Polycrystalline mercuric iodide films: Deposition, properties, and detector performance

We report the room temperature α-particle response of a detector fabricated from high purity polycrystalline mercuric iodide thin films. The films are deposited by physical vapor deposition technique using multi-passed zone refined high purity starting material. The films of ∼15 μm thick were deposited on indium-tin-oxide (ITO) coated glass substrate and were shown to be reasonably compact and have uniform surface morphology by cross-sectional SEM study. Photoluminescence at 10 K showed two distinct peaks at 533 nm and around 560 nm. A previously reported peak at ∼620 nm mainly attributed to the presence of impurities was not present. The room temperature α-particle response measurements were carried out under vacuum and demonstrated that charge collection efficiency can be obtained with thin polycrystalline HgI₂. We have demonstrated that a full energy peak is developed, although first indications are that the performance is significantly poorer than a silicon charged particle detector. The charge collection was found to improve with voltage, as expected.