Dependence of Ga-doped ZnO thin film properties on different sputtering process parameters: Substrate temperature, sputtering pressure and bias voltage
This paper reports on the effects of different sputtering deposition process parameters (substrate temperature,
sputtering pressure and bias voltage) on the electrical, optical, structural and morphological properties of
gallium-doped ZnO (ZnO:Ga) of ~1 μm thick. These highly transparent and conductive films were deposited
on glass surfaces by d.c. pulsed magnetron sputtering from a GZO (ZnO(95.5):Ga2O3(4.5)) ceramic target in an
argon atmosphere. X-ray diffraction experiments show that all films have a hexagonal wurtzite structure with
the [001] preferred crystallographic direction, and themorphology of the films (obtained fromscanning electron
microscope analysis) is sensitive to the process parameters. All ZnO:Ga films have an average transmittance
above 80% in the visible region, and the lowest electrical resistivity of 3.03 × 10−4 Ω·cm was achieved for the
sample submitted to the lowest bias voltage (−40 V), which corresponds to a carrier concentration and a carrier
mobility of 6.99 × 1020 cm−3 and 29.49 cm2 V−1 s−1, respectively. A high substrate temperature, high sputtering
pressure and lownegative bias voltage (within the range of studied parameters) proved to be very promising on
obtaining optimized ZnO:Ga films, ensuring suitable properties for application as transparent electrodes in photovoltaic
cells.The authors acknowledge the funding from the Portuguese Innovation Agency (AdI), project reference WinDSC-21539, co-funded by FEDER/POFC