Research of ZnO films implanted by Yb on PIRX beamline
SOLARIS users’ study conducted on the PIRX (former PEEM/XAS) beamline was aimed at understanding properties and developments of defects that are formed in zinc oxide matrix implanted by ytterbium and subsequent annealing. Studies show the potential of X-ray absorption spectroscopy as a tool for testing whether considered defects are isolated or whether clustering of defects is occurring. It was shown that, along with isolated defects, the donor-acceptor (mVZn-nVO ) complexes do exist even in the virgin sample. Their number increases in the implanted and annealed samples, affecting the transport properties of the films under study. It also indicated that the implantation and subsequent annealing have an important influence on the native point defect complexes in ZnO.
Introduction of defects
One way to influence the properties of a material is to create defects, or agglomerates, in its structure. Such introduction of defects into the material can not only change its electronic structure, but also its optical properties. With a better understanding of doping and annealing processes, we can increase the number of available active sites in the material under study, and thus directly affect optoelectronic performance. Discoveries in this area are leading to better, more efficient semiconductor devices used as a down-converter material in photovoltaics.
Research on materials used in optics and optoelectronics was conducted by scientists from Warsaw. It has been shown that along with single point defects, such as oxygen vacancies or zinc vacancies that are often associated with green/red luminescence, vacancy complexes exist in ion implanted and then annealed ZnO:Yb samples. These complexes can be electrically active and may significantly modify the electrical properties of the host matrix. This suggestion was confirmed by previous Hall measurements indicating that resistivity of annealed ZnO:Yb film with fluence 5e15 ions/cm2 decreases by about one order of magnitude as compared to one with fluence 5e14 ions/cm2.
SOLARIS users used a technique available on the PIRX beamline, they measured and analyzed near edge X-ray absorption fine structure (NEXAFS) spectra of the aforementioned system, taking into account the polarization effect of synchrotron radiation The results revealed a strong polarization of the sample surface dependent on the polarization vector of the synchrotron radiation.
Prof. Iraida Demchenko, a corresponding author of the publication, says about the results of their work:
„In this work, we studied virgin and Yb-implanted epitaxial ZnO films employing X-ray absorption technique available at the beamline 'PEEM/XAS' at National Synchrotron Radiation Centre SOLARIS. Analysis of experimental spectra, together with theoretical simulations, confirmed the presence of donor-acceptor complexes (mVZn - nVO, m = 1,4; n = 1,2) in the samples under study. It was also concluded that oxidation state of Yb in ZnO is 3+, and that Yb are surrounded by oxygen in pseudo octahedra. Different doses of implantation disturb the orientation of these octahedra with respect to the growth of direction of film that was observed from an inversion of the polarization dependence for samples with different Yb fluences. Ultimately, our study aims to deepen our understanding of implantation-induced defects, their interaction with host matrix defects, and efforts to eliminate, manipulate and/or reorganize these defects via annealing to achieve good quality material.”
The entire text of the publication is available at the link –
Written by Iraida Demchenko, Kinga Wróbel, Marcin Zając