Surface morphology, structural and optical properties of polar and non-polar ZnO thin films : A comparative study

The polar and non-polar ZnO thin films were fabricated on cubic MgO (1 1 1) and (0 0 1) substrates by plasma-assisted molecular beam epitaxy. Based on X-ray diffraction analysis, the ZnO thin films grown on MgO (1 1 1) and (1 0 0) substrates exhibit the polar c-plane and non-polar m-plane orientation, respectively. Comparing with the c-plane ZnO film, the non-polar m-plane ZnO film shows cross-hatched stripes-like morphology, lower surface roughness and slower growth rate. However, low-temperature photoluminescence measurement indicates the m-plane ZnO film has a stronger 3.31 eV emission, which is considered to be related to stacking faults. Meanwhile, stronger band tails absorbance of the m-plane ZnO film is observed in optical absorption spectrum.