Spectral-resolved microprobe cathodoluminescence investigations of Al-doped single-crystalline Ba_(0.6)Sr_(0.4)TiO_3 thin films

摘要

Single-crystalline Al-doped Ba_(0.6)Sr_(0.4)TiO_3 (BST) thin films have been pulsed-laser deposited onto Ir/MgO buffered Si substrates. Spectral-resolved microprobe cathodoluminescence measurements of Al-doped BST thin films at room temperature clearly showed three detectable luminescence bands in the wavelength range between 200 and 900 nm. We assigned the first shoulder peak to saturation of phonon-assisted processes, with a band gap transition resulting in the second sharp band. The band-maximum position of a third (defect-related) broad luminescence band varied with varying the concentration of Al dopant. By fitting this latter band as the sum of three superimposed Gaussian curves, it was revealed that the incorporation of Al dopant into the BST crystal lattice had a direct impact on the defect population existing in the single-crystalline film. For perovskite ABO_3-structured BST thin films, it is suggested that the Al dopant occupies the B site (Ti) in a low range of dopant concentrations, while at higher dopant concentrations Al might occupy both A sites (Ba or Sr) and B sites.