Conduction mechanisms in ZnO nanowires based Schottky diode grown under an electric field

Abstract

We present a cathodoluminescence (CL) and electrical study of aligned ZnO nanowires based Schottky diodes synthesized by applying an AC electric field between two Au microcontacts. Our results reveal that the applied electric field aligns the ZnO nanowires between the electrodes and inhibits the formation of ZnO oxygen vacancies (VO). Local CL measurements of ZnO nanowires grown at different zones of the device show that the applied electric field inhibited the formation of oxygen vacancies (VO). Furthermore, CL spectra display an energy shift of the ZnO band edge emission, generated by changes in the relative intensity of two CL bands centered at 3.23 and 3.27 eV that correspond to the donor-acceptor pair and free electrons-acceptor transitions, respectively. We propose the formation of zinc vacancies (VZn) in nanowires that act as acceptor centers in the generation of these two electronic transitions. I-V curves acquired at room temperature reveal the photoresponse of the ZnO nanowires based Schottky diode exposed under UV (365 nm) illumination, exhibiting photocurrent intensities several times higher than that observed under dark conditions for applied bias lower than 1 V. The electrical conduction mechanisms in aligned ZnO nanowires of the device were tunneling and thermionic-emission for applied bias lower than 400 and 700 mV under dark and UV (365 nm) illumination conditions, respectively. For higher bias values, the device showed a conduction mechanism type field-emission.