Lanthanide Doped Wide Band Gap Semiconductors: Intra-4f Luminescence and Lattice Location Studies

Abstract

Luminescence properties, along with lattice locations of lanthanide implanted into wide band gap semiconductors, are presented in this work. This study focuses on semiconductors with the widest currently known band gap among their group. These are represented by aluminum nitride and cubic boron nitride for the group of III-V nitride semiconductors, as well as diamond and 6H-silicon carbide for the group of carbide semiconductors. The method of choice for doping at this stage is ion implantation, preferably with low ion fluences, thereby keeping implantation damage as low as possible. This also provides that the lanthanides represent impurities, neither altering the hosts properties nor significantly influencing each other. The focus is on a few selected lanthanides, namely thulium and europium, complemented by the use of gadolinium in one case. In a first attempt these systems are characterized by cathodoluminescence spectroscopy, accompanied by lattice location studies of lanthanides in the same host matrices. In the luminescence investigations those systems are identified which are suitable for a crystal field analysis. The aim of this analysis is to identify the local symmetry of the implanted ions.An introduction to the field of lanthanide-doped semiconductors is given in chapter 2, providing an overview of current research trends and characterization techniques. This is accompanied by a critical reflection on the role of radioactive lanthanides and hyperfine measurements in the field of lanthanide-doped semiconductor physics, with respect to the use of radioactive lanthanides in this work.Chapter 3 provides a condensed presentation of the fundamentals of luminescence of triply ionized lanthanides, the emission channeling method and other characterization techniques used in this work. The main focus is on the calculation of the energy matrix to provide the knowledge required to perform a crystal field analysis and to understand the luminescence spectra of lanthanide-doped semiconductors. The presentation of theory is thereby accompanied by selected references to existing literature. Triply ionized lanthanides are classified according to their energy level structure and transition probabilities, with a focus on Eu 3+ , Tm 3+ , and Gd 3+ , used as luminescence probes in this work. For other characterization techniques such as emission channeling and Mössbauer spectroscopy an overview of applicable isotopes is given with a description of the experimental energy spectra.The experimental setups assembled and used in this work are discussed in chapter 4, mainly the CHAPTER 2. INTRODUCTION sources, allowing for a possible application as phosphor illuminators, which are important for the implementation of white light emitters [55,56].The main goal in using lanthanide implanted semiconductors has been the implementation of highly efficient light emitters [57] and solid state lasers [58, 59]. The discovery of new appropriate host matrices is followed by years of studying the physical properties and mechanisms underlyin...