CONDUCTION PROPERTIES OF METAL-ORGANIC MONOLAYER SEMICONDUCTOR HETEROSTRUCTURES

We have fabricated and characterized rectifying devices made of metal/ organic monolayer/semiconductor heterostructures. The devices consist of an organic barrier layer sandwiched between an aluminum (Al) metal contact and a p-type Si semiconductor. The barrier materials were chos en from three types of self-assembled monolayers (SAMs) with different electronic properties: (1) wide-band gap poly(diallydimethyl ammonium ) chloride (PDDA) 2, narrow-band gap PDDA/NiPc (nickel phthalocyanine tetrasulfonate), and donor type PDDA/PPP (poly p-quaterphenylene-disul fonic-dicarboxylic acid). From current-voltage (I - V) measurements at room temperature, we have found the turn-on voltage of the devices ca n be tuned by varying the structure, hence electronic properties, of t he organic monolayers, and that there exists a power-law dependence of I on V, I proportional to V-alpha, with the exponent alpha = 2.2 for PDDA, 2.7 for PDDA/NiPc, and 1.44 for PDDA/PPP as the barrier layer, r espectively. Our results imply that the transport properties are contr olled by both the electronic properties of the SAMs and those of the m etal and semiconductor, as indicated by the power-law dependence of th e I - V characteristics. (C) 1998 American Institute of Physics. [S000 3-6951(98)03744-9]