AVS 49th International Symposium
    Electronic Materials and Devices Tuesday Sessions
       Session EL+SC-TuA

Paper EL+SC-TuA8
Thermal Quenching and High Temperature Cathodoluminescent Degradation of Sulfide-Based Powder Phosphors

Tuesday, November 5, 2002, 4:20 pm, Room C-107

Session: Semiconductor Characterization
Presenter: B.L. Abrams, University of Florida
Authors: B.L. Abrams, University of Florida
L.C. Williams, University of Florida
J.-S. Bang, University of Florida
P.H. Holloway, University of Florida
Correspondent: Click to Email
Temperature effects on cathodoluminescent (CL)intensity, spectrum and degradation of ZnS:Ag,Cl powder phosphor have been investigated. Thermal quenching was studied by increasing the phosphor temperature without exposure to a continuous electron beam and measuring the decreased CL intensity. A characteristic thermal quenching temperature of 150@supero@C with an activation energy (E@suba@) of 0.87eV was observed for ZnS:Ag,Cl. Along with reduced CL intensity, the spectra shifted to longer wavelengths and changed shape at elevated temperature. The shift was dominated by band gap narrowing at high temperatures. Shape change was attributed to Cu contamination from the heater stage. The CL spectral distribution and intensity were 100% recoverable upon cooling back to room temperature when electron beam exposure was minimal (<1C/cm@super2@). With continuous electron beam exposure, CL intensity upon cooling to RT (after 24C/cm@super2@, 2keV primary beam energy) was <40% of the original intensity before heating. The loss of CL intensity at high temperatures was less than at RT for the same primary beam energy and coulombic dose. This is consistent with the Electron Stimulated Surface Chemical Reaction (ESSCR) Model of degradation which predicts that elevated temperatures will reduce the mean stay time of physisorbed gases, decreasing the rate of the surface reactions leading to CL degradation. Electron beam heating was calculated using a simple heat transfer model and was significant for powder samples. This is consistent with morphological erosion observed on the surface of the ZnS particles degraded at elevated temperatures or high power densities. It is speculated that at temperatures of about 300@supero@C, surface chemical reactions in combination with heating leads to removal of S and evaporation of Zn. Work supported by DARPA Grant MDA 972-93-1-0030 through PTCOE.