Electro-optical characterization of in-plane grown carbon nanotubes

We have fabricated field-effect transistor (FET) structures using arrays of carbon nanotubes (CNTs) as the conducting channel by using chemical vapor deposition to achieve in-plane growth from nanometer-scale Ni dot patterns on the Au/Cr metal electrode pairs as catalyst tips. Detailed studies of the transfer characteristics of the CNT-FETs have been carried out as a function of the number of CNTs bridging the contact gap. Both, ambipolar and unipolar FET behaviors have been observed at room temperature. Devices containing 12 (6) CNTs bridging the gap display CNT-FET on/off ratios of 2 (4), respectively. Best results have been achieved for devices containing 3 semiconducting CNTs displaying pronounced on/off ratios up to 370 at room temperature. In addition, a correlation between source-drain current and optical illumination has been observed, indicating a photoeffect of the CNT arrays. The measured photocurrent depends linearly on the source-drain voltage indicating that the generated electron-hole pairs are effectively separated by the applied bias, making such devices of interest for photovoltaic applications. The demonstrated access to individual CNTs with pronounced semiconducting behavior opens the possibility to form more advanced nanoelectronic structures such as CNT quantum dots with the ultimate goal to realize single electron memory elements operating at room temperature.