Charge storage in ZnIn2S4 single crystals

We observe that, when ZnIn2S4 monocrystals at a temperature below 170°K are illuminated by light of the gap energy, the dark resistance, after illumination, is lowered by about nine orders of magnitude. This high-conductivity state persists until the crystals are either (a) warmed to room temperature, (b) exposed to light of a definite energy less than the gap width, or (c) placed in an electric field. We propose a level 1.76 eV above the valence band, with a repulsive barrier of 0.11 eV, which an electron must penetrate to enter this level and recombine.