Conductivity Of Doped Films Research Articles

Growth and Characterizations of Indium-Doped Pentacene Thinfilm Prepared by Thermal Co-Evaporation as a Novel Nanomaterial

This research is related to growth and characterizations of indium-doped pentacene thin films as a novel hybrid material. Doped films were prepared by thermal co-evaporation under high vacuum. The doping concentration was varied from 0% to 50% by controlling the different deposition rate between these two materials while the total thickness was fixed at 100 nm. The hybrid thin films were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD) and UV-Visible spectroscopy to reveal the physical and optical properties. Moreover, the electrical properties of ITO/indium-doped-pentacene/Al devices i.e. charge mobility and carrier concentration were determined by considering the relationship between current-voltage and capacitance-voltage. AFM results identify that doping of indium into pentacene has an effect on surface properties of doped films i.e. the increase of surface grain size. XRD results indicate that doping of metal into pentacene has an effect on preferential orientation of pentacene’s crystalline domains. UV-Vis spectroscopy results show evolution of absorbance at photon energy higher than 2.7 eV corresponding to absorption from oxide of indium formed in the films. Electrical measurements exhibit higher conductivity in doped films resulting from increment of both charge carrier mobility and carrier concentration. Furthermore, chemical interactions taken place inside the doped films were investigated by x-ray photoelectron spectroscopy (XPS) in order to complete the remaining questions i.e. how do indium atoms interact with the neighbor molecules?, what is the origin of the absorption at E > 2.7 eV? Further results and discussions will be presented in the publication.

Dependence of charge carrier mobility of 4,4′,4″-tris(N-3-methylphenyl-N-phenylamino)triphenylamine on doping concentration of tetrafluoro-tetracyano-quinodimethane

Electrical transport of pure and tetrafluoro-tetracyano-quinodimethane doped 4,4′,4″-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (m-MTDATA) films have been studied at various temperatures and doping concentrations. Pure films show space charge limited conduction with field and temperature dependent mobility. The J–V characteristics of doped m-MTDATA were ohmic at low voltages due to thermally released carriers from dopant states. At higher voltages the current density increases nonlinearly due to field dependent mobility and carrier concentration thereby filling of tail states of HOMO of the host. The conductivity of doped films were analysed using the Unified Gaussian Disorder Model (UGDM). The carrier concentration obtained from the fitting show a non-linear dependence on doping concentration which may be due to a combined effect of thermally activated carrier generation and increased carrier mobility.

Lightly Al-doped Ta 2O 5: Electrical properties and mechanisms of conductivity

Lightly Al-doped Ta2O5 films (10;15 nm) obtained by rf sputtering have been studied with respect to their dielectric and electrical properties. The formed metal–high-k dielectric–semiconductor capacitors have been characterized by capacitance–voltage and temperature-dependent current–voltage characteristics. It was established that the introduction of small amount (5 at.%) Al into the matrix of Ta2O5 improves dielectric constant, introduces negative oxide charge, suppresses deep oxygen-vacancy centers in Ta2O5 but creates shallow traps and changes the dominant conduction mechanism in the stacks. The doping produces more leaky films at room temperature and lower current at high temperature as compared to the case of pure Ta2O5. It is concluded that the strong contribution of tunneling processes through shallow traps in the conductivity of doped films could explain the observed current degradation at room temperature and its improved temperature stability at high temperatures. The energy levels of the traps responsible for the current transport are estimated.

Physical properties of polycrystalline Cr-doped SnO 2 films grown on glasses using reactive dc magnetron co-sputtering technique

Abstract Electrical, optical and magnetic properties of polycrystalline Cr-doped SnO2 films grown on glasses using reactive dc magnetron co-sputtering technique were investigated. The Cr content was modulated by varying the sputtering power applied on the Cr target. The carrier concentration and conductivity of doped films are reduced with increasing the Cr doping. Moreover, while the Cr content ratio Cr/(Sn + Cr) exceeds 0.9 at.%, the doped SnO2 films become insulators and the optical transmission is strongly affected. The surface roughness of sputtered films is also increased by Cr doping. The co-sputtered Cr-doped SnO2 films exhibit paramagnetic characteristics from room temperature down to 25 K.

