Heteroepitaxial growth behavior of Mn-doped ZnO thin films on Al2O3 (0001) by pulsed laser deposition

Heteroepitaxial growth behavior of Mn-doped ZnO thin films $({\mathrm{Zn}}_{\text{1−x}}{\mathrm{Mn}}_x\mathrm{O})$ on ${\mathrm{Al}}_2{\mathrm{O}}_3$ (0001) substrates by pulsed laser deposition was investigated particularly as a function of Mn content $\text{(0.00⩽x⩽0.35)}$ using synchrotron x-ray scattering and atomic force microscopy. The undoped ZnO film was grown epitaxially with a $\text{30°}$ rotation of ZnO basal planes with respect to the ${\mathrm{Al}}_2{\mathrm{O}}_3$ substrate while having a small amount of grains with another epitaxial relationship, i.e., the hexagon-on-hexagon growth. A small amount of Mn doping $\text{(x=0.05)}$ not only greatly improved the atomic alignment both in the in-plane and in the out-of-plane directions, but also led to a singly oriented film by totally suppressing the hexagon-on-hexagon growth. With further incorporation of Mn into ZnO beyond that content, the epitaxial nature again deteriorated. The superior epitaxial growth of the film with an optimum Mn content is attributed to the formation of much larger grains in it. In addition, our Mn-doped ZnO thin films showed a paramagnetic behavior.