High-Density Nanosecond Charge Trapping in Thin Films of the Photoconductor ZnODEP

Science  13 Aug 1993:
Vol. 261, Issue 5123, pp. 897-899
DOI: 10.1126/science.261.5123.897


An electrooptical memory effect is observed with solid thin films of the photoconductor zinc-octakis(β-decoxyethyl) porphyrin (ZnODEP) sandwiched between two optically transparent electrodes. Upon irradiation with the simultaneous application of an electric field, electron-hole pairs are generated and separated within the photoconductive layer. These electron-hole pairs become "frozen" within the films when the irradiation is interrupted. These trapped charges can be released by irradiation of the cell, resulting in a transient short-circuit photocurrent. No cross talk between adjacent memory elements separated by ∼0.2 micrometer (a density of 3 gigabits per square centimeter) was detected. The charge storage system is robust and nonvolatile. The response time for the write-read beam is in the subnanosecond range, and no refreshing is required for long-term retention of trapped charges.