A Study of Optical and Electronic Properties of a Semiconducting Polymer, Poly(o-methoxyaniline) Public Deposited

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  • March 19, 2019
  • Shrestha, Roshan Prasad
    • Affiliation: College of Arts and Sciences, Department of Chemistry
  • The optical properties of spin coated thin films of poly(o-methoxyaniline) (POMA) were investigated using spectroscopic ellipsometry (SE) complimented by optical absorption spectroscopy in the visible-near UV optical range and atomic force microscopy (AFM) for surface roughness. For these studies a custom built ellipsometer was constructed and interfaced with a computer and software was written in LABVIEW™ for automation. A Gaussian oscillator optical model was used to fit the data obtained from SE. roughness results were also evaluated in an optical model. The effect of different spin deposit conditions including spin rate, and concentration of solution and deposition ambient on the POMA film thickness, surface roughness, optical properties and optical anisotropy have been investigated. Small uniaxial anisotropy has been measured and annealing leads to some densification and surface smoothing. Organic thin film transistors (OTFT) were fabricated with POMA as the active semiconductor layer, silicon dioxide (SiO2) as the gate dielectric, heavily doped silicon as the substrate, and vacuum evaporated gold lines as the source and drain contacts. The electronic properties were characterized using a custom built probe station. The custom probe station was also automated with software program written in LabVIEW™. POMA yielded a P-channel device, and from transfer characteristic and turn-on plot, the charge mobility was calculated which was in the range of about 10-3 cm2 V-1 s-1. Various post fabrication processes were carried out to optimize the device performance. Controlled doping and moderate annealing have shown improvement in the device mobility by 10 folds and 2 folds respectively, yielding evidence for a hopping mechanism for charge transport in POMA. Two alternate gate dielectric layers for the OTFT were also considered; while a nonpolar low-K dielectric, polyethylene improved mobility; polar high-K dielectric, copolymer of vinylidene fluoride with trifluoroethylene had an adverse effect on mobility.
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  • Irene, Eugene A.
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