Effects of substrate on the structure and orientation of ZnO thin film grown by rf-magnetron sputtering

X-ray diffractions, Nomarski microscopy, scanning electron microscopy, and photoluminescence have been used to study the effects of substrate on the structure and orientation of ZnO thin films grown by rf-magnetron sputtering. GaAs(001), GaAs(111), Al2O3(0002) (c-plane), and Al2O3(1102) (r-plane) wafers have been selected as substrates in this study. X-ray diffractions reveal that the ZnO film grown on GaAs(001) substrate is purely textured with a high c-axis orientation while that grown on GaAs(111) substrate is a single ZnO(0002) crystal; a polycrystalline structure with a large-single-crystal area of ZnO(0002) is obtained on a c-plane Al2O3 substrate while a ZnO(1120) single crystal is formed on an r-plane Al2O3 substrate. There is absence of significant difference between the photoluminescence spectra collected from ZnO/GaAs(001), ZnO/GaAs(111), and ZnO/Al2O3(0002), while the photoluminescence from ZnO/Al2O3(1102) shows a reduced intensity together with an increased linewidth, which is, likely, due to the increased incorporation of native defects during the growth of ZnO(1120)