Study of charge carrier trapping in solution-grown alpha -HgI2 crystals by thermally stimulated currents

Abstract

alpha -HgI2 crystals grown in solution, crystals irradiated by X- or gamma -rays, crystals aged in air, crystals aged after being polarized in a high DC field, and crystals stored in an iodine atmosphere were studied by thermally stimulated currents (TSC). The general TSC spectrum of the crystals shows two peaks: at 170 and 230 K. X-ray irradiation generates deep-donor-type traps and decreases the lifetime of the charge carriers. gamma -ray irradiation introduces a large number of deep traps closely spaced in energy. By aging the crystals in air deep donor traps are introduced into a narrow layer close to the surface of the crystals. Crystals aged in air and polarized in a high DC field show a depletion of the concentration of the deep donor traps in the active zone close to the surface induced by the field. The storage of the crystals in an iodine atmosphere prevents their degradation by aging. Apparently iodine diffusion into the crystals suppresses the slight Hg-rich deviation from the stoichiometry in crystals.