a b s t r a c tFour atmospheric pressure ozone oxidation methods were used to produce ultra-thin layers of aluminum oxide for organic thin-film transistors. They are UV/ozone oxidation in ambient (UV-AA) and dry (UV-DA) air, UV/ozone oxidation combined with high-voltage discharge-generated ozone in dry air (UV+O 3 -DA), and discharge-generated ozone in dry air (O 3 -DA). The lack of the high-energy UV photons during the O 3 -DA oxidation led to low relative permittivity and high leakage current density of the AlO x layer that rendered this method unsuitable for transistor dielectrics. Although this oxidation method led to the incorporation of oxygen into the film, the FTIR confirmed an increased concentration of the subsurface oxygen while the XPS showed the highest portion of the unoxidized Al among all four methods. The remaining three oxidation methods produced AlO x films with thicknesses in excess of 7 nm (2-h oxidation time), relative permittivity between 6.61 and 7.25, and leakage current density of (1-7) Â 10 À7 A/cm 2 at 2 MV/cm, and were successfully implemented into organic thin-film transistors based on pentacene and DNTT. The presence of -OH groups in all oxides is below the detection limit, while some carbon impurities appear to be incorporated.

No abstract

We report the results of an investigation into the contribution that trapping in interface states makes to the photovoltaic effect observed in organic phototransistors. To isolate this effect from other processes that occur in the transistor structure when under illumination, we focus attention on the photo-response of metal-insulatorsemiconductor (MIS) capacitors-the core structure of transistors. The capacitors comprised poly(3-hexylthiophene), (P3HT), as the active semiconductor in combination with one of three insulators, namely, poly (amide-imide), (PAI), SU-8 photoresist and polysilsesquioxane (PSQ). Following initial characterization in the dark, the capacitor response was measured both during and after irradiation with light in the wavelength range 400-700 nm. Three different approaches were employed to study the photo-response, each providing a different insight into the processes occurring. Capacitance-voltage sweeps before, during and after illumination provided direct evidence supporting the view that the photovoltaic effect occurred as a result of electron trapping in interface states of density up to ∼2 × 10 12 cm −2 in the P3HT/PAI combination but lower for SU-8 and PSQ. The dynamic photo-response, in which device capacitance was held constant by changing the applied bias, showed a fast component related to optically induced photoconduction in the semiconductor and a slower component reflecting the dynamics of interface electron trapping. Finally, photo-induced capacitance changes occurring with constant applied voltage were used to demonstrate a simple 3 × 3 imaging array.

No abstract

No abstract