MODELING OF OPTOELECTRONIC PROCESSES IN SrS:Cu ACTFEL DISPLAY DEVICES V.P. Singh University of Kentucky, Lexington Ky A. Garcia The University of Texas at El Paso, El Paso Tx A. Aguilera Hewlett Packard, Ft. Collins Co D.C. Morton U.S. Army Research Laboratory Adelphi, Maryland

GLASS SUBSTRATE TRANSPARENT CONDUCTOR DIELECTRIC STACK PHOSPHOR DIELECTRIC STACK REFLECTIVE ELECTRODE VaVa 1µm Typical VIL for ZnS:Mn Display Device Device Structure

Insulator Phosphor Electrode Mn ) Electron ejection due to high electric field from the cathodic interface 2) Electron gains velocity, becoming “hot” 3) Electron impact excites activator atom (Mn or Cu) 4) Impacting electron reaches anode contributing to the built-in reverse field 5) Excited atom relaxes, emitting light 3 5 e-e-

SrS:Cu

Comparisons Secondary Luminance Peaks Total Luminance is Small Comparable Amount of Tunnel Current

Possible Causes for Low Luminance Lack of Tunnel Current (not the case) Excessive Impact Ionization - but this can Only Explain low Luminance but does not Explain Secondary Peaks “Other” Mechanism Needed to Explain Behavior

Hypothesize We Hypothesize a Mechanism that Causes Luminance with a Field Reduction for a Given Device History

Changing the Electric Field without Causing Tunnel Current

Current Characteristics

Luminance Characteristics

During dent ramp i L (t) 0, however there is an increase in L(t) means that electrons are recaptured by ionized activators a) Come from Interface State and only Recaptured by nearby Ionized Activators b) Formed by the Activator and a Defect Produced by the Activators Presence in the Lattice electrically forming a Dipole

Dipoles Are Activator-Bulk Trap pair Formed by the Introduction of the Activator in the Phosphor Bulk Trap is Localized in Close Vicinity of the Activator A Certain Minimum Field is Needed to Create/Maintain the dipole Positively Charged Activator Negatively Charged Trap

Transient Results Tunnel Current appears in the very first pulse Luminance becomes noticeable in the 4 th voltage pulse

Conclusions A more Complete Model is required to study SrS:Cu Currently this Dipole Model is able to Explain the Observed Features but Further work is required