Department of Electronic Systems, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway. Department of Engineering and Applied Sciences, Sophia University, 102-8554, Tokyo, Japan.
Nanotechnology. 2019 Jan 4;30(1):015604. doi: 10.1088/1361-6528/aae76b. Epub 2018 Oct 30.
We report on the self-assembled growth of high-density and vertically-oriented n-doped GaN nanocolumns on graphene by radio-frequency plasma-assisted molecular beam epitaxy. Graphene was transferred to silica glass, which was used as the substrate carrier. Using a migration enhanced epitaxy grown AlN buffer layer for the nucleation is found to enable a high density of vertical GaN nanocolumns with c-axis growth orientation on graphene. Furthermore, micro-Raman spectroscopy indicates that the AlN buffer reduces damage on the graphene caused by impinging active N species generated by the radio-frequency plasma source during the initial growth stage and nucleation of GaN. In addition, the grown GaN nanocolumns on graphene are found to be virtually stress-free. Micro-photoluminescence measurements show near band-edge emission from wurtzite GaN, exhibiting higher GaN bandgap related photoluminescence intensity relative to a reference GaN bulk substrate and the absence of both yellow luminescence and excitonic defect emission. Transmission electron microscopy reveals the interface of GaN nanocolumns on graphene via a thin AlN buffer layer. Even though the first few monolayers of AlN on top of graphene are strained due to in-plane lattice mismatch between AlN and graphene, the grown GaN nanocolumns have a wurtzite crystal structure without observable defects. The results of this initial work pave the way towards realizing low-cost and high-performance electronic and optoelectronic devices based on III-N semiconductors grown on graphene.
我们报告了在射频等离子体辅助分子束外延条件下，自组装生长在石墨烯上的高密度、垂直取向的 n 掺杂 GaN 纳米柱。石墨烯被转移到了二氧化硅玻璃上，后者被用作衬底载体。使用迁移增强外延生长的 AlN 缓冲层进行成核，被发现可以在石墨烯上实现高密度的垂直 GaN 纳米柱，其 c 轴生长方向一致。此外，微拉曼光谱表明，AlN 缓冲层减少了射频等离子体源在初始生长阶段和 GaN 成核过程中产生的活性 N 物种对石墨烯的损伤。此外，在石墨烯上生长的 GaN 纳米柱几乎没有应力。微光致发光测量显示了纤锌矿 GaN 的近带边发射，其与参考 GaN 体衬底相比，GaN 带隙相关光致发光强度更高，且不存在黄带发光和激子缺陷发射。透射电子显微镜通过薄的 AlN 缓冲层揭示了 GaN 纳米柱在石墨烯上的界面。尽管由于 AlN 和石墨烯之间的面内晶格失配，石墨烯顶部的前几层 AlN 处于应变状态，但生长的 GaN 纳米柱具有无观测到缺陷的纤锌矿晶体结构。这项初步工作的结果为在石墨烯上生长的 III-N 半导体实现低成本、高性能的电子和光电子器件铺平了道路。
