AVS 52nd International Symposium
    Thin Films Thursday Sessions
       Session TF-ThM

Paper TF-ThM3
Alternating Current Thin Film Electroluminescence (ACTFEL) from Zinc Sulfide Doped with Rare Earth Fluorides

Thursday, November 3, 2005, 9:00 am, Room 306

Session: Optical Thin Films
Presenter: D.M. DeVito, University of Florida
Authors: D.M. DeVito, University of Florida
A.A. Argun, University of Florida
M.R. Davidson, University of Florida
P.H. Holloway, University of Florida
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Thin film electroluminescent (EL) devices are an excellent source for efficient infrared emission. A wide variety of applications exist for infrared emitters, including therapeutic medical treatment, chemical analysis, infrared displays and telecommunications. Rare earth elements, such as erbium, thulium and holmium are ideal choices for dopants in phosphors because they possess a number of sharp transition in the infrared region from 850-2800nm. These rare earth dopants also emit in the visible region (400-700 nm) and have been used in a variety of visible display technologies. Zinc sulfide is a suitable semiconductor host material because it is chemically stable, possesses a bandgap of 3.6 eV at 300 K and is therefore transparent to visible and NIR photons, and provides a lattice in which electrons can be excited to ballistic energies in order to excite emission from rare earth dopants. Thin films, approximately 0.8 microns thick, of rare earth doped ZnS were RF magnetron sputter deposited at 120 W from dual targets of undoped ZnS and rare earth fluoride doped ZnS. Deposition temperature, duty cycle, sputter gas pressure and post-deposition annealing temperature were varied in a design-of-experiment to optimize the ratio of near-infrared to visible emission. Suppression of visible emission can result in energy transfer into the infrared transitions and higher NIR/visible intensity ratios. Post-deposition annealing is a key parameter for increasing this ratio, and temperatures between 350°C and 525°C for 1 hour in N@sub 2@ show good results. Maximum EL radiance for ZnS:ErF@sub 3@ at 1550 nm was increased from ~1 µW/cm@super 2@ before annealing to 28 µW/cm@super 2@ post-anneal. The optimum concentrations of both rare-earth ion and fluorine were determined by EDS and SIMS analysis.