Nanostructured surfaces

Effect of implantation of Ho and Nd ions on the physical properties of thin ZnO films
Oberemok O.1, Melnik V.1, Dubikovskyi O.1, Gudymenko O.1, Kosulya O.1, Romanyuk B.1, Kolomys O.1, Sabov T.1, Maksimenko Z.1
1Department of Ion Beam Engineering, V. Lashkaryov Institute of Semiconductor Physics of NAS of Ukraine, 41, prospect Nauky, 03028, Kyiv, Ukraine. 
E-mail: ober@isp.kiev.ua

The large exciton binding energy of 60 meV and wide band gap energy of 3.37 eV at room temperature promote the use of ZnO thin films as a host photonic material in the creation of sensor and light-emitting devices [1]. Ho or Nd doping is a promising method for engineering of ZnO film optical properties due to the large number of energy levels of elements. The incorporation of these elements into the ZnO crystal lattice occurs in the form of the replacement of Zn2+ ions by Ho3+ and Nd3+ ions. The built-in ions have more large radii that leads to distortion of the ZnO structure during annealings. Ion-beam implantation of elements with subsequent thermal treatments is a promising method for controlling the distribution of dopants in the ZnO film. This work is devoted to elucidation of the optical, structural, and phase changes caused by Ho and Nd ion implantation in a ZnO host film. 
Analyzed polycrystalline ZnO films are an array of vertical highly oriented nanorods on the Si (100) surface. It is ascertained that the Ho or Nd ion implantation leads to an improvement in the level of crystallinity of ZnO nanorod arrays. Threshold temperatures for displacement of Ho or Nd dopants outside the nanorods are 750°C and 600°C, respectively. It is shown that the implanted dopants are almost uniform distributed over the ZnO film thickness and accumulate at the SiOx/Si interface at high-temperature annealing. The assumption that neodymium, unlike holmium, has time to oxidize during intergranular diffusion has explained the formation of thinner silicon oxide at the ZnO/Si interface. Thus, the use of Ho and Nd impurities as an activator and sensitizer in light-emitting ZnO nanostructures requires the use of thermal activation modes in which both dopants will remain in ZnO nanocrystals. 

1.	Melnik, V. P. et al. Formation and Transient Photovoltaic Properties of ZnO/Si Isotype Heterojunctions by Magnetron Sputtering // Nanomaterials and Nanocomposites, Nanostructure Surfaces, and Their Applications. Springer Proceedings in Physics, vol 246. Springer, Cham (2021).