Microstructure and energy resolution of 59.6 keV 241Am gamma absorption in polycrystalline HgI2 detectors

Polycrystalline HgI₂ layers prepared by different modifications of physical vapor deposition (PVD) exhibit different microstructure. Under some fabrication procedures, the samples exhibit a columnar structure, with columns highly oriented in the [001] direction (c-axis) normal to the layer surface. Differences in manufacturing procedures manifest themselves in different average column length, different porosity, and different average material density. The most nonporous, dense, thick HgI₂ layers are obtained by activating the preferential growth along the c-axis perpendicularly to the substrate plane. The microstructure correlates to the material electrical conduction properties: dark current, mobility, and trapping time. For a sufficiently pure starting material, and grain length approaching the layer thickness, the layer may exhibit electron mobility as high as μ_n=87 cm²/V·s, electron trapping time as long as τ_n=18 μs, hole mobility μ_p=4.1 cm²/V·s, and hole trapping time of τ_p=3.5 μs. These values are quite close to those of a single crystal. Nuclear detectors fabricated using such layers exhibit energy resolution of gamma absorption, as demonstrated for the 59.6 keV emission of ²⁴¹Am.