Visible-Range Luminescence Study in Indium Oxide Nanowires
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1010-V01-05
Visible-Range Luminescence Study in Indium Oxide Nanowires Davide Calestani1, Mingzheng Zha1, Margherita Mazzera1, Laura Lazzarini1, Andrea Zappettini1, Giancarlo Salviati1, Carlo Paorici2, and Lucio Zanotti1 1 IMEM-CNR, Parco Area delle Scienze 37/A, PARMA, I-43100, Italy 2 Physics Dept., Parma University, Viale G.P.Usberti 7/A, Parma, I-43100, Italy ABSTRACT The interest in semiconducting metal oxide nanowires for gas sensing devices is today very high. Besides common materials such as SnO2 or ZnO, also In2O3 has been obtained in this quasi-1D morphology . In the present work In2O3 nanowires have been grown by vapor transport process starting from 6N pure In. For a better knowledge of the fundamental properties and the sensing mechanism of In2O3 nanowires, the obtained samples have been investigated by different techniques, focusing mainly on the optical characterization. Their morphology and structure have been studied by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray diffraction. The optical properties have been investigated as well, mainly by means of photo- (PL) and Cathodo-luminescence (CL) both applied in the UV-Visible range. A complex emission spectrum has been revealed and assigned to specific defects thanks to a deep analysis of the bands as functions of temperature (varying from 20 to 300K) and to suitable thermal treatments (in oxygen rich atmosphere at 1000∞C). Moreover, the effects of electron beam irradiation have been pointed out by performing CL spectra on a single In2O3 nanowire after different irradiation times. The possible influence of the substrate has been verified by measuring low temperature spectra on In2O3 nanowires grown both on alumina and silicon substrates.
INTRODUCTION Wide band gap semiconductor based on metal oxide offer appreciable transparency in the visible range and good infrared reflectance due to they high free carrier concentration. Thus, they are promising materials for microelectronic application [1]. Besides the well known application for heat mirrors, solar collectors, In2O3 could be employed even in microwave oven insulation, and laser or radar applications [2]. Nevertheless, by decreasing the dimensions to the nanometer scale, thanks to the favourable surface-to-volume ratio, In2O3 has been demonstrated to be an interesting material for gas sensors devices [3,4]. Optical properties of In2O3 thin films have been widely investigated, at least of our knowledge, mainly by means of room temperature photo-luminescence or optical absorption spectroscopy. They revealed In2O3 to have a direct band gap at 3.75 eV and an indirect one at 2.6 eV [5]. While the former is allowed, the latter is forbidden. In the present work, photo- and cathodo-luminescence have been applied in the temperature ranges 20-300K and 77-300K, respectively. Thanks to the careful analysis of the bands as function of temperature and to suitable treatments (as annealing in oxygen rich atmosphere or electron irradiation) some unexpected features in In2O3 emi
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