Optical and structural properties of homoepitaxial ZnO

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.