Low Temperature Aqueous Polymeric Precursor Processing of ZnO:Er Using a Glycerol Chelating Agent
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Low Temperature Aqueous Polymeric Precursor Processing of ZnO:Er Using a Glycerol Chelating Agent Uma Choppali and Brian P. Gorman Department of Materials Science and Engineering, University of North Texas, PO Box 305310, Denton, TX, 76203
ABSTRACT Erbium doped ZnO (ZnO:Er) is considered to be a suitable candidate for fabrication of the current injection optical devices. Although ZnO: Er thin films have been synthesized previously by pulsed laser deposition, we present low – temperature processed ZnO:Er thin films from polymeric precursors. In this work, we study the effect of variation of Er doping concentration on the structural and electrical properties of the synthesized films. ZnO nanoparticles of varied Er doping concentration, derived from the prepared polymeric solution, has been spin – coated onto surface modified substrates, and annealed at different temperatures. The effect of Er doping concentration on film grain size and strain was analyzed using X-ray diffraction. XRD data reveals that doping of Er ions reduces compressive strain considerably in the films. It is speculated that the presence of larger Er cations in ZnO cause tensile stress, which neutralizes the inherent compressive stress, observed in undoped ZnO, significantly decreasing and hence, making the films stress free. Crystallite size of ZnO:Er thin films, annealed at 600οC, was calculated to be approximately 12 nm using Scherrer’s equation. The surface morphology of the thin films was characterized by both SEM and AFM. Electrical resistivity of the films, annealed at 450°C, was calculated to be 290 Ω-m for 5 at wt% and 125 Ω-m for 10 at wt% ZnO:Er films. INTRODUCTION Erbium doped semiconductors have gain attention due to their niche applications in optoelectronics. These semiconductors exhibit sharp photoluminescence at 1.54 µm, making them suitable for planar optical waveguides [1, 2] and single crystal fibers [3]. ZnO has been proposed as a host semiconductor for Er cations [4]. ZnO has a direct wide band gap of 3.24 eV and a large excitonic binding energy of 60 meV at room temperature. To date, ZnO:Er films have been synthesized by pulsed laser deposition [4, 5, 7], thermal evaporation [6], and chemical solution routes [1, 2, 8]. In [1], a suspension of zinc acetate dehydrate in acetanhydride was heat treated to synthesize ZnO precursor for its condensation. Erbium acetate was later added to this ZnO colloidal sol to dope it with Er cations. In [8], prepared ZnO sols were doped with Er ions by adding erbium acetate in presence of different silanes. Er – doped nanocolloids were prepared by addition of methanolic tetramethylammonium hydroxide, zinc acetate dehydrate and erbium acetate powder [2]. Although high quality ZnO:Er thin films were prepared, these processing routes utilize expensive chemicals, are time – consuming and complicated.
In this paper, we employ simple aqueous polymeric precursor process to synthesize ZnO:Er thin films. The prepared polymeric precursors, with different at wt% Er, were spincoated on substr
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