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Characterization and elemental analysis of nano- and microdimensional structures using PIXE and RBSDipl.-Phys. Christoph Meinecke, Dr. Daniel Spemann In collaboration with the divisions of Semiconductor Physics and Superconductivity and Magnetism, respectively, ZnO thin films, nominally undoped, alloyed with Mg, P, Co and Ga grown epitaxially on c-plane sapphire by pulsed laser deposition (PLD) were investigated. In order to determine the elemental composition as well as the film thicknesses the films were analysed by Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-Ray Emission (PIXE) using a H+ ion beam. The knowledge of the composition of the Mg, P, Co and Ga doped ZnO films is required to understand the optical and electronic properties. Additionally, sensitive trace element analysis was carried out on some of the films in order to quantify the influence of extrinsic impurities on the magnetic properties of the samples. Furthermore, the crystalline quality and the incorporation of boron in BGaAs and BGaP thin films grown by MOVPE (V. Gottschalch, Institute of Anorganic Chemistry) were investigated using RBS/channeling as well as nuclear reaction analysis under channeling conditions. For this purpose, the proton yield from the 10B(a,p)13C nuclear reaction excited by 2.3 MeV He+ ions was recorded under channeled incidence into the {001}, {011} and {111} axis of the thin film material. The reduction of the proton yield was nearly identical with the reduction of the RBS yield from the same depth interval. From this it could be concluded that more than 90% of the incorporated Boron atoms are located on substitutional lattice sites.
Lattice distortion and atomic displacements in proton-induced freestanding GaN thin layer splitting Dipl.-Phys. Steffen Jankuhn The modification of GaN structural, electrical, and optical properties by ion implantation has attracted a great deal of attention [1]. However, in spite of more than a decade of extensive investigations, there are yet several unexplored aspects and unexplained phenomena. In particular, the influence of the implantation of hydrogen ions at intermediate fluences is still poorly understood. It was demonstrated that annealing above 500°C of hydrogen-implantedGaN (peak concentration ~12%) leads to the formation of extended internal surfaces. This phenomenon is technologically highly relevant as it could bridge the gap between cost and quality in the fabrication of GaN-based devices [2]. Our objective is to unveil the underlying physics and the atomic processes involved in hydrogen ion splitting of GaN thin layers. Due to the complexity of the microstructure produced immediately after implantation, we have employed several techniques to probe the nature of ion-induced defects and their thermal evolution leading to the splitting. Rutherford backscattering spectrometry in channeling mode (RBS/C) is the technique of choice to investigate the atomic displacements and lattice distortion. A set of GaN substrates implanted at the optimal dose of 2.6E17 cm-2 at 50 keV and annealed at different temperatures were analyzed by RBS/C using a 2 MeV He+ beam. From the RBS/C spectra, we note the presence of a damage-related peak localized at 1.25 MeV for as-implanted and annealed samples (Fig. 1).
The damage peaks for ion channeling along the {101} direction are wider than that obtained for {100}. For the annealed sample at 600°C the RBS/C spectrum indicates the existence of a shoulder which appears beyond the damage-related peak. The appearance of this shoulder coincides with the formation of nanoscopic cracks [3] and also with the positronium formation [4]. Literature: |
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