Photo-conductive Detector Based on Multi-Wall Carbon Nanotubes and Conductive Polymer for Far Infrared Radiation
Assist. Prof. Dr. Wassan Rasheed Saleh/
Department of physics, College of science, University of Baghdad
Assist. Prof. Dr. Samar Younis Taha Hussein/
Department of physics, College of science for women, University of Baghdad
Marwa Abdul Rahman Dawood Hussein/Baghdad
Prof. Dr. Abdul Allah Muhsin Suhail/Dijlah University College, Department of Visual Technology
In this work, photoconductive detector working in the far infrared region at room temperature was fabricated using Multi-Wall Carbon Nanotubes (MWCNTs). The carbon nontubes suspension is deposited by dip coating technique (fabricated by us), to prepare thin films of CNTs. These films are grown on porous silicon (PSi) substrates of n-type Si. The aluminum interdigitated electrodes are evaporated on the CNTs film to fabricate the IR detectors. The fabricated detectors were illuminated by IR radiation from CO2 laser of 10.6µm wavelength and power of 1 W. The structural, morphological, optical properties and Hall measurements of the film were studied. The structure of the MWCNTs film is examined by X-ray diffraction (XRD) and found to be polycrystalline of hexagonal structure with strong orientation at (002). The Atomic Force Microscope (AFM) studies are focused on the characterization of the PSi-CNTs and found it had a good and uniform surface homogeneity which gives a good indicator for formation of the MWCNTs over the nanospikes of Si, while the scanning electron microscope (SEM) technique shows that the film are homogeneous and do not have areas with clusters or cracks. FTIR spectrophotometer was used to study the infrared spectrum of CNTs, and revels that CNTs have good absorbance around wavelength of 10 mm (1000 cm-1). This is mean that these materials are very good candidate for IR applications. Hall Effect measurements show that the carbon nanotubes deposited on porous silicon substrate has a p-type semiconductor behavior and high conductivity in about 5.104×10+3(W.cm)-1. The I-V characteristics of the detector were measured at forward bias voltage (0.5-5) volt, after connected the detector to the electric circuit. The figure of mertis (responsivity Rl, photo gain G, quantum efficiency QE, noise equivalent power NEP, and specific detectivity D*) were calculated. The photoresponse enhancement of the photoconductive detector is improved by coating (functionalized) the CNTs films with layer of 100 mm of the blend polyaniline (PANI), polymethylmeth acrylate (PMMA) and methylene blue (MB) dye. These types of polymers coating can be considered as a surface treatment of the detector film, which highly increases the photoresponse and specific detectivity of the fabricated CNTs IR detector. The figure of merits was calculated before and after coating process. It is found that the responsivity increased from 0.0052 A/W to be 0.0095 A/W and the specific detectivity increased from order of 10+7(cm.Hz1/2)/W to become in order of 10+11 (cm.Hz1/2)/W after coated with polymer, while the gain for the coated samples is increased in about 25 time than that for uncoated samples. The response time for the fabricated MWCNTs IR photoconductive detector was about 23 ms and reduced to 1.5 ms after functionalized with blend of polymers and MB dye. This consider an acceptable time for this type of detectors. These values give improve for the effect of polymer on the enhancement of the performance of far IR photoconductive detector.