Photo- and Thermal Annealing-Induced Processes in Carbon Nanotube Transistors
- PDF / 211,809 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 79 Downloads / 219 Views
N16.2.1
Photo- and Thermal Annealing-Induced Processes in Carbon Nanotube Transistors Moonsub Shim, Giles P. Siddons, Jae Kyeong Jeong, and David Merchin Department of Materials Science and Engineering, University of Illinois at UrbanaChampaign, 1304 W. Green St. Urbana, IL 61801
ABSTRACT Photoinduced conductivity changes and effects of thermal annealing in carbon nanotube transistors have been examined. Low-intensity ultraviolet light significantly reduces the p-channel conductance while simultaneously increasing the n-channel conductance. A combination of optical absorption and electron transport measurements reveals that these changes occur without variations in dopant concentrations. Measurements with different metals reveal that UV induces oxygen desorption from the electrodes rather than from nanotubes. In Ti-nanotube contact where the Schottky barrier plays an important role, photodesorption of oxygen mainly occurs from the native oxide of Ti electrodes. Decrease in the p-channel conductance arises from the metal work function change which causes larger hole Schottky barrier. Non-Schottky Pd-contacted nanotube transistors do not show photodesorption effects with low intensity UV. Thermal annealing of nanotube transistors with Ti/Au electrodes also leads to the disappearance of the photodesorption effects. However, a noticeable p-doping is observed to upon air exposure after thermal annealing.
INTRODUCTION Single-walled carbon nanotubes (SWNTs)1 with diameter and chirality dependent electronic structure have provided a unique system to study 1-D electron transport properties.2 A variety of potential applications ranging from computer logic circuits3 to chemical sensors4 has also been demonstrated. With an increasing interest in their optical properties,5 a combination of their unique electrical conductivity with optical effects should open up new opportunities. However, relatively little is known about how light affects the transport properties of SWNTs. A striking decrease in the electrical conductance of SWNT field-effect transistors (FETs) has recently been observed and has been attributed to oxygen photodesorption.6, 7 The extreme sensitivity of electrical conductivity of nanotubes to oxygen is an important and currently debated issue. 8,9,10 One of the limiting consequences of oxygen adsorption has been the suppression of n-channel conduction. Initially, p-doping has been suggested to occur due to oxygen adsorption on nanotubes.8,10 More recently, Schottky barriers at the metal-nanotube contacts have been shown to determine many transport properties of SWNT FETs11,12 and the apparent p-type-only observation has been attributed to work function changes brought on by oxygen adsorption on metal electrodes resulting in asymmetric Schottky barriers rather than doping effects.9 Understanding how photoinduced desorption of oxygen alters nanotube transistor characteristics will provide new insights into the role of oxygen on the observed properties of carbon nanotubes and
N16.2.2
will be required for any po
Data Loading...
