Influence of the nanoscale structural features on the properties and electronic structure of Al-doped ZnO thin films: An X-ray absorption study

• Published in: Solar energy materials and solar cells Vol. 95; no. 8; pp. 2341 - 2346
• Main Authors: Jullien, M., Horwat, D., Manzeh, F., Escobar Galindo, R., Bauer, Ph, Pierson, J.F., Endrino, J.L.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.08.2011; Elsevier
• Subjects: Aluminum; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Deposition; Electrical properties of specific thin films; Electrical resistivity; Electronic structure; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Flow rate; Homologous phase; Nanomaterials; Nanostructure; Other inorganic semiconductors; Physics; Resistivity; Thin films; Transparent conducting oxide; XANES; Zinc oxide; Electronic structure; XANES; Homologous phase; Resistivity; Transparent conducting oxide; Stoichiometry; Electrical conductivity; Doped materials; Layered materials; Nanostructures; Fabrication property relation; Conducting materials; Thin films; Magnetrons; Cathode sputtering; Aluminium additions; Zinc oxide; Reactive sputtering; Microstructure; Transparent material; Ultraviolet visible spectrometry
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2011.04.003

Transparent Al-doped ZnO thin films were deposited by reactive magnetron sputtering with different oxygen flow rates. The electronic resistivity, measured by the 4 point-probe method, is very sensitive to the sample position relative to the magnetron axis: the closer the magnetron from the axis the higher the resistivity. This is more pronounced for the films deposited under higher oxygen flow rate. Neither Rutherford backscattering spectroscopy nor Zn–K edge X-ray absorption near-edge structure (XANES) analyses evidenced any change in chemical composition such as a measurable variation of the oxygen stoichiometry. XANES at the Al–K and O–K edges show that (i) a portion of the aluminum atoms get positioned in octahedral conformation with oxygen, consistent with the formation of an Al 2O 3(ZnO) m nanolaminate structure, (ii) the films exhibit relaxed O-terminated (0 0 0 1) surfaces with a higher density of empty states in more resistive samples. These two findings are believed to play a significant role on the electrical measurements by dopant deactivation and by creating an insulating barrier at the film surface, respectively. [Display omitted] ► Nanoscale structural features of Al-doped ZnO thin films were addressed by XANES. ► XANES at the Al–K edge indicates the formation of Al 2O 3(ZnO) m homologous phase. ► XANES at the O–K edge indicates a relaxation between the extreme surface layers. ► Optical, electrical properties and crystallinity are sensitive to the nanoscale features.