Sie können Bookmarks mittels Listen verwalten, loggen Sie sich dafür bitte in Ihr SLUB Benutzerkonto ein.
Medientyp:
E-Artikel
Titel:
Structure, Optical and Electrical Properties of the High Doped ZnO Thin Films Deposited By RF Magnetron Sputtering of Powder Target in Methane Ambient
Beschreibung:
<jats:p> The ZnO thin films were deposited by RF-magnetron sputtering of ZnO powder target using pure argon, argon with hydrogen and argon with methane as reactive gas. Surface morphology and crystalline structure of the films were studied by SEM, XRD and XRR techniques. Chemical composition and optical properties were investigated by SIMS, Raman scattering spectroscopy (RSS), PL spectroscopy and spectral ellipsometry. Electrical measurements were performed on the ZnO films deposited on SiO<jats:sub>2</jats:sub>-Si and silicon wafers n- and p-type with Ni contacts by TLM, IV, CV characteristics, admittance spectroscopy, Van der Pauw and Hall methods. It was found that growth morphology, crystalline structure, optical and electrical properties of the films are strongly affected by adding methane to argon during the deposition process. Adding of methane resulted in a destruction of hexagonal phase texture and considerable increase a size of ZnO nanocrystallites (from 50 nm for argon to 200 nm for argon/methane working gas). SIMS measurements demonstrated that methane promoted hydrogen incorporation into the ZnO film that was more than an order of magnitude larger in comparison with adding molecular hydrogen in the gas mixture at the same concentration. Adding of methane resulted in a high energy shift of near band edge ultraviolet photoluminescence band, quenching of deep level emission in the visible spectral range and increase of optical band gap from 3.24 to 3.45 eV. The strongest effect of methane has been found for electrical resistivity that reduced by 3 orders of magnitude in comparison with films deposited in pure argon. Additionally, electrical conductance of the ZnO film deposited at high methane concentration does not depend on measurement temperature. Hall method with combination with Van der Pauw resistivity measurements shows: strong n-type doping of the film; donor concentration more than 10<jats:sup>20</jats:sup> cm<jats:sup>-3</jats:sup> slightly depending on methane concentration; maximum electron mobility about 7 cm<jats:sup>2</jats:sup>/V s. The direct comparison of resistivity and donor concentration of the films deposited using methane and molecular hydrogen as doping precursors has demonstrated that doping efficiency of methane is about an order of magnitude larger than that of molecular hydrogen under similar deposition conditions. On the other hand, methane addition in working gas resulted in an intensity decrease of the E2L (100 cm<jats:sup>-1</jats:sup>) and E2H (438 cm<jats:sup>-1</jats:sup>) lines in the RSS that can be associated with some disturbance of the ZnO structure. Additionally a peak at 71 cm<jats:sup>-1</jats:sup> was observed in some films that can be related to the metallic Zn. The possible mechanisms of the ZnO film formation, nature of the doping and electron transport mechanisms will be discussed. </jats:p>