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

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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.