Comparison between sublimation and evaporation as process for growing lead iodide polycrystalline films

摘要

Polycrystalline films were grown by physical vapor deposition using lead iodide purified by evaporation as starting material. Purity and stoichiometry of starting material were determined by Inductively Coupled Plasma and wet procedures. palladium film was thermal deposited as rear contact onto glass and alumina substrates 5 * 5 cm~2 in size. Onto it, lead iodide films were grown by evaporation with source temperatures from 430 to 450 °C in a 500 mmHg Argon atmosphere. Substrate temperature was from 200 to 250 °C and deposition times from 2 to 10 days. Film thickness was measured by 59.5 keV (~(241)Am) emission absorption, resulting values up to 50μm. The films were characterized by optical and atomic force microscopy, giving an average grain size up to 2μm. Film's low temperature photoluminescence confirmed the purity of the starting material. X-ray diffraction measurements of film's reflections show an intensity relation [∑I(0 0 1)]/[∑I(h k l)] from 0.2 to 0.9 that correlates to the film deposition temperature. For determining electrical and spectrometric properties, front palladium thermal deposition contacts and acrylic encapsulation were done onto the lead iodide films. Apparent resistivities from 10~(12) to 10~(15) Ω.cm and current densities in the order of 6 pA/cm~2 (50 V) were determined. X-ray film response and uniformity was checked by irradiating with an X-ray medical equipment. Film properties and performance were correlated with starting material and substrate temperature, with previous results for lead iodide films grew by other methods and with similar results for mercuric iodide films.