Visible Luminescence of Rare Earth Ions Doped Amorphous Zinc Oxide Thin Films Grown by Sputtering Technique
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1035-L11-19
Visible Luminescence of Rare Earth Ions Doped Amorphous Zinc Oxide Thin Films Grown by Sputtering Technique Wojciech M Jadwisienczak1, Ajay S. Vemuru2, Saima Khan3, Aurangzeb Khan3, and Marty E. Kordesch3 1 School of EECS, Ohio University, Stocker Center 351, Athens, OH, 45701 2 School of EECS, Ohio Universtity, Athens, OH, 45701 3 Department of Physics, Ohio University, Athens, OH, 45701 ABSTRACT We report on the luminescence of rare earth (RE) (Sm, Er, Tm) ions doped ZnO films grown by the rf-magnetron sputtering technique. Samples were insitu doped with Sm ion or with Sm, Er, and Tm ions simultaneously without any intentional co-dopants and deposited on c-Si or quartz substrates at low temperatures. Selected ZnO:RE samples were thermally annealed in 200ºC1000ºC temperature range in oxygen or argon gas at ambient pressure. As-grown and annealed samples were amorphous (a-ZnO) as was confirmed by the X-ray analysis. Furthermore, aZnO:RE samples were investigated by energy diffraction, photoluminescence and cathodoluminescence. In general, CL spectra of as-grown RE-doped a-ZnO films show characteristic emission lines due to 4f-shell transitions of RE3+ ions. Optical excitation of asgrown a-ZnO doped with RE ions using above the bandgap excitation resulted in strong host emission overlapped with weak RE3+ emission bands. It was observed that a thermal annealing process promotes changes of RE ions’ environments resulting in significant 4f-shell transition luminescence intensity quenching. INTRODUCTION ZnO semiconductor is of considerable technological importance because of its potential for use in short-wavelength light emitting devices. It has interesting characteristics, such as a large direct band gap (3.37 eV), a large exciton binding energy (60 meV) and low-power threshold for optical pumping at room temperature, which are advantageous for excitonic-related device applications [1]. For many years ZnO single crystal and polycrystalline materials were considered as attractive hosts for doping with rare earth (RE) ions for optical applications [2-4]. More recently research was focused on different morphologies and luminescence of ZnO nanocomposites doped with RE ions [5-8]. However, until now, the research showed that the main obstacle of ZnO host doped with RE ions is relatively poor luminescence originating from RE ion 4f-4f transitions in contrast to that from self-activated ZnO host centers disregard of ZnO morphology. It is well known that ZnO easily forms polycrystalline phases even at room temperature and it was recently demonstrated that it can be deposited as an amorphous layer on many substrates [9]. The last one is especially advantages to use if polycristallinity or the expense of preparing large single crystals is considered. When RE ions are incorporated into amorphous semiconductor like ZnO (a-ZnO) the local environments of RE centers differ
significantly from its crystalline/polycrystalline counterparts that may result in enhancement of RE ion intra-ionic recombination. In this report w
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