<title>Trap states in electroluminescent SrS:Cu phosphor thin films using thermally stimulated luminescence</title>

Abstract

We have evaluated the trap states in SrS:Cu thin films using thermally stimulated luminescence (TSL). The TSL experimental curves were fit to a general order kinetics equation to estimate the mean trap energies, escape frequencies and order parameters. SrS films doped with Cu have been prepared on Si and AlTiO (ALO) substrates by sputtering at an elevated substrate temperature. A BaTa<SUB>2</SUB>O<SUB>6</SUB> film was then sputtered on a SrS:Cu film grown on the ALO substrate, which represents a typical thin film electroluminescence device structure. The trap states are measured as a function of the three different film structures. The three films all have a main trap state at approximately 0.4 eV, which shows small shifts for the three structures. In addition to the single TSL peak,the SrS:Cu based films have a distribution of more shallow traps. When the phosphor films are capped with BTO an additional trap state is observed at approximately 0.08eV. From the SIMS data, the BTO/SrS:Cu interface is extended after annealing, which may contribute to these additional trap states. There is large body of work on the physical processes in SrS:Cu using electrical and optical methods, which shows that the trap states play an important role in the electroluminescence from these devices.