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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  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 μn=87 cm2/V·s, electron trapping time as long as τn=18 μs, hole mobility μp=4.1 cm2/V·s, and hole trapping time of τp=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.