Abstract Here we examined the use of AlN buffer layers of various thicknesses to improve the crystalline quality of nonpolar a -plane GaN ( a -GaN) grown on an r -plane sapphire substrate. Three types of AlN buffer layers were used: sputtered AlN buffer layers (sp-AlNs) with or without annealing, and epitaxially grown AlN buffer layers (ep-AlNs). Buffer layer thicknesses of 30, 90, and 180 nm were used. We found that the surface morphological transitions with increasing thickness were different between the sp-AlNs and the ep-AlNs, and that the sp-AlNs had poorer crystallographic orientations than did the ep-AlNs. Annealing caused marked changes to occur in the surface morphologies and crystallographic orientations of the sp-AlNs; however, the positive effect of annealing was limited because the in-plane crystallographic orientation degraded with increasing layer thickness. The optimal buffer layer was found to be the 30-nm-thick annealed sp-AlN, which was composed of uniformly arranged oval grains with better crystallographic orientation than the other sp-AlNs and annealed sp-AlNs. The crystalline quality of the a -GaN epilayer grown on 30-nm-thick annealed sp-AlN had a narrower X-ray rocking curve–full width at half maximum for both the on- and off-axis planes compared with that grown on any other AlN buffer layers.

中文翻译：

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r面蓝宝石衬底上溅射AlN缓冲层的表征和优化以提高非极性a面GaN的晶体质量

摘要 在这里，我们研究了使用不同厚度的 AlN 缓冲层来改善在 r 面蓝宝石衬底上生长的非极性 a 面 GaN (a -GaN) 的晶体质量。使用了三种类型的 AlN 缓冲层：带或不带退火的溅射 AlN 缓冲层 (sp-AlNs)，以及外延生长的 AlN 缓冲层 (ep-AlNs)。使用了 30、90 和 180 nm 的缓冲层厚度。我们发现随着厚度的增加，sp-AlNs 和 ep-AlNs 的表面形态转变是不同的，并且 sp-AlNs 的晶体取向比 ep-AlNs 差。退火导致 sp-AlNs 的表面形貌和晶体取向发生显着变化；然而，退火的积极影响是有限的，因为面内晶体取向随着层厚度的增加而降低。发现最佳缓冲层是 30 nm 厚的退火 sp-AlN，它由均匀排列的椭圆形晶粒组成，具有比其他 sp-AlN 和退火 sp-AlN 更好的晶体取向。在 30 nm 厚的退火 sp-AlN 上生长的 a -GaN 外延层的晶体质量具有更窄的 X 射线摇摆曲线 - 轴上和离轴平面的半高全宽与生长在任何其他 AlN 缓冲层。