Gate Controlled Negative Differential Resistance and Photoconductivity Enhancement in Carbon Nanotube Addressable Intra-
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Gate Controlled Negative Differential Resistance and Photoconductivity Enhancement in Carbon Nanotube Addressable Intra-Connects Seon Woo Lee1, Slava Rotkin2, Andrei Sirenko3 ,Daniel Lopez4, Avi Kornblit4 and Haim Grebel1 , 1 Electronic Imaging Center at NJIT and the Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, NJ, 07102, U.S.A 2 Department of Physics, Lehigh University, Bethlehem, PA, 18015 3 Department of Physics, New Jersey Institute of Technology, Newark, NJ, 07102, U.S.A 4 New Jersey Nanotechnology Consortium (NJNC), Alcatel-Lucent Technologies Bell Labs, Murray Hill, NJ, 07974, U.S.A ABSTRACT Field effect transistors were fabricated using carbon nanotube (CNT) intra-connnects. The intra-connects – individual tube or a small bundle of tubes spanning across the planar electrodes – were grown by using chemical vapor deposition (CVD) precisely between very sharp metal tips on the pre-fabricated electrodes. Gate-controlled N-shaped negative differential resistance (NDR) has been demonstrated. Enhanced differential photoconductance, which was associated with NDR was observed, as well. INTRODUCTION Single-wall carbon nanotube (SWCNT) intra-connects (bridges spanning across two planar electrodes, Figure 1) have gained much interest from basic research and potential applications points of view [1-6]. Despite the key role of this relatively simple structures, only a few experimental studies have been devoted to its related negative differential resistance effect [7-10]. The lack of many experiments might be attributed to the lack of a controlled fabrication method. Here we address this issue by devising a new processing method: in some cases, more that 50% successful bridges were fabricated between pre-fabricated set of electrodes. We achieved this value by using sharp electrode tips as seed catalysts to initiate tube growth from tip to tip. All of the intra-connects fabricated in this way were SWCNT. We used this method to study the characteristics of gated structures with individual tubes or small bundles. EXPERIMENT SWCNT intra-connects were grown and self-aligned between pre-fabricated electrodes by Chemical Vapor Deposition (CVD) process [11,12]. For the present study we replaced the CO precursor gas by methane/hydrogen mixture at the elevated temperature [13]. The schematic of a field effect transistor (FET) made of individually addressed CNT intra-connect is shown in figure 1b. The silicon surface was oxidized to a thickness of 20 nm prior to the electrode deposition. The two metal electrodes were used as source and drain electrodes, respectively. The silicon substrate was used as a back gate electrode. The growth yield of such technique is quite high (ranging between 30-50%) yet, the exact reason for its success is not clear. It has been postulated in the past that the growth of a single channel is advanced by the formation of suspended graphene between the electrodes, which quickly rolls into a carbon nanotube [14].
Figure 1. (a) SEM image of the
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