Variable Temperature Measurement on Operating Pentacene-Based OTFT
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1091-AA07-91
Variable Temperature Measurement on Operating Pentacene-Based OTFT Hung-Keng Chen1, Po-Tsun Liu2, Ting-Chang Chang3, and S.-L. Shy1 1 National Nano Device Laboratories, No.26, Prosperity Road 1, Science-based Industrial Park, Hsinchu, 30078, Taiwan 2 Department of Photonics and Display Institute, National Chiao Tung University, Hsinchu, 30078, Taiwan 3 Department of Physics and Institute of Electro-Optical Engineering, National Sun Yat-Sen University, Kaohsiung, 80424, Taiwan ABSTRACT Variable temperature electrical measurement is well-established and used for determining the conduction mechanism in semiconductors. There is a Meyer–Neldel relationship between the activation energy and the prefactor with a Meyer Neldel energy of 30.03 meV, which corresponds well with the isokinetic temperature of about 350 K. Therefore, the multiple trapping and release model is properly used to explain the thermally activated phenomenon. By the method, an exponential distribution of traps is assumed to be a better representation of trap states in band tail. Samples with higher temperature during measurement are observed to show better mobility, higher on-current and lower resistance, which agree well with the multiple trapping and release model proposed to explain the conduction mechanism in pentacene-based OTFTs.
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INTRODUCTION In amorphous and polycrystalline silicon, variable temperature measurements provide information about trap states and distributions in the semiconductor. They have been used to determine whether charge transport occurs in extended states, by variable range hopping (VRH), or by multiple trapping and release (MTR). The temperature and gate voltage dependence of the ) of organic-based field-effect thin-film transistors (TFTs) have been charge carrier mobility the subject of research for some years [1–8]. However, the charge transport mechanisms in these organic devices are still not fully understood. Reports vary from thermally activated behavior [2,3,6] to temperature independent transport [4]. Band-like transport in extended states was reported for high-purity single crystals of pentacene [9]. It should be noted that in contrast to this highly ordered system the carrier transport in disordered or partially ordered systems is governed by localized states, which results in a different transport mechanism. The temperature and gate in organic TFTs have been described in terms of multiple trapping [3], voltage dependence of hopping [8], and Coulomb blockade [6]. Each of these models predicts a specific temperature dependence of the charge carrier mobility that can be used to identify the underlying conduction mechanism.
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EXPERIMENT The organic TFTs were prepared by evaporated pentacence through shadow mask on a transistor test substrate in thermal coater at the temperature of 70°C. The transistor substrate consisted of silicon wafer of low resistivity as gate electrode, a 200 nm-thick SiO2 insulating layer ( Ci=17 nF/cm2 ) thermally grown in furnace and a patterned gold layer to form ohmic
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