Studies of light effects on electrical properties of ambipolar organic field - effect transistors

• Main Authors: Dian-YiWu, 吳典逸
• Other Authors: Horng-Long Cheng
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/93296355445113973816

碩士 === 國立成功大學 === 光電科學與工程學系 === 101 === This study investigated the effects of light irradiation on the electrical characteristics of pentacene-based organic thin-film transistors (OTFTs). The study can be divided into two parts. The first one focuses on the influence of light irradiation on the ambipolar electrical characteristics of pentacene-based OTFTs. The second one focuses on the effects of light irradiation on the electrical characteristics of unipolar and ambipolar pentacene-based OTFTs with the same gate dielectric buffer. 　　In part 1, we studied the light effects on the ambipolar characteristics of pentacene-based OTFTs with poly(methyl methacrylate) (PMMA) as a buffer gate dielectric layer. During light irradiation, we observed increased output drain current and higher charge mobility of devices for both p- and n-channel operations compared with those without light irradiation. Meanwhile, light irradiation also resulted in increased subthreshold swings and shifted threshold voltage. These results were attributed to excitons formed upon light absorption of the pentacene active layer that dissociated into free carriers and thus contributed to the output current. An early threshold voltage of the devices was observed for p-channel operations. By contrast, a delay threshold voltage was observed for n-channel operations. For both operations, we observed that light irradiation weakened the ability of gate modulation on the channel current. Impedance–admittance analysis results revealed that light irradiation on devices did not increase the interfacial trap density within the active channel. Finally, we concluded that variations in the electrical characteristics of pentacene-based ambipolar OTFTs upon light irradiation were due to the dual effects of light and electric fields. In part 2, we studied and compared the effects of light irradiation on the electrical characteristics of unipolar p-channel OTFTs and ambipolar OTFTs. Unipolar p-channel and ambipolar OTFTs with a pentacene active layer were prepared using PMMA buffer gate dielectric layers fabricated under different conditions. During light irradiation, increased output drain current, higher charge mobility, and larger subthreshold swing were observed for both devices. However, the light-induced threshold voltage shift in the unipolar devices was two times larger than that of the ambipolar devices. The resulting large shift in the threshold voltage of the unipolar devices was attributed to the less electron–hole recombination in the active channel. Consequently, free carriers from light irradiation directly contributed to the output current. Therefore, the unipolar devices had the potential to be a light sensor.