High-temperature CVD growth of monocrystalline ZnO layers with hydrocarbons as a reducing agent

本项目旨在研究一种非常简单的基于cvd的高质量ZnO层的高温生长工艺。这些氧化锌层可能用于透明电子产品，例如透明场效应晶体管（TTFTs），表面声波滤波器（saw）或化学传感器的基础层。此外，由于ZnO的晶格常数与GaN的晶格常数几乎相同，这些ZnO层可以作为未来倒装芯片型led的GaN结构生长的牺牲衬底层。光电探测器的透明前触点是另一个可能的应用。所建议的生长工艺同时获得了专利（DE 10 2015 209 358 B3 of 2016/02/25），其特点是完全简单，并且大部分无毒的前体材料，如ZnO粉末，被甲烷还原为Zn蒸气，并在氧气流中再氧化。在初步测试中，通过窄的XRD摇摆曲线、非常锐利的PL光谱和低的非故意n型掺杂浓度，在（晶格匹配）衬底上获得了高的晶体质量。进一步的研究旨在了解和控制初始生长阶段，改善均匀性和表面光滑度，避免倾斜颗粒夹杂等缺陷，控制n型掺杂，以及将衬底面积从目前的1 cm²扩大到更大（~ 4 cm²）。此外，还需要测试控制n型掺杂的ZnO层和异质结构带隙较大的MgZnO层的可行性。

This project aims at a very simple CVD-based high temperature growth process for high quality ZnO layers. These ZnO layers might be used in applications like transparent electronics, e.g. transparent field effect transistors (TTFTs), surface acoustic wave filters (SAWs), or base layers for chemical sensors. Furthermore, these ZnO layers might serve as sacrificial substrate layers for the growth of GaN structures for future flip chip-type LEDs, since ZnO has lattice constants almost identical to those of GaN. Transparent front contacts for Photodetectors are another possible application.The suggested growth process, for which meanwhile a patent was granted (DE 10 2015 209 358 B3 of 2016/02/25), is characterized by total simplicity and largely nontoxic precursor materials like ZnO powder, which is reduced to Zn vapour by methane, and re-oxidized in an oxygen stream. In preliminary tests, high crystal quality on (lattice matched) substrates has been obtained in terms of narrow XRD rocking curves, very sharp PL spectra, and low non-intentional n-type dopant concen-tration. Further research aims at an understanding and control of the initial growth phase, im-provement of homogeneity and surface smoothness, avoidance of defects like inclusion of tilted grains, controlled n-type doping, and scaling up to larger substrates areas (~ 4 cm²) from presently 1 cm². Also the feasibility of ZnO layers with controlled n-type doping and MgZnO layers with larger bandgap for heterostructures shall be tested.