Microstructure and Energy Resolution of 59.6 keV Am Gamma Absorption in Polycrystalline HgI Detectors

Polycrystalline HgI 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 HgI layers are obtained by activating the preferential growth along the c-axis perpendicularly to the substrate plane. The microstruc- ture 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 cm /V s, electron trapping time as long as s, hole mobility cm /V s, and hole trapping time of s. 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 Am.