Publication Date

2014-07-28

Availability

Open access

Embargo Period

2014-07-28

Degree Name

Master of Science (MS)

Department

Electrical and Computer Engineering (Engineering)

Date of Defense

2014-07-03

First Committee Member

Sung Jin Kim

Second Committee Member

Michael Wang

Third Committee Member

Weizhao Zhao

Abstract

Organic field effect transistors (OFETs) have several advantages over the conventional inorganic field effect transistor such as easy fabrication process, low-cost mass production capability and low temperature process that enables flexible substrate based device. Many applications using polymer based transistor devices are demonstrated. Successful demonstrations of Logic-gate operation, visible-IR detection and various sensor operations and the advantages discussed above show its great potential as a next generation device technology and attract many researchers to delve to improve the device properties. However, there are several disadvantages on the organic materials such as short lifetime, disability to operate under severe conditions and low carrier mobility. Among those the low carrier mobility is a critical hurdle to develop high performance device operation. Its low mobility limits the operation speed of the device, efficient amplification and carrier transport in a detector device. In this thesis, hybrid organic transistors using Poly(3-hexylthiophene-2,5-diyl)(P3HT) and metal nanostructure are introduced. The metal nanostructure has a unique localized surface plasmon resonance property that can be tailored by adjusting the shape and size of the metal structures. Therefore, the hybridization using polymer semiconducting materials and metal nanoparticles can provide plasmon based optical response and improved mobility due to the free electron concentration in the metal nanostructure. We fabricated organic thin film transistor on a highly doped silicon substrate and characterized its electrical properties as a transistor operation and optical detection properties as a field effect transistor based detector. Then, metal nanoparticles have been deposited by vacuum evaporation of small molecules on the surface of the OFETs. The electrical and optical properties have been investigated to compare with a device without plasmonic nanostructure. We successfully demonstrated the improved optical properties of the OFETs are due to surface plasmon resonance of the metal nanoparticles. The metal nanoparticles incorporated in organic transistor shows improved drain current due to the increased conductivity assisted by the free electrons in the metal nanoparticles. In addition, we observed enhanced photo responsivity (A/W) in its optical detector operation. A slight change of the spectral response was observed and we believe that this is originated from the contribution of the plasmon induced hot electrons in the metal nanoparticles. Further studies to have better understandings on metal nanoparticle incorporated in organic transistor were discussed in this thesis.

Keywords

organic field effect transistor; hybrid organic transistor; metal nanoparticle; metal nanostructure; localized surface plasmon resonance; enhanced optical and electrical properties

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