Optically powered ZnO nanowires with symmetric and asymmetric contacts

In this paper, we show large photovoltage and photocurrent obtained in individual ZnO nanowire devices with symmetrical and asymmetrical contacts. Ti/Au terminal electrodes were deposited for symmetrical contacts, while Ti/Au and Au electrodes were employed for asymmetrical contacts. Photovoltage and photocurrent measurements were carried out on individual ZnO nanowires devices without external bias. The symmetric nanowire devices exhibited -3 mV photovoltage and -10 nA photocurrent powered by UV laser illumination, while -60 mV photovoltage and -10 nA photocurrent were obtained for asymmetric contacts. Furthermore, the photovoltage were noticeably dependent on the local excitation position. Further calculation showed that the laser illumination reduced the Schottky barrier heights. The above results can be understood on the basis of illumination controlled Schottky barrier heights at nanowire-metal contacts and surface oxygen adsorption-desorption. We demonstrate that the simple two-terminal devices can be useful for self-powered and position sensitive photodetection, optically powered circuit, and nanowire based integrated nanophotonics.