Berlin 2008 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 51: Poster IV

HL 51.53: Poster

Thursday, February 28, 2008, 16:30–19:00, Poster D

Study of the solubility limits and secondary phase formation for ZnO:TM (TM = V, Fe, Co, Ni) mixed crystals by Raman spectroscopy — •Martin Koerdel¹, Marcel Schumm¹, Fabian Bach¹, Huijuan Zhou², Wojciech Szuszkiewicz³, Sven Mueller⁴, Carsten Ronning⁴, and Jean Geurts¹ — ¹Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg — ²Institut für angewandte Physik, Universität Karlsruhe — ³Polish Academy of Science, Warsaw — ⁴II. Physikalisches Institut, Universität Göttingen

For ZnO alloyed with transition metal (TM) ions the possibility of room temperature ferromagnetism is predicted if the TM ions occupy cation sites. To investigate the incorporation of various TM ions (V, Fe, Co, Ni) and to check their solubility limits in the ZnO crystal lattice we study the ZnO:TM and possible TM-oxide vibrations by Raman spectroscopy. Three ZnO:TM systems are compared: (i) layers prepared by sol-gel technique from nanocrystals, (ii) ion implanted layers and (iii) bulk crystals grown (900°C) by vapor phase transport. TM ion concentration ranges up to 20 at.%. An annealing sequence (700°C, 900°C) is applied to systems (i) and (ii). Each annealing step significantly improves the crystal order. Below the solubility limit the incorporation of the TM ions only activates symmetry-forbidden ZnO host lattice phonon modes proportional to the TM ion fraction incorporated in the ZnO lattice. No TM local vibration modes are observed. TM solubility limits are typically below 10% and, moreover, depend strongly on the sample growth method. TM-oxides are identified not only by their phonons but also by magnetic excitations.