Chemical Vapor Deposition Growth of Zinc Oxide on Sapphire with Methane: Initial Crystal Formation Process
Chemical Vapor Deposition Growth of Zinc Oxide on Sapphire with Methane: Initial Crystal Formation Process
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DOI：
10.1021/acs.cgd.9b00181
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发表时间：
2019-09-01
影响因子：
3.8
通讯作者：
Thonke, Klaus
中科院分区：
文献类型：
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作者：
Mueller, Raphael;Huber, Florian;Thonke, Klaus
采用基于高温化学气相沉积 (CVD) 的新型高质量氧化锌 (ZnO) 层生长工艺，研究了具有氮化铝成核层的蓝宝石衬底上异质外延生长的初始阶段。使用不同供应的锌蒸气生长了一系列样品，可以通过用于还原 ZnO 粉末的前体气体甲烷 (CH4) 的量轻松控制。在衬底区域中，锌蒸气被纯氧再氧化，这最初导致在衬底上形成 ZnO 岛，并且需要更长的生长持续时间才能获得所需的高度结晶的 ZnO 层。为了确定该初始层形成过程的细节，使用了原子力显微镜和扫描电子显微镜。我们发现，ZnO 微晶的聚结速度非常快，仅在 10 分钟的生长时间后就形成了光滑且封闭的层。层形成早期阶段的电子背散射衍射测量显示 ZnO 微晶具有完美的 c 取向。此外，高分辨率 X 射线衍射测量支持 ZnO 层的完美排列，并显示晶体质量随着生长时间的急剧增加。低温光致发光 (PL) 测量也证明了晶体质量的提高，其中光谱显示 ZnO 微晶中已有的供体束缚激子的锐线。 PL 光谱还清楚地表明，当 ZnO 微晶开始聚结但聚结后很快退火时，形成基面堆垛层错的趋势相当高。
Using a new high-temperature chemical vapor deposition (CVD)-based growth process for high-quality zinc oxide (ZnO) layers, the initial stages for heteroepitaxial growth on sapphire substrates with an aluminum nitride nucleation layer was investigated. A series of samples were grown with various supplies of zinc vapor, which can easily be controlled by the amount of the precursor gas methane (CH4) used to reduce the ZnO powder. In the substrate region, the zinc vapor was reoxidized by pure oxygen, which initially led to the formation of ZnO islands on the substrate, and for longer growth duration to the desired highly crystalline ZnO layers. To determine the details about this initial layer formation process, atomic force microscopy and scanning electron microscopy were used. We find that the ZnO microcrystals coalesce very fast and form a smooth and closed layer after a growth time of 10 min only. Electron backscatter diffraction measurements on this early stage of the layer formation show a perfect c-orientation of the ZnO microcrystals. Also high- resolution X-ray diffraction measurements support the perfect alignment of the ZnO layer and show a drastic increase in crystal quality over growth time. This increase in crystal quality is also demonstrated by low-temperature photoluminescence (PL) measurements, in which the spectra show sharp lines for the donor-bound excitons already for the ZnO microcrystals. The PL spectra also show clearly that the tendency of forming basal plane stacking faults is quite high when the ZnO microcrystals are starting to coalesce but anneal out very fast after coalescence.