Abstract 'There is an interest in growing N-polar GaN on bulk GaN for high electron mobility transistors (HEMTs). Current N-polar HEMT technology is dominated by devices grown on non-native substrates which possess a high density of dislocations due to lattice mismatch. N-polar GaN films grown directly on non-miscut GaN substrates have displayed a high density of pits and depressions on the surface. This work demonstrates that surface impurities play a major role in the formation of surface-pits in epitaxially grown film. By subjecting the GaN substrate to an ultra-violet (UV) O3 (ozone) clean prior to growth and initiating growth with a 2 nm coherently strained AlN layer, grown under metal-rich conditions, we have demonstrated N-polar GaN films with a nearly pit-free surface. This AlN initiation layer (AIL) likely captures impurities on the substrate surface thus decoupling the substrate surface from the epitaxially grown film. It is demonstrated that utilizing thicker AILs, up to 8 nm, further improves film quality and surface morphology. The methods employed in this study to produce high-quality N-polar GaN grown on bulk GaN will pave the way for future GaN devices with an order of magnitude or more lower threading dislocation density (TDD).

中文翻译：

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通过等离子体辅助分子束外延在体 GaN 上生长高质量的 N 极性 GaN

摘要 '在用于高电子迁移率晶体管 (HEMT) 的体 GaN 上生长 N 极性 GaN 引起了人们的兴趣。当前的 N 极性 HEMT 技术主要是在非原生衬底上生长的器件，由于晶格失配，这些器件具有高密度的位错。直接在非错切 GaN 衬底上生长的 N 极性 GaN 膜在表面上显示出高密度的凹坑和凹坑。这项工作表明，表面杂质在外延生长膜中表面凹坑的形成中起主要作用。通过在生长之前对 GaN 衬底进行紫外线 (UV) O3（臭氧）清洁，并使用 2 nm 相干应变 AlN 层开始生长，在富含金属的条件下生长，我们已经证明了 N 极性 GaN 薄膜具有几乎无坑的表面。该 AlN 起始层 (AIL) 可能会捕获衬底表面上的杂质，从而将衬底表面与外延生长的薄膜分离。事实证明，使用更厚的 AIL（高达 8 nm）可进一步提高薄膜质量和表面形态。本研究中采用的方法生产生长在块状 GaN 上的高质量 N 极性 GaN，将为未来具有一个数量级或更低的穿透位错密度 (TDD) 的 GaN 器件铺平道路。