Electron beam tuning of carrier concentrations in oxide nanowires

Abstract

In spite of the attractive electrical properties of metal oxide nanowires, it is difficult to tune their surface states, notably the ionic adsorbents and oxygen vacancies, both of which can cause instability, degradation, and the irreproducibility or unrepeatable changes of the electrical characteristics. In order to control the surface states of the nanowires, electron beams were locally irradiated onto the channels of metal oxide nanowire field effect transistors. This high energy electron beam irradiation changed the electrical properties of the individual metal oxide nanowires, due to the removal of the negative adsorbents (O2-, O-). The detachment of the ionic adsorbents changes the charge states of the nanowires, resulting in the enhancement of the electrical conductance in n-type nanowires (ZnO, SnO2) and the degradation of the conductance in p-type nanowires (CuO). By investigating the changes in the electrical properties of nanowire devices in air or vacuum, with or without exposure to electron beams, the roles of the physisorbed water molecules or chemisorbed oxygen molecules can be independently understood. Unlike the electron beam irradiation, the vacuum enhanced the conductance of both n-type (ZnO, SnO2) and p-type (CuO) nanowires, due to the release of charges caused by the detachment of the polarized water molecules that were screening them from the surface of the nanowires, irrespective of the major carrier type. The electron beam irradiation technique has the potential to locally modulate the charge carriers in electronic nanowire devices, and the changes could be maintained with proper passivation for the long-term preservation of the device characteristics.