Microstructure and energy resolution of 59.6 keV /sup 241/Am gamma absorption in polycrystalline HgI/sub 2/ detectors

Abstract

Polycrystalline HgI/sub 2/ 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/sub 2/ 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 /spl mu//sub n/=87 cm/sup 2//V/spl middot/s, electron trapping time as long as /spl tau//sub n/=18 /spl mu/s, hole mobility /spl mu//sub p/=4.1 cm/sup 2//V/spl middot/s, and hole trapping time of /spl tau//sub p/=3.5 /spl mu/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 /sup 241/Am.