Semiconductor/Insulator Interfaces in Organic Thin Film Electronics
C. Daniel Frisbie, Chemical Engineering & Materials Science, University of Minnesota, 151 Amundson Hall, 421 Washington Ave S.E., Minneapolis, MN 55455
In the last 15 years substantial progress has been made in the development of ƒà-conjugated organic semiconductors as an alternative to amorphous silicon for low cost, thin film electronics. In the late 1990s, organic semiconductors achieved sufficiently high levels of performance in thin film transistors (TFTs) that printed circuit applications could be envisioned. Better knowledge of structure-property relationships for organic semiconductor/gate insulator interfaces will be important for further advancements in OTFTs. In this talk, I will describe our observations of structural defects and correlated electrostatic potential variations at the interface between the benchmark organic semiconductor pentacene and a common insulator, silicon dioxide. Using an unconventional mode of lateral force microscopy, we have generated high contrast images of the grain boundary (GB) network in the first pentacene monolayer. Concurrent imaging by Kelvin probe force microscopy (KFM) reveals localized surface potential wells at the GBs, indicating that GBs will serve as charge carrier (hole) traps. Scanning probe microscopy and chemical etching also demonstrate that slightly thicker pentacene films have domains with high line dislocation densities. These domains produce significant changes in surface potential across the film. The correlation of structural and electrostatic complexity at organic/insulator interfaces has important implications for understanding electrical transport in OTFTs and for defining strategies to improve device performance.