Unprecedented Optoelectronic Function in Organic Conductor: Memory Effect of Photoswitching Controlled by Voltage Pulse Width

Abstract

Electrical conductivity switching is induced by photoirradiation in single crystals of α-(BEDT-TTF) 2 I 3 below 135 K. Photoirradiated crystals show differential negative resistance (DNR), and bistability is observed in the electrical conductivity as a function of applied voltage. The threshold in voltage, which induces the DNR, increases as the temperature decreases. A hysteresis loop appears in the current versus light intensity characteristic curve, and the feature of the hysteresis loop depends on the pulse width of the applied voltage. The switching to a high conductivity state is initially triggered by the laser light irradiation. The conductivity switching can be repeatedly recovered only by applying the pulsed voltages without further photoirradiation even after the current was reduced to zero, indicating a memory effect in the photoinduced conductivity switching. When pulsed voltages having smaller width and/or height than the corresponding threshold values are applied to the crystal, the field-induced recovery to the high-conductivity state due to the memory effect fades out. The thresholds in width and height of the pulsed voltage for the memory effect can be controlled by the photoirradiation light intensity. These results show that the electrical conductivity can be controlled by the width and height of the pulsed voltage as well as the light intensity without a change in temperature or pressure.