Characterization of Carbon nanotubes Near-Infrared Photoconductive Detector

2318 | P a g e M a y 2 7 , 2 0 1 5  Characterization of Carbon nanotubes NearInfrared Photoconductive Detector Asama N.Naje, Ola A. Noori ,Mohammed A. Hamzah ,Abdulla M.Suhail 1 Physics department, Science College, Baghdad University, Baghdad,Iraq. Naje.as75@gmail.com, ,olaabdalkrem@yahoo.com, 4moh4691@gmail.com 2 Departement of optical techniques,Dijlah University College,Baghdad,Iraq. Abdulla_shl@yahoo.com *corresponding Author: Naje.as75@gmail.com ABSTRACT


INTRODUCTION
Carbon nanotubes (CNT) are one dimensional material that has been widely explored in nanoelectronic and optoelectronic due to the unique band structure excellent electrical properties.CNTs are empty cylinders made of carbon atoms.They are neither semiconductor nor metals, and are classified as semimetals.There are two different structures for nanotubes: Single Wall Carbon Nanotubes (SWCNT) and Multi Walls Carbon Nanotubes (MWCNT).MWCNTs appear as several concentric SWCNTs with different tube diameter and with different values of the chiral vectors [1,2].Recently the photoconductivity of carbon nanotubes (CNT) has attracted great interest due to possible applications of their unique optoelectronic properties for the development of novel photosensitive nanomaterials for photovoltaics photodetectors, and bolometers [3,4,5].
In the past few years, there were intensive studies on the infrared response of carbon nanotubes, the researches of photodetector of CNT show that carbon nanotubes exhibit strong infrared light absorption with broad band and fast light responses up to picoseconds, which indicated that CNTs have potential application in IR detection.Optoelectronic properties of carbon nanotubes make them very interesting component for infrared sensors [6] .
There are two types of IR detectors: photon and thermal types.In general, photon types are preferred primarily due to their superior sensitivity and resolution.Un cooled thermal sensors have attracted much attention because they operate at room temperature.These devices offer the advantage of low cost fabrication and a wide band of 8 -14 μm [7].
Optoelectronic materials that are responsive at the wavelengths in the near-infrared (NIR) region (e.g., 800-2000 nm) are highly desirable for various demanding applications such as telecommunication, thermal imaging, remote sensing, thermal photovoltaic, and solar cells [8,9] In this work, the photoconductive response of different types CNTs (SWCNT, MWCNT and functioned MWCNT) deposited on ITO glass in the NIR spectral range was obtained.

EXPERIMENTAL WORK
Indium tin oxide (ITO) with thickness 320 nm and 20 Ohm/sq was used as a substrate to deposit Aluminum electrodes, these electrodes are usually in millimeter (0.4mm) as shown in figure .1a.The substrate with electrodes is then covered with CNTs.At this step carbon nanotubes can be deposited from a solution by drop casting directly on the sample surface.
Three types of CNTs were used to prepared the solution, single wall carbon nanotubes (SWCNTs) with a diameter (1-2nm ) and length 30µm, multi wall carbon nanotubes(MWCNTs) with a diameter (10-30nm) and length (1-2µm) and functionalzation multi wall carbon nanotubes (COOH-MWCNT) with a diameter (8-15nm) and length 50 µm are dispersed in 25ml DI-methylformamide, sonicated for 2hour, and stirred for 1hour.After depositing the solution on electrodes by drop method, the samples were left to dry in room temperature.The spectral response of the samples is measured by using a laser diode with wave length 980nm and power (50mW) as the source of illumination.

RESULT AND DISCUSSION
The Hall Effect setting type (HMS3000) was used to study the electrical properties of CNTs (conductivity, carrier mobility, charge carrier concentration).Table1.the Hall measurements for different types CNTs.
The table shows that all types of CNTs are p -type semiconductor, with different carrier mobility and conductivity depending on the types of CNTs.Electrical characterization of three different types CNTs photoconductive detectors are shown in figure (2a, b, c).The CNTs dispersion between electrode is illuminated by IR laser diode (50mW).The overall increase in current was observed at room temperature.
Figure 2. Reflect a good IR photoconductive detector sensitivity, the measured gain was calculated from the ratio between the photocurrent to dark current.The measurements were carried out for F-MWCNTs, MWCNTs and SWCNTs the photoconductive gain were 258.

CONCLUSIONS
Different types CNTs photoconductive detector were fabricated on ITO glass, the device exhibiting a good response and responsivity to near -infrared (980nm) wavelength especially SWCNTs the responsivity was 0.295A/W.
Fig1a: Schematic diagram of interdigital electrodes, b: Schematic diagram of the experimental setup.