Dielectric parameters and a.c. conductivity of pure and doped poly (methyl methacrylate) films at microwave frequencies

Dielectric properties of pure and doped poly (methyl methacrylate) (PMMA) films at microwave frequency, 8.92 GHz, have been studied at 35°C. Iodine, benzoic acid and FeCl3 have been used as dopants. The losses in doped films are found to be larger than in pure PMMA films. The increased losses account for increased a.c. conductivity in doped films. The increase in conductivity is accounted due to creation of additional hopping sites for the charge carriers in doped samples. The dielectric data has also been used to evaluate optical constants, absorption index (K) and refractive index (n) of the films.

Highly conductive free-standing films by electrochemical polymerisation of 3,4-dimethoxypyrrole

Abstract The electrosynthesis of high quality large area self-supporting films of poly(3,4-dimethoxypyrrole) tosylate by galvanostatic oxidation of the monomer in propylene carbonate-tributylammonium tosylate on stainless steel anodes is described. The material is characterised by complete elemental analysis, ESR and controlled potential spectroelectrochemistry. In dry acetonitrile, poly(3,4-dimethoxypyrrole) sustains hundreds of charging-discharging cycles without significant deterioration. The conductivity of doped films is equal to or greater than 200 S cm −1 with bipolarons as the main charge carriers. An unusual feature of the polymer are ESR spectroscopic g -values below 2.0.

Polymeric Organosilicon Systems. 26. Synthesis and Photochemical and Conducting Properties of Poly[(tetraethyldisilanylene)oligo(2,5-thienylenes)

A series of poly[(tetraethyldisilanylene)(2,5-thienylenes)n] (1−5) with n = 1−5 were synthesized. The NiCl2(dppe)-catalyzed Grignard coupling of 1,2-bis(5-bromothien-2-yl)tetraethyldisilane (6) and 1,2-bis(5‘-bromo-2,2‘-bithien-5-yl)tetraethyldisilane (7) with 1 equiv of Mg afforded polymer 2 (Mw = 53 000, 75% yield) and 4 (Mw = 29 500, 97% yield), respectively, while similar reaction of the di-Grignard reagent obtained from 6 and 7 with 1 equiv of 2,5-dibromothiophene afforded the respective polymers 3 (Mw = 47 000, 77% yield) and 5 (Mw = 17 000, 78% yield). The sodium condensation of 2,5-bis(chlorodiethylsilyl)thiophene afforded polymer 1 (Mw = 20 000, 32% yield). Irradiation of polymers 1−5 with a low-pressure mercury lamp resulted in cleavage of the silicon−silicon bonds, but the reactivity decreased with an increase in the number of thienyl units. When the films of polymers 2−5 were doped with FeCl3 vapor, conductivities of doped films were determined to be 10-5−10-3 S cm-1 (in vacuo).

Electric and magnetic field dependence of the conductivity in poly(3-hexylthiophene langmuir-blodgett films

Abstract The conductivity of undoped and NOPF 6 -doped Langmuir-Blodgett thin films of poly(3-hexylthiophene) has been studied under strong electric (up to 60 kV/cm) and magnetic (up to 15 T) fields at low temperatures (down to 4.3 K). The electric-field dependence of the conductivity in doped films fits the theory of charging-energy-limited tunneling between highly conducting regions. In the electric-field-induced conduction mode, the magnetoresistance adopts a positive B 2 dependence which is argued to arise from the geometrical contribution corresponding to an extremely high and bias-dependent Hall mobility, over 10 3 cm 2 /Vs below 40 K. However, the high Hall mobility was not measurable using a conventional four-point technique. The results can be reproduced in free-standing films of doped poly(3-hexylthiophene). Undoped Langmuir-Blodgett films show a linearly varying positive magnetoresistance the magnitude of which increases with decreasing temperature.