Transparent and conductive ZnO:Al films prepared by reactive mf magnetron sputtering at high deposition rate

Multifunctional films with high transmittance in the visible spectral range and metal-like electrical conductivity can be obtained by doping of wide band-gap semiconductive materials (e.g. oxides of indium, tin, zinc, their alloys etc.). These transparent and conductive oxide (TCO) films are used e. g. as transparent electrodes in flat panel displays and solar cells, for electrochromic coatings on architectural glazing and in other electro opical devices, as antistatic coatings on cathode ray tubes as well as transprent heat mirrors on solar cellectors, incandescent bulbs and glass windows. In this study, the reactive midfrequency (MF) magnetron sputtering of transparent and conductive ZnO:Al layers has been investigated. High quality ZnO:Al films were prepared by reactive mid-frequency magnetron sputtering (Leybold TwinMag TM) at deposition rate of aprox. 9 nm/s and substrate temperature of 100 ...200 °C. ZnO:Al films prepared by this technique exhibit low resistivity of 300 µ cm at 200 °C substrate temperature and 480 µ cm at 100 °C substrate temperature (film thickness of 500 nm). The optical, electrical and structural properties of these films have been investigated by means of optical spectroscopy (UV-IR), varible angle spectroscopic ellipsometry, X-ray diffraction, atomic formce microscopy, Hall mobility and conductivity measurements. Electron probe micro analysis and secondary ion mass spectroscopy has been used for chemical characterization.