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Title: Energy dissipation channels affecting photoluminescence from resonantly excited Er{sup 3+} ions doped in epitaxial ZnO host films

We identified prerequisite conditions to obtain intense photoluminescence at 1.54 μm from Er{sup 3+} ions doped in ZnO host crystals. The epitaxial ZnO:Er films were grown on sapphire C-plane substrates by sputtering, and Er{sup 3+} ions were resonantly excited at a wavelength of 532 nm between energy levels of {sup 4}I{sub 15/2} and {sup 2}H{sub 11/2}. There is a threshold deposition temperature between 500 and 550 °C, above which epitaxial ZnO films become free of miss-oriented domains. In this case, Er{sup 3+} ions are outside ZnO crystallites, having the same c-axis lattice parameters as those of undoped ZnO crystals. The improved crystallinity was correlated with enhanced emissions peaking at 1538 nm. Further elevating the deposition temperature up to 650 °C generated cracks in ZnO crystals to relax the lattice mismatch strains, and the emission intensities from cracked regions were three times as large as those from smooth regions. These results can be consistently explained if we assume that emission-active Er{sup 3+} ions are those existing at grain boundaries and bonded to single-crystalline ZnO crystallites. In contrast, ZnO:Er films deposited on a ZnO buffer layer exhibited very weak emissions because of their degraded crystallinity when most Er{sup 3+} ions were accommodated into ZnO crystals. Optimizing themore » degree of oxidization of ZnO crystals is another important factor because reduced films suffer from non-radiative decay of excited states. The optimum Er content to obtain intense emissions was between 2 and 4 at. %. When 4 at. % was exceeded, the emission intensity was severely attenuated because of concentration quenching as well as the degradation in crystallinity. Precipitation of Er{sub 2}O{sub 3} crystals was clearly observed at 22 at. % for films deposited above 650 °C. Minimizing the number of defects and impurities in ZnO crystals prevents energy dissipation, thus exclusively utilizing the excitation energy to emissions from Er{sup 3+} ions.« less
Authors:
 [1] ;  [2]
  1. NTT Device Innovation Center, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198 (Japan)
  2. Kurume National College of Technology, 1-1-1 Komorino, Kurume, Fukuoka 830-8555 (Japan)
Publication Date:
OSTI Identifier:
22402889
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 15; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CONCENTRATION RATIO; CRACKS; CRYSTAL DEFECTS; DEPOSITION; DOPED MATERIALS; ENERGY LOSSES; EPITAXY; ERBIUM IONS; ERBIUM OXIDES; EXCITATION; EXCITED STATES; GRAIN BOUNDARIES; LATTICE PARAMETERS; MONOCRYSTALS; PHOTOLUMINESCENCE; PRECIPITATION; SAPPHIRE; THIN FILMS; ZINC OXIDES