X-ray absorption spectroscopy study of thin ZnO films grown by single source CVD on Si(100)

In situ X-ray absorption spectroscopy analysis of early states of ZnO film growth on Si(100) by single source chemical vapor deposition (CVD) has been performed using basic zinc acetate as precursor. A high concentration of carbon is detected at the interface, which decreases with increasing film thickness (similar to 2 nm thickness), and as expected there is some oxidization of the Si surface. This is explained by the chemical nature of the immediate surface upon which the deposition takes place, varying from a reactive, clean Si surface to a less reactive, mixed oxide layer after successive deposition steps. On the latter surface, the decomposition fragments are believed to be more volatile and thus the resulting film contains less carbon contamination. The results confirm that the tetrahedral core of the central oxygen atom with four neighboring zinc atoms, which reassembles the structure in solid ZnO, is kept intact upon decomposition of the precursor on the heated Si(100) (400 degrees C) substrate. However, no long range orientation of the ZnO tetrahedrons was found, indicating that the resulting ZnO film has no preferred crystalline structure for the film thickness investigated here (similar to 2 nm).