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Chemical nature of N-ions incorporated into epitaxial ZnO films


  • Dedicated to Dieter Schmeißer on the occasion of his 60th birthday


Efficient p-type doping of zinc oxide (ZnO) is hindered on the one hand by the strong native n-type doping of the ZnO, on the other hand, compensation effects (defect generation due to p-doping) tend to preserve the n-type doping. Incorporation of nitrogen is proposed as a promising method to achieve p-type ZnO, because the ionic radii of nitrogen and oxygen are comparable. Therefore, nitrogen atoms can replace oxygen. Nevertheless, a reliable and stable p-doping is still an unmatched challenge. This work will focus on the chemical nature of nitrogen implanted by ion irradiation into metal-organic MBE grown ZnO layers on sapphire substrate. The incorporated nitrogen was investigated by photoelectron spectroscopy using synchrotron radiation (PES) and monochromatised Al Kα (mXPS), and near edge X-ray absorption spectroscopy (NEXAFS). The preparation conditions were varied for preferential incorporation of the different nitrogen species. The three main N1s-PES components were assigned to different nitrogen compounds (molecular N2, N[BOND]O bonds and N[BOND]Zn bonds) with the help of NEXAFS data. In addition, the thermal stability of the nitrogen compounds were investigated. These results may lead to an optimisation of the nitrogen implantation process for a better doping efficiency.