Molecular Dipole-Modulated Charge Transport across Organic Monolayer-Modified Metal–Semiconductor Junctions

Abstract

The effect of molecular dipoles on charge transport across organic monolayer-modified metal–semiconductor junctions has been investigated systematically. We have prepared a new set of organic monolayers with varied terminal derivatization on crystalline silicon to construct molecular junctions using mercury drops as the top contact electrode. Although the surface and structural characterization indicated the high quality and uniformity of all these monolayers, the junctions (Hg/R–Si≡) showed a diverse electrical performance. Beyond taking the most common theoretical approach to analyze these molecular junctions, that is, applying the thermionic emission model (TE) to calculate the barrier height (ΦB) and ideality factor (η), we have examined the contribution of the carrier generation–recombination (CGR) mechanism by fitting the experimental current–voltage curves. When η is close to unity, the charge transport across these molecular junctions is dominated by TE; for η values greater than unity, TE indeed remains the dominant current transport pathway, while CGR transport becomes significant.