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This work is focused on the electrical characterization of polymer field effect transistors. Conventional method of characterizing organic polymeric semiconductors includes field-effect mobility measurement and optical time-of-flight measurement of drift mobility. In this dissertation we have introduced a new method that combines the advantages of both these methods. It involves the injection of carriers at the source of a transistor using a voltage pulse followed by their subsequent extraction at the drain. The delay between the two events is used to extract the velocity of carriers. The electronic time-of-flight method is a fast, simple and direct method to determine the charge transport properties of the semiconductor. In addition it also presents itself as a source of information for understanding injection into the semiconductor and determining the trap distribution. Theoretical modeling of transport was performed. Simulation was also done to include effect of non-idealities that are forbiddingly difficult to be solved analytically. Time of flight measurements of drift mobility were performed in organic transistors with varying semiconductors and dielectrics. It was observed that the electronic time-of-flight mobility lies in the range of the field-effect mobility. Variation in drift mobility was also observed with the applied pulse voltage. This was explained to be caused due to a combination of the increase in mobility with gate voltage and the increase in drift mobility at high lateral fields. Finally mobility measurements were done on transistors with varying channel length and it was concluded that the mobility increases proportional to the exponential square root of the electric field. Finally a derivation of the pulse voltage method is discussed that involves the use of a small signal electronic impulse instead of a large signal voltage pulse. It was shown that this method could not be used to calculate the drift velocity in a polymer transistor as it is valid only for low conductivity materials whose dielectric relaxation time is lower that the transit time of the carriers injected.

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published_or_final_version / Mathematics / Master / Master of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

This thesis provides the study of graphene’s electrostatic interaction with the substrate surrounding it. Mathematical models based on current experimental configurations of graphene field-effect transistors (FET) are developed and analyzed. The conductivity and mobility of charge carriers in graphene are examined in the presence of impurities trapped in the substrate near graphene. The impurities encompass a wide range of possible structures and parameters, including different types of impurities, their distance from graphene, and the spatial correlation between them. Furthermore, we extend our models to analyze the influence of impurities on the fluctuations of the electrostatic potential and the charge carrier density in the plane of graphene. The results of our mathematical models are compared with current experimental results in the literature.

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