Hydrothermally Grown Single-Crystalline Zinc Oxide; Characterization and Modification
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1035-L04-01
Hydrothermally Grown Single-Crystalline Zinc Oxide; Characterization and Modification Bengt G. Svensson1, Thomas Moe Børseth1, Klaus Magnus Johansen1, Tariq Maqsood1, Ramon Schifano1, Ulrike Grossner1, Jens S. Christensen1, Lasse Vines1, Peter Klason2, Qing X. Zhao2, Magnus Willander2, Filip Tuomisto3, Wolfgang Skorupa4, Edouard V. Monakhov1, and Andrej Yu. Kuznetsov1 1 Physics/SMN, University of Oslo, Oslo, NO-0316, Norway 2 Physics, University of Gothenburg, Göteborg, SE-41296, Sweden 3 Physics, Helsinki University of Technology, Helsinki, F-02015 TKK, Finland 4 Research Center Rossendorf, Dresden, D-01314, Germany ABSTRACT An overview of our recent results on characterization and modification of high-resistivity n-type bulk zinc oxide samples, grown by hydrothermal techniques, is given. Three specific topics are addressed; (i) the role of lithium (Li) as an electrically compensating impurity, (ii) extrinsic n-type doping by hydrogen implantation, and (iii) influence of annealing conditions on deep band emission. In (i), furnace annealing of as-grown samples at temperatures above ~800 °C is shown to cause out-diffusion of residual Li impurities and concurrently, the resistivity decreases. After annealing at 1400 °C, a resistivity close to 10-1 Ωcm is obtained and the Li content is reduced from above 1017 cm-3 to the mid 1015 cm-3 range, providing evidence for the crucial role of Li as an electrically compensating impurity. For ion-implanted samples, vacancy clusters evolve during post-implant flash lamp annealing (20 ms duration) and these clusters appear to trap and deactivate Li with a resulting improvement of the n-type conductivity. However, these clusters have a limited stability and start to dissociate already after 1h at 900 °C, accompanied by a decrease in the conductivity. For topic (ii), n-type doping by hydrogen implantation is shown to enhance the conductivity by about 5 orders of magnitude already in the as-implanted state. Despite substantial loss of hydrogen, the conductivity remains stable, or even increases, after annealing up to ≥600 °C, and necessary conditions for doping by hydrogen are discussed. In (iii), the origin of the commonly observed deep band emission from monocrystalline zinc oxide is investigated using a concept of annealing as-grown samples in different atmospheres. A strong influence by the atmosphere and temperature is observed and the results can be interpreted in terms of dominant effects on the emission by vacancy-related defects. INTRODUCTION Zinc oxide (ZnO) is an old semiconductor material and the first reports date back more than 80 years[1-3], investigating crystal structure and lattice parameters by X-ray diffraction. Since the mid 1990’s, ZnO exhibits a tremendous revival and in 2006 the number of scientific articles related to ZnO was close to 3000[4], exceeding that for GaN, SiC and SiGe. A major reason for this remarkable development is the outstanding potential of ZnO as a material for ultraviolet (UV) light emitters[5]. This refers to intrinsic materia
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