Charge transport in ultrathin iron-phthalocyanine thin films under high electric fields

The temperature dependent current-voltage (J-V) characteristics of 20 nm thick iron-phthalocyanine films are investigated in the temperature range of 300-30 K, and in the bias range of ±200 V. In the temperature range of 300-100 K, the charge transport is governed by bulk-limited processes with a bias dependent crossover from Ohmic (J∼V) to exponentially distributed shallow trap mediated space-charge-limited conduction (J∼V(α), α ≥ 2) to space-charge-limited conduction with field enhanced mobility (lnμ∼E(1/2)). However, at temperatures less than 100 K, the charge transport is electrode-limited, and undergoes a bias dependent transition from Schottky (lnJ∼V(1/2)) to multistep tunneling. From shallow trap mediated space-charge-limited conduction data the estimated room temperature mobility was found to be ∼1.9 cm(2) V (-1) s(-1). The high mobility of films is attributed to better structural organization due to the face-on stacking of molecules, which is supported by x-ray diffraction and UV-visible spectroscopy data.