Material characterisation of SrS:Ce,Mn,Cl films

Various thin film material characterisation methods are employed to analyse evaporated SrS:Ce,Mn,Cl EL phosphors. Besides the standard techniques like XRD and SEM for crystallinity and morphology inspection the doping and codoping properties are determined by RBS, EPR and SIMS investigations. In particular, the correlation between EPR and RBS data is suited for the evaluation of the Ce doping process. At the optimum Ce-doping concentration for EL operation of 0.1 mol.%, the Ce atoms are entirely incorporated as Ce3+ ions at Sr lattice sites in the SrS host. Introducing codopants like Mn cations the optimum Ce concentration could be increased. However, the incorporation of codopants is accompanied by the formation of local distortions of the octahedral vicinity of Ce3+ indicated by a shift of the g-value in the EPR signals. The stoichiometry as well as the Cl concentration are evaluated using the RBS and SIMS techniques. The Cl incorporation, which cannot be avoided if CeCl3 is taken as a precursor, is shown to depend on the substrate temperature.