Microstructural and Optical Properties of Nitrogen Doped ZnO Nanowires
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Microstructural and Optical Properties of Nitrogen Doped ZnO Nanowires Ahmed Souissi1,2, Nadia Hanèche1, Corinne Sartel1, Abdel Meftah2, Alain Lusson1, Meherzi Oueslati1, Jean-Marie Bluet3, Bruno Masenelli3, Vincent Sallet1 and Pierre Galtier1 1
Groupe d’Etude de la Matière Condensée (GEMaC), Université de Versailles Saint-Quentin-en Yvelines / CNRS, 45 avenue des Etats-Unis, 78035 Versailles, France 2 Département de Physique, Université El-Manar, Tunis, Tunisie 3 Institut des Nanotechnologies de Lyon, INSA, 69621 Villeubanne, France ABSTRACT Nanowires with different nitrogen concentrations were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) using DEZn, N2O and NH3 as zinc, oxygen and nitrogen doping sources respectively. Low temperature photoluminescence, Raman spectroscopy and Transmission Electron Microscopy are combined to study the incorporation of nitrogen in the wires. The observation of donor-acceptor pair band confirms that the incorporation nitrogen in ZnO nanowires is responsible for the creation of acceptor centers. The additional peaks observed in Raman are correlated to nano-sized inter-atomic distance fluctuations observed in TEM. These domains combined with a resonance effect are probably the explanation of the huge Raman cross section observed for the impurity related peaks. INTRODUCTION The achievement of efficient and reliable p-type ZnO in bulk or thin films is still currently a serious drawback for the development of optoelectronic devices. This has been related to the presence of residual n-type impurities, the creation of structural defects during growth, the difficulty to incorporate the dopant in the adequate atomic site and/or in a shallow acceptor state or the creation of complexes favored by thermodynamics. Among all the possible candidates for p-type doping, nitrogen is a potentially interesting candidate when it is incorporated in substitution to oxygen because its size is comparable and it should not distort to much the ZnO matrix. Although a large amount of studies have reported on the incorporation of nitrogen in bulk or thin film, very few convincing results demonstrating a p-type activity have been published. One of the reasons commonly invoked to explain this is that most of the studies have been performed on Sapphire substrates which generate a lot of extended defects and/or a noticeable diffusion of Al (a very efficient n-type dopant) from the substrate to the ZnO layer. On the other hand theoretical studies predict that nitrogen leads to a deep acceptor center in substitution to oxygen [1] or is preferentially incorporated in a complicated form like, for example, molecule or interstitial complexes [2]. In this context, the realization of doped nanowires has been proposed (i) to reduce the number of extend or localized defects and (ii) to exploit surface effects in order to improve the efficiency of the dopant incorporation in electrically active sites.
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EXPERIMENTAL Nitrogen-doped ZnO nanowires have been grown on (0001) sapphire substrates in a horizontal MOCVD
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