PbI2 thick films: Growth, properties, and problems

Polycrystalline PbI2 films were grown on glass substrates with a conductive indium–tin-oxide coating using a physical vapor deposition method. Numerous dark current–voltage and current–time dependencies were recorded in order to study the electrical and detector properties of the films. A very poor correlation between the physical properties of the films and technological parameters was observed. A decrease in the distance between the crucible and the substrate lead to an increase in film density. High density (about 5 g/cm3) and good morphology films have been grown using a large crucible diameter, film growth rate of 2–4 μm/h, a heater temperature of approximately 250 °C, and a substrate-to-crucible distance of about 15–20 mm. No real correlation between the mechanical and detector properties of the films was found. This lack of correlation could be explained by a contradiction between the physical properties of the PbI2 film (polarization, long relaxation time, charge accumulation effect) and the experimental setup (irradiation of full film surface and short term measurement). The linear dependence of film sensitivity to X-ray irradiation on dark current density was observed, and a simple physical model explaining such behavior is suggested. The multi-measurement technique is also suggested as a method for obtaining the quasi-equilibrium state of films.