Change in polarity of zinc oxide films grown on sapphire substrates without insertion of any buffer layer

We have investigated the polarity of zinc oxide (ZnO) and Al-doped ZnO films grown on (11^¯₂0) and (0001) sapphire substrates, using coaxial impact collision ion scattering spectroscopy. The films grown by pulsed laser deposition with a nominally undoped ZnO ceramic target had a (000^¯₁) surface, whereas the films prepared with a 1 mol% Al-doped ZnO ceramic target had a (0001) surface. The usage of Al-doped and undoped targets caused no difference in the in-plane lattice orientation. Electron microscope observations revealed that polarity change due to doping occurred without the formation of any interfacial phase between ZnO and sapphire.