Mobility of sodium in SrS based thin film electroluminescent structures grown by atomic layer epitaxy

Abstract

Mobility of sodium in SrS-based electroluminescent thin film stacks grown by atomic layer epitaxy was studied in the temperature range 600–850 °C using ion implantation for doping and nuclear resonance broadening for profiling of sodium. The crystallinity and orientation of SrS and SrS:Ce films were studied using wide angle x-ray scattering (WAXS). It was found that sodium diffuses rapidly to the interfaces between SrS and upper and lower Al2O3 insulators. These insulators act effectively as diffusion barriers for sodium up to a temperature of about 700 °C. In the case of SrS:Ce films, even after annealing at high temperatures for long times, the Na concentration in the bulk of the film remained in the range 0.4–0.6 at. % which is about two to three times the concentration of Ce. WAXS measurements revealed the preferred [111] orientation of SrS and SrS:Ce films with an average size of crystallites ⩾120 nm. It turned out that annealing for a few hours at about 700–750 °C was needed to recover the implantation damage and restore the crystallinity of SrS to its original level.