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

Comparative study of group-II alloying effects on physical property of ZnGaO transparent conductive films prepared by RF magnetron sputtering

“…It is suggested that these XRD results can be closely related to the difference in the ionic radii between Zn 2+ (0.06 nm) and the group-II elements, Be 2+ (0.027 nm), Mg 2+ (0.057 nm), Ca 2+ (0.10 nm), and Sr 2+ (0.118 nm), as plotted in Fig. 2(b) [20]. That is to say, when Be, Ca, or Sr atoms with much smaller or larger ionic radius than Zn 2+ host ion are incorporated into ZnXGaO film, these atoms may not efficiently substitute the Zn sites, remaining at defect sites such as interstitials and grain boundary and/or forming micro-clusters.…”

“…Whereas, in Fig. 3(b), Mg 2p XPS spectrum, only well-defined Mg-O binding energy peak is observed at 50.4 eV [20] without any trace attributed to the Mg-Mg bond, indicating that most of the Mg ions doped into the ZnMgGaO film efficiently replace Zn host ion sites. The above observations strongly support that for the alloyed films, a large difference in ionic size between host atom and alloying element can significantly hinder the substitution of alloying element into host atom site, showing a good consistency with XRD results.…”

“…As shown in Figs. 3(a), (c), and (d), the binding energy spectra of Be 1s , Ca 2p , and Sr 3d core levels are clearly deconvoluted into two Gaussian peaks, which can be assigned to the metal-metal bond and the metal-oxygen bond [20,24], respectively, suggesting the co-existence of metal oxide and metallic species in these films. Furthermore, the binding energy peak corresponding to the metal-metal bond is enhanced in proportional to the mismatch of ionic radii between Zn host ion and doped element and ultimately, the metallic Sr-Sr bonding peak becomes more dominant than the Sr-O bonding peak in Sr 3d XPS spectrum, Fig.…”

“…The ceramic targets were prepared by a conventional solid state reaction method, which the mixture made from high purity ZnO (99.99%), Ga 2 O 3 (99.99%), and group-II oxide (BeO, MgO, CaO, SrO: 99.99%) powders was pressed using a cold isostatic press (CIP) and sintered at 950°C for 6 h in furnace. Group-II element and Ga concentrations in targets were chosen as 10 at.% and 4 at.%, respectively, which resulted in the optimum electrical and optical properties in our previous reports [20,21]. The sputtering chamber was initially evacuated down to a pressure of less than 5 Â 10 À6 Torr and then the chamber pressure was maintained at 5 m Torr during the sputtering process by flowing Ar gas at a constant rate of 40 sccm.…”

“…Cao et al [19] also reported a similar result that the optical band-gap of ZnCaO films grown by pulse laser deposition (PLD) could be continuously modulated from 3.28 eV to 3.81 eV with increasing the Ca content from 0 to 22.4 at.%. In our previous work [20], Sr was suggested to be one possible dopant to extend the band gap of ZnO, showing that optical band-gap of the sputter grown Sr-doped ZnAlO film can be widened to 3.46 eV with Sr doping of 10 at.%. Nevertheless, there are only few reports on the donor doping of the ZnO films alloyed with group II elements and to the best of our knowledge, no comparative study on the doping effects of group-II elements into the ZnGaO film exists.…”