Photoelectrical effect and current-voltage characteristics in DNA-metal Schottky barriers

We report the first observation of unanticipated photoelectric effects (PE) under visible and near-infrared illuminations and diode-type rectifying current-voltage (I-V) characteristics in DNA-metal contact devices. These devices are constructed with DNA film sandwiched between gold (or some other metal) and transparent conductive ITO electrodes. Since the gold work function and the bangaps of ITO and DNA are greater than 4 eV, in order to release an electron in these materials, the photon energy must be greater than 4 eV, indicating an ultraviolet light source is needed. To explain these phenomena, we hypothesize that a Schottky barrier was formed at DNA-gold interfaces when the gold layer was deposited on the soft DNA film during the sputtering process. The Schottky barrier could replace the gold work function in the DNA-gold interface and greatly reduce the potential barriers. The lowered Schottky potential barrier allowed the electrons, excited by lower photon energies, to overcome the barrier into the conduction band and generate photocurrent. The observed photoelectrical effect was used to measure a similar to 1.52eV Schottky barrier height in DNA-gold contacts. Furthermore, we measured static I-V characteristics of the DNA-metal devices showing typical diode-rectifying behaviors. The observed photoelectrical effect and I-V characteristics strongly suggest a Schottky barrier at the DNAmetal interface.