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Made available in DSpace on 2022-04-29T08:46:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Few works on solution-processed zinc oxide vertical transistors and electrolyte-gated transistors have shown the merits of both architectures. Here, we present an electrolyte-gated vertical field-effect transistor (EGVFET) based on a spray-deposited zinc oxide/silver nanowire (ZnO/AgNW) Schottky contact. The output curve shows that the device operates at a sub-1 V bias. Also, the electrolyte does not affect the diode cell, and the cyclic voltammetry of the capacitor cell does not indicate a faradic process between AgNW and the top-gate electrode. From the transfer curve, we extracted an ION/IOFF ratio of 104, an on-current density of 65.3 mA/cm2 and a normalized transconductance of 113.4 S/cm2. Our contribution places the ZnO-EGVFET structure on the front line to develop printed transistors without a high-resolution pattern. São Paulo State University – UNESP, Faculty of Science and Technology (FCT), Physics Department, Presidente Prudente, SP, Brazil. (e-mail: leonardo.nogueira@unesp.br) São Paulo State University – UNESP, Faculty of Science and Technology (FCT), Physics Department, Presidente Prudente, SP, Brazil. Universidade Federal do Paraná – UFPR, Physics Department, Curitiba, PR, Brazil. Universidade Tecnológica Federal Do Paraná – UTFPR, Physics Department, Curitiba, PR, Brazil.

The thermal, electrical and morphological characterization of poly(3-hexylthiophene-2,5diyl) (P3HT) is presented and discussed. Thermal analyses revealed high glass transition, melting and degradation temperatures, indicating high stability of the polymer to annealings in the range 25–200°C. Electrical measurements were performed in spin-coated devices constructed using indium tin oxide (ITO) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) in the sandwich structure ITO/PEDOT:PSS/P3HT/Al. The devices were thermally treated at 25°C, 100°C, 150°C, and 200°C prior to the measurements. Characteristic curves of current density versus voltage showed that the injection of charge carriers is governed by tunneling at high electric fields. Hole mobility was estimated by impedance spectroscopy, showing a maximum value of 8.6 × 10−5 cm2/Vs for annealed films at 150°C. A thermally stimulated current technique was used to analyze the trap density in the P3HT and its respective energies for all devices, presenting the lowest trap density for annealed films at 150°C. Morphological features observed by atomic force microscopy showed that the 150°C thermally treated film presents the best interface condition of the four investigated annealing temperatures.

The structural properties of amorphous GaSe9 thin films produced by vacuum evaporation were investigated using the EXAFS technique and the cumulant expansion method. Structural parameters such as average coordination numbers and interatomic distances, disorder and asymmetry of the partial pair distribution functions gij(r) were obtained and compared to those found in the amorphous GaSe9 alloy used as precursor in the evaporation technique. Results indicate that structural units present in GaSe9 evaporate without dissociation, showing the stability of this alloy.

Made available in DSpace on 2018-11-26T16:40:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-07-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) LNLS The eletronic and optical properties of amorphous GaSe thin films produced by vacuum evaporation were investigated using X-ray photoemission spectroscopy (XPS) and transmittance spectroscopy techniques. XPS measurements allowed the determination of the valence band energy and showed the chemical bonding and the charge transfer between Se and Ga atoms. Transmittance measurements allowed the determination of the optical gap, refractive index and extinction coefficient in the low and high absorption regions. Using the Wemple and DiDomenico single oscillator model we also found the oscillator and the dispersive energies. From the valence band and optical gap energies, the conduction band was found and an energy level diagram for f-GaSe is proposed. Fac Tecnol SENAI CIC, CIC, R Senador Accioly Filho 298, BR-81310000 Curitiba, PR, Brazil Univ Fed Parana, Dept Fis, Ctr Polit, BR-81531990 Curitiba, PR, Brazil UNIOESTE, Ctr Engn & Ciencias Exatas, BR-85903000 Toledo, PR, Brazil Univ Estadual Paulista, Dept Fis, BR-17033360 Bauru, SP, Brazil Univ Estadual Paulista, Dept Fis, BR-17033360 Bauru, SP, Brazil LNLS: SXS-10976

We report on the development and characterization of an all-organic vertical transistor, consisting of a p-type conjugated polymer, poly(bithiophene), as collector material, a poly(ethylene dioxythiophene)/poly(styrene sulfonate) layer as base material and a n-type molecule layer, Alq3, as emitter material. The transistor is operated under direct bias in the common-emitter mode, being its operation based upon charge recombination of the injected majority carriers at the emitter–base interface. Experimental results have yielded current amplification factors up to 7. We also demonstrate that tunneling controls the transport characteristics of the device.

