stacking faults, etc.)-free single-crystalline ScN films. Using the substrate temperature to tune adatom mobility, we show that nominally single-crystalline ScN films are achieved when the homologous temperature is higher than ∼0.3. For homologous temperatures ranging from 0.23 to 0.30, ScN films are found to exhibit significant structural voids in between pyramidal growth regions with multiple in-plane orientations resulting from additional lateral growth off the facets of the pyramids and broken epitaxy after ∼80 nm of growth. The in-depth discussion of the growth modes of ScN presented here explains its varying electrical and optical properties and will help achieve high-quality ScN for device applications.

中文翻译：

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吸附原子迁移率和 Ehrlich-Schwoebel 势垒对氮化钪 (ScN) 薄膜异质外延生长的影响

氮化钪 (ScN) 是一种新兴的岩盐间接带隙半导体，近年来在热电能量转换、作为无缺陷 GaN 生长的衬底、作为热离子的单晶金属/半导体超晶格中的半导体组件方面引起了极大的兴趣。能量转换，以及用于 5G 技术的基于 Al1−xScxN 的体和表面声学设备。大多数 ScN 薄膜生长传统上使用物理气相沉积技术，如磁控溅射和分子束外延，这会产生化学计量薄膜，但具有不同的晶体质量、取向、微观结构和物理特性。由于具有光滑表面的外延单晶 ScN 薄膜对于器件应用至关重要，了解影响和控制其微观结构的 ScN 生长模式和参数非常重要。在这封信中，我们证明了大吸附原子迁移率对于克服 Ehrlich-Schwoebel (E-S) 和晶界迁移障碍并实现无缺陷（空隙、位错、堆垛层错等）的单晶 ScN 薄膜至关重要。使用衬底温度来调整吸附原子迁移率，我们表明当同源温度高于~0.3 时，可以获得名义上的单晶 ScN 薄膜。对于范围从 0.23 到 0.30 的同源温度，发现 ScN 薄膜在锥体生长区域之间表现出显着的结构空隙，具有多个面内取向，这是由于在约 80 nm 的生长后从锥体的小平面上额外横向生长和破裂的外延造成的。