Al and Si doping of sputtered ZnO thin films

In this work the effect of Al and Si content on the electrical, optical and structural characteristics of Radio Frequency (RF) sputtered ZnO thin films (~ 150 nrn thick) have been investigated. ZnO:Al and ZnO:Si films were deposited on glass through ZnO and Al targets and ZnO and Si targets co-sputtering, respectively. The Al and Si content have been varied between ~ 1018 cm−3 and ~ 4 × 1021 cm−3, as determined by secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) measurements. The X-ray analysis, in the Θ − 2Θ configuration, revealed a surfactant action of both Si and Al in the films, i.e., a reduction of the absolute stress ⊥ to the c axis from ~ 0.6 − 0.8 GPa to ~ 0.4 GPa and ~ 0.2 GPa for Al and Si doping, respectively. In addition, a corresponding decrease of the root mean square (RMS) of the surface roughness with higher Al and Si content has been observed by Atomic Force Micropscope (AFM) measurements. Finally, the electrical characterization of the ZnO films, performed by room temperature Hall measurements, suggested that the best structural conditions in terms of grain size and absolute stress correspond, as expected, to the minimum resistivity.