Two dimensional homoepitaxial growth of high quality ZnO epilayers was achieved by chemical vapor deposition
techniques without a buffer layer. We report on the optical and structural properties of these epilayers with particular
focus on the polarity of the surface of the substrate. Photoluminescence spectra exhibit strong dependence of the bound
exciton recombinations on the termination of the substrate. This is particularly pronounced in the large variety of
transition lines in the O-face terminated sample with values for the full width at half maximum as low as 80μeV. Cross-sectional
micro Raman spectroscopy and high resolution transmission electron microscopy reveal the presence of strain
in the epilayer grown on O-face ZnO by a shift of the non-polar E2(high) mode and a variation in the lattice constant
ratio. Still, the crystal quality of the films is further increased compared to the substrate, which is shown be a half-width
of 17" of the XRD rocking curve in both epilayers on Zn-face and O-face terminated ZnO substrate.
We report on the hetero- and homoepitaxial growth of ZnO thin films by the chemical vapor deposition technique. We
compare the results obtained on sapphire substrates, on GaN-templates on sapphire substrates and on silicon (111)
substrates. Even under optimized growth conditions with the insertion of buffer layers the films tend to grow 3-dimensionally. However, also ZnO substrates, expected to be the best choice, need to be prepared before being used in
the epitaxial growth. After mechanical polishing of the ZnO substrates we employed a high temperature annealing step
which produced atomically flat surfaces and removed all of the surface and subsurface damage. Thereafter, the two
dimensional epitaxial growth was achieved without an additional buffer layer. The substrate had a rocking curve full
width at half maximum of 27" which can be compared with that of the film of 22". The films had superior band edge
luminescence as compared to the substrate for which the green luminescence band was dominating.
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