A New Concept in Radiation Damage Studies: Model System for Self-Induced Radiation Damage Experiments in Thin Films

CBD was successfully applied to create a simple, controllable and cost-effective procedure for alloying PbS thin films with thorium as the first step towards establishing a system designed for the study of radiation damage in thin film semiconductors. The average concentration of thorium along the film was found to be 0.5 at%, regardless of its concentration in the deposition solution (in a 0.438-1.752 mM range). Possibly it is due to the valence difference between the lead (Pb2+) and the thorium (Th4+), thus in order to maintain charge neutrality, a lattice vacancy of Pb is likely to accompany each alloying Th ion. Therefore, large concentrations of alloying thorium in the film should be accompanied by an equal amount of lead vacancies – a situation which is likely to be above the limit of thermodynamic stability. PL measurements show a shift of ~7meV between the reference PbS bandgap and alloyed Pb(Th) bandgap, confirming the concentration of Th in the sample. PbS(Th) thin films can be applied for radiation damage studies in semiconductor thin films, by using internal radiation sources rather than the conventionally used external radiation. This can now be carried out by replacing the stable isotope 232Th (t1/2~106 years), with a radioactive isotope 228Th (t1/2~1.9 years) which is expected to provide a unique path for studying radiation damage in materials.