Modification of structure and surface morphology in various ZnO facets via low fluence gold swift heavy ion irradiation

Abstract

The influence of low fluence high‐energy ion irradiation on the modification of the ZnO surface structure and optical properties has been studied. ZnO samples of various orientations, namely, c‐plane (0001), a‐plane (11–20) and m‐plane (10–10), have been implanted with 30‐MeV Au ions with fluences ranging from 5 × 109 to 5 × 1011 cm−2. Rutherford backscattering spectrometry in the channelling mode (RBS‐C) and Raman spectroscopy has shown the distinct damage accumulation in the irradiated surface layer about 1 μm depending on the ZnO facet being to larger extent evidenced in the m‐plane ZnO. Contrary, the a‐plane ZnO has been exhibited the lowest Zn disorder. Using atomic force microscopy (AFM), a complex morphology was detected on the irradiated samples containing grains and exhibiting increased roughness, both growing with the Au implantation fluence mainly in m‐plane ZnO. Positron annihilation spectroscopy (PAS) has shown distinct defect accumulation at the Au‐ion fluence of 5 × 1011 cm−2, where RBS‐C and Raman spectroscopy indicated sudden disorder increase in the irradiated layers, probably the creation of more complex clusters of Zn and O vacancies 4VZn + 8VO initiated in connection with an overlap of individual ion impacts. Photoluminescence measurements have shown a distinct near‐band‐edge (NBE) luminescence, developing with the increasing Au‐ion fluence in various ZnO orientations. The m‐plane ZnO had the most progressively suppressed NBE in comparison with the other orientations.