Self-texture in the initial stages of ZnO film growth

X-ray absorption spectroscopy has been used to investigate the self-texture of ZnO films grown on Si(100) (lattice-mismatched substrate) by single-source chemical vapor deposition (SS-CVD) using Zn4O(acetate)(6) as precursor. For this system nonepitaxial growth of polycrystalline, c-axis oriented films can be controlled by addition of a water ambient during the deposition for a large variety of substrates. Angle dependent near edge X-ray absorption fine structure spectroscopy (NEXAFS) was used to study the orientation of the adsorbent molecules as a function of both water ambient used during the deposition and film thickness. The onset of self-structuring under optimum growth conditions (highest water pressure, PH2O = 5 x 10(-4) mbar) is found to occur at film thicknesses on the order of 50 Angstrom. The role of the water ambient during the film deposition is discussed using a kinetic model in which lattice stabilization due to filling of oxygen vacancies promotes the film crystallization. The model is used to explain the measured changes in the atomic environment of the oxygen atoms in the deposited ZnO films with variation in ambient water used. The interfacial restrictions in nonepitaxial CVD film growth are discussed. Our results indicate that in addition to structural restrictions due to lattice mismatch the chemical reactivity of the substrate material clearly must be considered.