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 (CH 4 ) 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 highresolution 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.

The growth of high-quality single-crystalline zinc oxide (ZnO) layers on silicon (Si(111)) substrates with an intermediate aluminum nitride (AlN) nucleation layer was investigated. The ZnO layers were grown using a methane (CH 4 )-based chemical vapor deposition (CVD) growth process, while the AlN nucleation layers were grown by metal−organic vapor-phase epitaxy (MOVPE). We investigate the influence of nucleation layer thickness and growth temperature on the final ZnO layer quality and also vary the ZnO growth parameters to obtain smooth surfaces and the best crystal quality. The ZnO layers were extensively characterized by various methods such as atomic force microscopy (AFM), high-resolution X-ray diffraction (HRXRD), electron backscatter diffraction (EBSD), and scanning/transmission electron microscopy (SEM/TEM). We find that AlN nucleation layers grown at 1150 °C for 15 min yielded the best final ZnO layer quality with fully c oriented ZnO layers free of rotational domains. In HRXRD ω scans full width of half maximum (fwhm) values of about 710 and 1240 arcsec for the (0002) and (101̅ 2) reflections, respectively, were achieved. Dislocation densities of ρ edge = 1.6 × 10 10 and ρ screw = 9.1 × 10 8 cm −2 and a lateral coherence length (LCL) of L ∥ = 300 nm are deduced, values which are among the best reported in the literature for ZnO layers grown on Si(111). Additionally, we carried out high-resolution photoluminescence (PL) measurements at liquid-helium and room temperatures, which also prove low defect densities. The low-temperature PL spectra were also used to study the stress within the ZnO layer and compared to HRXRD stress measurements. Both measurements confirm a stress reduction in the ZnO layer with increasing thickness.