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的高质量氧化锌薄膜高温生长工艺。这些氧化锌层可用于透明电子等应用，例如透明场效应晶体管(TTFT)、表面声波滤光器(SAW)或化学传感器的基层。此外，由于氧化锌的晶格常数与GaN的晶格常数几乎相同，这些氧化锌层可能作为未来倒装芯片型LED生长GaN结构的牺牲性衬底。用于光电探测器的透明正面触点是另一种可能的应用。所提出的生长工艺的特点是完全简单且基本上无毒的前体材料，如氧化锌粉末，被甲烷还原为锌蒸气，然后在氧气中重新氧化。该生长工艺同时获得了专利(DE 10 2015 209 358 B3,2016/02/25)。在初步测试中，在(晶格匹配的)衬底上获得了高质量的晶体，其X射线衍射摇摆曲线窄，荧光光谱非常尖锐，非故意n型掺杂浓度很低。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，避免缺陷，如倾斜的晶体夹杂，受控的n型掺杂，并扩大到更大的衬底面积(~4 cm2)，从目前的1 cm2。同时，对n型掺杂控制的氧化锌层和带隙较大的氧化镁异质结薄膜的可行性进行了测试。

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.