The integration of GaN on Si as large scale substrates still faces many hurdles. Besides the large difference in the lattice constant and the high thermal mismatch existing between GaN and Si, spiral hillock growth phenomena are common problems in the development of thick GaN layers. In this work, hexagonal hillocks were observed on GaN/AlGaN high-electron-mobility transistor heterostructures grown on Si(111) by metal-organic chemical vapor deposition. The presence of these morphological and structural defects is attributed to the presence of localized contamination at the AlN/Si interface. These carbon-based defects cause highly defective regions in the AlN seed layer, which propagate through all the AlGaN buffer layers inducing the formation of V-shaped pits at the AlGaN interfaces. In hillock regions of the wafers, Raman spectroscopy indicates disturbed two-dimensional electron gas characteristics resulting from GaN/AlGaN interface roughness and a decreased amount of free carriers in the potential well. Energy-dispersive x-ray spectroscopy reveals Ga accumulation inside the V-pits and in nanopipes below, which is responsible for defective areas and the increased GaN growth rate resulting in hillock formation. Photoluminescence measurements confirm the presence of Ga-rich material reducing the inherent gallium vacancy concentration. Here, the reduced amount of Ga-vacancies acting as a shallow acceptor suppresses the ultraviolet luminescence band from donor–acceptor pair transition.

中文翻译：

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碳相关小丘的形成及其对在 Si(111) 上生长的 GaN/AlGaN 异质结构的光电特性的影响

将 GaN 集成在 Si 上作为大规模衬底仍然面临许多障碍。除了 GaN 和 Si 之间存在较大的晶格常数差异和高热失配外，螺旋小丘生长现象是厚 GaN 层开发中的常见问题。在这项工作中，通过金属有机化学气相沉积在 Si(111) 上生长的 GaN/AlGaN 高电子迁移率晶体管异质结构上观察到六边形小丘。这些形态和结构缺陷的存在归因于 AlN/Si 界面处局部污染的存在。这些基于碳的缺陷会导致 AlN 种子层中的高度缺陷区域，其传播通过所有 AlGaN 缓冲层，从而导致在 AlGaN 界面形成 V 形凹坑。在晶圆的小丘区域，拉曼光谱表明，由于 GaN/AlGaN 界面粗糙度和势阱中自由载流子的数量减少，二维电子气特性受到干扰。能量色散 X 射线光谱揭示了 V 凹坑内和下方纳米管中的 Ga 积累，这是造成缺陷区域和 GaN 生长速率增加导致小丘形成的原因。光致发光测量证实了富镓材料的存在，降低了固有的镓空位浓度。在这里，作为浅受主的 Ga 空位的减少抑制了来自施主-受主对跃迁的紫外发光带。能量色散 X 射线光谱揭示了 V 凹坑内和下方纳米管中的 Ga 积累，这是造成缺陷区域和 GaN 生长速率增加导致小丘形成的原因。光致发光测量证实了富镓材料的存在，降低了固有的镓空位浓度。在这里，作为浅受主的 Ga 空位的减少抑制了来自施主-受主对跃迁的紫外发光带。能量色散 X 射线光谱揭示了 V 凹坑内和下方纳米管中的 Ga 积累，这是造成缺陷区域和 GaN 生长速率增加导致小丘形成的原因。光致发光测量证实了富镓材料的存在，降低了固有的镓空位浓度。在这里，作为浅受主的 Ga 空位的减少抑制了来自施主-受主对跃迁的紫外发光带。