Opto-Electronic Properties of Mercuric Iodide

The optical and photoelectrical properties of mercuric iodide crystals and layers have been investigated, particularly as affected by the phase transformation from tetragonal (low-temperature form) to ortho-rhombic (high-temperature form) which occurs at 400°K. The largest temperature coefficient for band-gap variation of any known material is found for the orthorhombic form: -24×${10}^{-4\mathrm{}}$ ev/degree. The following phenomena are discussed: (1) location and temperature dependence of absorption edge by measurements of transmission, reflectivity, and photoconductivity response spectra; (2) temperature dependence of dark current; (3) electrode effects in photoconductivity; (4) variation of dark current and photocurrent through the phase transformation; (5) thermally-stimulated-currents; (6) variation of photocurrent with voltage, light intensity, and temperature. Temperature-quenching of photoconductivity in Hg${\mathrm{I}}_2$ crystals can be described by means of the same analysis as has been applied to various $A^{\mathrm{II}}{B}^{\mathrm{VI}}$ photoconductors, giving a location of 0.5 ev above the valence band for the "sensitizing" centers in Hg${\mathrm{I}}_2$.