Growth and characterization of group-II-alloyed ZnAlO UV-range transparent conductive films prepared by RF magnetron sputtering

•Be most efficiently increases the Eg ∼3.8 eV but results in high ρ = ∼0.5 Ωcm.•Mg resulted in relatively low resistivity ∼7 × 10−4 Ωcm and increase in Eg 3.7 eV.•Metal–metal bonds were observed in the XPS of the ZnAlO (Be, Ca, and Sr) films.•The difference ionic radii resulted in the non-conductive clusters.

ZnAlO films alloyed with various group-II elements (Be, Mg, Ca, Sr) were sputter grown and its effects on the optical and electrical properties of the films were studied. It was observed that addition of Be most efficiently increases the Eg (∼3.8 eV) but results in high resistivity (0.5 Ωcm), while an addition of Mg resulted in a relatively low resistivity (∼7 × 10−4 Ωcm) and moderate increase in Eg (3.7 eV). Other films showed high resistivity (∼1 Ωcm) and relatively low Eg (3.5 eV for ZnSrAlO). It was proposed that the difference in the ionic radii between the alloying elements and the Zn host ion resulted in lattice strain and formation of non-conductive clusters, which would act as the trap centers and scattering centers, reducing the carrier density and the mobility.