Diode-Like Properties of As-Grown Chemical Vapor Deposited Single-Walled Carbon Nanotubes

Current rectification property of as-grown single-walled carbon nanotubes (SWNTs) is investigated. The SWNTs are grown by chemical vapor deposition (CVD) process. The process allowed to grow long strands of SWNT bundles, which are then used to fabricate multiple arrays of switching devices with the channel length of 3, 5, 7 and 10 μm on a 15 mm × 15 mm SiO₂ on Si substrate. Regardless of the channel length, a majority of the fabricated devices show current rectification characteristics, with high throughput of current (I) in the forward bias (V) giving the forward and reverse current ratio (I _for/I _rev) of ∼10⁶. Atomic force microscopic (AFM) analysis of the device structure and surface topology of SWNT suggest the observed rectification of current to possibly result from (a) crosstube junctions, (b) a mixture of metallic and semiconducting tubes in the SWNT bundles, and/or (c) chirality change along a single tube. The exact mechanism underlying the observed rectification could not be conclusively established. However, the analyses of the experimental results strongly suggest the observed rectification to result from Schottky-type diode properties of SWNTs with mixed chirality along the tube.