Electrical transport across a structurally ordered phthalocyanine film: Role of defect states

We present transport measurements from 10 to 290 K on a junction made of metallic electrodes separated by a structurally ordered, 100 nm-thick metal-free H-2-phthalocyanine layer. Above 130 K, the junction is rectifying and the transport is thermally activated with a barrier of 0.148 eV. The conductance exhibits the signature of resonant tunneling across the energy levels of the molecules. Below 130 K, transport is activated with a barrier of 5.8x10(-4) eV and exhibits a zero-bias conductance anomaly at low temperature. We discuss these transport features, and the absence of magnetoresistance, in terms of the likely presence of defects due to the high structural quality of our organic spacer layer.