Epitaxial growth of ZnO thin films
|Epitaxial ZnO films were grown by reactive medium-frequency magnetron sputtering. The film in-plane ordering was studied by measuring φ -scans for the ZnO (105) plane. In the case of chemically cleaned substrates and at TS<300 °C the films are polycrystalline without indications of in-plane ordering. The films grown at TS=300-600 °C without target presputtering onto chemically cleaned substrate show 12 peaks. It is characteristic of two types of domains having in-plane orientations with a 30° rotation of the unit cells relative to one another. In contrast, deposition onto oxygen plasma pretreated substrates always results in films whose phi-scans show single-domain in-plane orientation with the a-axis rotated by 30° with respect to the substrate. The single-domain films form even at a substrate temperature of 100°C in wide range of oxygen pressures, and at a growth rate up to 1.2 nm/s. In the RBS/channeling spectrum of the single-domain films (Figure 6), the apparent χ min value at the film/substrate interface (17%) is significantly higher than at the film surface (6%). A peak, clearly visible in the RBS data close to the interface position, suggests the presence of displaced Zn atoms there. It which may be due to a higher density of defects, including misfit dislocations, as resulting from the large lattice mismatch.|
XRD φ -scans of ZnO films grown using the following parameters:
a) no target presputtering, chemical cleaning of the substrate TS=RT (polycrystalline film),
b) 600 °C (two-domain film); target presputtering,
c) additional pretreatment of the substrate with O2 RF plasma , TS=550 °C (single-domain film).
Figure 6. RBS channeled and random spectra of a single-domain epitaxial film.
1. M. Vinnichenko, N. Shevchenko, A. Rogozin, R. Grötzschel, A. Mücklich, A. Kolitsch, and W. Möller: Structure and dielectric function of two- and single-domain ZnO epitaxial films, Submitted to J. Appl. Phys. (2007).