In this work we present a permeable base transistor consisting of a 60 nm thick N,N'diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine layer or a 40 nm thick 2,6-diphenyl-indenofluorene layer as the emitter, a CalAl/Ca multilayer as the metal base, and p-Si as collector. In the base, the Ca layers are 5 nm thick and the Al layer was varied between 10 and 40 nm. the best results obtained with a 20 nm thick layer. The devices present common-base current gain with both organic layer and silicon acting as emitter, but there is only observable common-emitter current gain when the organic semiconductor acts as emitter. The obtained common-emitter current gain, similar to 2, is independent on collector-emitter voltage, base current and organic emitter in a reasonable wide interval. Air exposure or annealing of the base is necessary to achieve these characteristics, indicating that an oxide layer is beneficial to proper device operation.

A new organic semiconductor, 2,6-diphenylindenofluorene (DPIF), was synthesized in four steps with a high overall yield of 49.3%. The morphology of thin films of DPIF that were formed under different substrate temperatures was examined by atomic force microscopy and X-ray diffraction analysis. Two different crystalline phases were found to exist depending on the deposition conditions. The DPIF thin film emits around 500–530 nm, while the OLED based on DPIF emits green light with a maximum output over 150 Cd/m2 under 35 V. Two typical transistor devices, thin-film transistor (TFT) and semiconductor-metal-semiconductor (SMS) transistor, were fabricated and characterized. DPIF shows a weak n-type character from the TFT device measurement, while SMS transistors using DPIF as an emitter behave like permeable-base transistors with low operating voltages in both common-base and common-emitter modes and a feature of current amplification. Our results demonstrate however, that further research efforts are necessary in order to prevent the observed instabilities. These are quite important, considering that the common-emitter mode is widely used in applications requiring not only switching capability, but also current amplification.

We report on gallium–selenium alloy (GaSe9) thin films simultaneously functioning as both blocking layer and active layer on poly(3-hexylthiophene-2, 5-diyl) (P3HT)-based organic photodiodes in order to enhance device performance. In addition to improved transport of the photogenerated charge carriers, GaSe9 films also contribute to light absorption on a different wavelength interval than that of P3HT. Three different devices are compared: ITO/GaSe9/Al, ITO/P3HT/Al and ITO/P3HT/GaSe9/Al, with the last one presenting a lower dark current density (0.90 μA cm−2), higher ON/OFF current ratio (61) and fastest response under AM 1.5 light irradiance. The observed responsivity is 7.3 mA W−1 and is almost linearly dependent on irradiance in the range 0.6–60 W m−2. A maximum external quantum efficiency of 135% and specific detectivity of 16.7 × 1011 Jones at 390 nm incident light wavelength are obtained.

Selenium : phosphour (SeP) thin films produced by thermal sublimation in vacuum are used as hole injection layers (HILs) in tris(8-hydroxyquinolinato) aluminum (Alq3) based devices. These devices are constructed in the sandwich structure substrate/HIL/Alq3/Al using three different substrate electrodes: fluorine doped tin oxide, Au, and indium tin oxide. The obtained electrical measurements indicate a better injection of positive charge carriers using the SeP layer. Syncrotron radiation x-ray photoelectron experiments allowed the determination of the work function of SeP. The obtained value (Φ = 5.6 eV) is close to the HOMO energy level of Alq3 and is consistent with the better positive charge injection. The thermionic injection process is suggested to be responsible for the charge injection from the different substrate electrodes into the SeP material. From transmittance measurements it was possible to calculate the refractive index and absorption coefficient as a function of wavelength, and to estimate the optical band gap (Eg = 1.9 eV). The latter and the measured work function were used in the construction of an energy level diagram of the SeP thin films used as HILs in organic devices. The hole injection efficiency of the produced films are compared with results using poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT : PSS).