Effect of light irradiation on the characteristics of organic field-effect transistors

Abstract

Highly sensitive thin-film organic phototransistors: Effect of wavelength of light source on device performance J. Appl. Phys. 98, 074505 (2005); 10.1063/1.2061892High-photosensitivity p -channel organic phototransistors based on a biphenyl end-capped fused bithiophene oligomer Appl. Phys. Lett. 86, 043501 (2005);The effect of light irradiation on the characteristics of organic field-effect transistors containing sexithiophene ͑6-T͒ and pentacene was examined. Organic phototransistors ͑OPTs͒ in which 6-T and pentacene were incorporated were fabricated. Their response behaviors were investigated under conditions of irradiation by either modulated or continuous ultraviolet light with various intensities. Both devices showed two distinguishable responses, i.e., fast and slow responses from photoconductive and photovoltaic effects, respectively. The fast response is mainly the result of the generation of mobile carriers by the absorption of a photon energy higher than the band gap energy of the semiconductor and, subsequently, an increase in conductance via a greater flow of photogenerated mobile carriers into the channel layer. On the other hand, the slow response, which was confirmed by a light induced shift in the threshold voltage ͑V th ͒ or the switch-on voltage ͑V O ͒, is the result of a slow release of accumulated and trapped electrons in the semiconductor-gate dielectric interface. The V O is defined as the flatband voltage of devices. Below the V O , the channel current with the gate voltage is off current, and the channel current increases with the gate voltage above the V O . The speed of release of the accumulated charge was dependent on the type of semiconductor used. Pentacene OPTs showed a particularly long retention time. Even after storage for ten days, the shifted V O ͑or V th ͒ for the pentacene OPTs by light irradiation was not restored to the original value of the fresh devices. We conclude that this long sustained V th shift renders them attractive for use in "light-addressable nonvolatile memory devices."

High Photoresponsivity of Pentacene-Based Organic Thin-Film Transistors with UV-Treated PMMA Dielectrics

“…Photoresponsivity ͑R ph ͒ is estimated using R ph = I ph /͑E·W·L͒, where I ph is the photoinduced excess drain current and E is incident light intensity ͑W/cm 2 ͒. 8 When the gate bias increases, R ph is enlarged. This is known as the photofield effect, when electron-hole pairs generated in the band-bending region are swept away by the electric field ͑from applied gate voltage V G and drain voltage V D ͒.…”

Photoactive self-assembled monolayers for optically switchable organic thin-film transistors

“…[1][2][3][4] Since most organic materials applied in thin-film transistor devices are based on extended p-conjugated systems the absorption of visible light and the resulting photoconductive and photovoltaic effects may cause a strong impact on the device characteristics. 5,6 The understanding and the control of these effects are essential in order to prevent malfunction of the devices in ambient light. On the other hand, taking advantage of these features enables the realization of photosensitive transistors that can be used, e.g., for light detection and light induced switches.…”

“…On the other hand, taking advantage of these features enables the realization of photosensitive transistors that can be used, e.g., for light detection and light induced switches. [6][7][8][9][10][11][12] Among the different approaches to fabricate organic thinfilm transistors, the use of self-assembled monolayers as part of a thin hybrid dielectric has proven to be a promising route to realize flexible, low-power consuming organic thin-film transistors and circuits with a promising stability. 13,14 Moreover, it has been shown that applying molecules with electron acceptor functionality in a self-assembled monolayer (SAM) on a thick SiO 2 dielectric leads to a large photosensitivity in combination with pentacene as the semiconductor.…”

“…18 Thus, the photosensitivity of the drain current depends strongly on the gate voltage. 6 In the OFF-state, the increase of drain current upon illumination is dominated by the transition of photoinduced charge carriers into the dielectric due to the applied gate-field. In the ON-state, photo induced charges can contribute to the drain current.…”

Influence of film structure and light on charge trapping and dissipation dynamics in spun-cast organic thin-film transistors measured by scanning Kelvin probe microscopy

“…Several groups have reported a light response of organic thin films. 2,9,10,[34][35][36][37][38][39][40][41] Here, we show via SKPM that when the OTFT is illuminated with white light during the application of bias stress, the amount of trapped charge is diminished (Figure 3(a), (c)). An associated increase in I SD is also observed when the OTFT is illuminated (150 s after device is turned "ON").…”