Optoelectronic properties of some red mercuric iodide (α-HgI2)
crystals have been studied for wavelengths 450-700 nm at temperatures 80-300 K.
These crystals were grown (a) by solvent evaporation from α-HgI2-tetrahydrofurane
saturated solution, (b) by hydration of α-HgI2-dimethyl
sulphoxide-methanol saturated solution and (c) by polymer controlled growth
(PCG) in vapour phase. Important aspects of optical generation of the charge
carriers have been discussed. The measurements of thermally stimulated currents
were also carried out in order to understand the temperature dependence of
photocurrents in different wavelength regions. With the computer simulation of
the photocurrent versus wavelength spectrum, the room temperature transport
properties (the mobility-lifetime products and surface recombination velocities
of the two charge carriers) for the crystals of three types have been
estimated. For a typical electric field strength of about 2103 V/cm, the electron drift
lengths for the crystals of three types were found to be 1150, 1350 and 6500 m,
respectively, whereas the hole drift lengths were found to be 50, 50 and 150 m,
respectively. As the typical thickness of α-HgI2
photodetector for any scintillation spectrometer is about 300 m,
under the negative electrode illumination, all the three types of α-HgI2
crystals present high potential for their use as photodetectors in conjunction
with most of the scintillators.
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