Small gap semiconducting organic charge-transfer interfaces

We investigated transport properties of organic heterointerfaces formed by single-crystals of two organic donor-acceptor molecules, tetramethyltetraselenafulvalene (TMTSF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Whereas the individual crystals have un-measurably high resistance, the interface exhibits a resistivity of few tens of MegaOhm with a temperature dependence characteristic of a small gap semiconductor. We analyze the transport properties based on a simple band-diagram that naturally accounts for our observations in terms of charge transfer between two crystals. Together with the recently discovered tetrathiafulvalene (TTF)-TCNQ interfaces, these results indicate that single-crystal organic heterostructures create new electronic systems with properties relevant to both fundamental and applied fields.