Analysis of current-voltage and capacitance-voltage-frequency characteristics in Al/p-Si Schottky diode with the polythiophene-SiO2 nanocomposite interfacial layer

The current-voltage characteristic of the prepared Al/Polythiophene-SiO₂/p-Si Schottky diode was analyzed by using different methods at room temperature. The barrier height and ideality factor of the diode were determined by using the conventional current-voltage method as 0.729 eV and 2.12, respectively. The barrier height values calculated by means of the modified Norde functions have showed good agreement with the barrier height value obtained by using the current-voltage method. The series resistance which causes the electrical characteristics to be non-ideal was calculated from Cheung functions and the modified Norde functions. The energy distribution of the interface states has been determined from the forward-bias current-voltage data. The frequency dependence of the Schottky diode parameters obtained from capacitance-voltage characteristics has been analyzed.     

Charge conduction process and photovoltaic effects in thiazole yellow (TY) thin film based Schottky devices

The charge generation and photovoltaic effects observed with thin films of TY in the form of sandwich structures, were analysed by J-V, C-V and photoaction spectra. These measurements were explained in terms of n-type semiconductivity of TY thin film and by the formation of a Schottky barrier with ITO while Ohmic contact with an Al or In electrode. The existence of thermionic emission over the ITO-TY barrier has been observed in low voltage region, whereas at high voltages, the process is dominant by the series resistance of TY layer. Various electrical parameters were calculated from the analysis of J-V and C-V characteristics of the devices and discussed in details. The diode quality factor is higher for Al/TY/ITO than In/TY/ITO device which can be attributed to the formation of thin layer of Al₂O₃ between Al and TY. The photoaction spectra of the devices reveal that the fraction of light which is absorbed near the ITO-TY interface, to the depth of 180 Å, is responsible for producing the charge carriers. The photovoltaic parameters were also calculated from the J-V characteristics of the devices, under illumination and described in detail.     

Poly (3,4-ethylenedioxythiophene) (PEDOT) and poly (3,4-ethylenedioxythiophene)-few walled carbon nanotube (PEDOT-FWCNT) nanocomposite based thin films for Schottky diode application

Transparent, conductive films of poly (3,4-ethylenedioxythiophene) (PEDOT) and poly (3,4-ethylenedioxythiophene)-few walled carbon nanotube (PEDOT-FWCNT) nanocomposite were synthesized by in-situ oxidative polymerization and investigated for their Schottky diode property. The prepared films were characterized by UV–Vis spectroscopy, thermal gravimetric analysis (TGA), surface resistivity, cyclic voltametery, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). SEM reveals the formation of homogeneous and adhesive polymer films while HRTEM confirms the uniform wrapping of polymer chains around the nanotube walls for PEDOT-FWCNT film. Improved thermal stability, conductivity and charge storage property of PEDOT in the presence of FWCNT is observed. Among different compositions, 5 wt. % of FWCNT is found to be optimum with sheet resistance and transmittance of 500 Ω sq⁻¹ and 77%, respectively. Moreover, the electronic and junction properties of polymer films were studied and compared by fabricating sandwich type devices with a configuration of Al/PEDOT or PEDOT-FWCNT nanocomposite/indium tin oxide (ITO) coated glass. The measured current density-voltage characteristics show typical rectifying behavior for both configurations. However, enhanced rectification ratio and higher forward current density is observed in case of PEDOT-FWCNT based Schottky diode. Furthermore, reliability test depicts smaller hysteresis effect and better performance of PEDOT-FWCNT based diodes.     

Optical and electrical properties of p-type transparent conducting CuAlO2 thin film

P-type transparent conducting CuAlO₂ thin films were prepared by e-beam evaporation and wet-oxidation technique. CuAlO₂ film was preferentially (006) oriented after wet-oxidation. The transmittance varied from 20 to 85% and the resistivity varied from 5 × 10^− 3 to 4 Ω cm with wet-oxidation conditions. The nature of p-type films was confirmed by the positive hall coefficient. Optical band gap was estimated to be in the range of 3.96-4.20 eV. These behaviors were due to the decrease of oxygen deficient state in the film as oxidation progresses. Microstructural observations of films showed smooth morphology with 23.2-29.7 Å rms roughness.     

The effect of rapid thermal annealing on structural and electrical properties of TiB2 thin films

This work reports on the effect of post-deposition rapid thermal annealing on the structural and electrical properties of deposited TiB₂ thin films. The TiB₂ thin films, thicknesses from 9 to 450 nm, were deposited by e-beam evaporation on high resistivity and thermally oxidized silicon wafers. The resistivity of as-deposited films varied from 1820 μΩ cm for the thinnest film to 267 μΩ cm for thicknesses greater than 100 nm. In the thickness range from 100 to 450 nm, the resistivity of TiB₂ films has a constant value of 267 μΩ cm.

A rapid thermal annealing (RTA) technique has been used to reduce the resistivity of deposited films. During vacuum annealing at 7 × 10⁻³ Pa, the film resistivity decreases from 267 μΩ cm at 200 °C to 16 μΩ cm at 1200 °C. Heating cycles during RTA were a sequence of 10 s. According to scanning tunneling microscopy analysis, the decrease in resistivity may be attributed to a grain growth through polycrystalline recrystallization, as well as to an increase in film density.

The grain size and mean surface roughness of annealed films increase with annealing temperature. At the same time, the conductivity of the annealed samples increases linearly with grain size. The obtained results show that RTA technique has a great potential for low resistivity TiB₂ formation.     

Enhanced dielectric and ferroelectric properties induced by TiO2@MWCNTs nanoparticles in flexible poly(vinylidene fluoride) composites

Flexible polymer based composites containing multi-walled carbon nanotubes (MWCNTs) have been reported to present high dielectric constant. However, the composites generally exhibit high dielectric loss and low dielectric breakdown strength, which prohibits their practical use in electronic and electric industry. MWCNTs were coated with a continuous layer of TiO₂ nanoparticles (TiO₂@MWCNTs) by a simple hydrothermal process and TiO₂@MWCNTs/poly(vinylidene fluoride) (PVDF) composites were prepared by a solution casting method. Compared to the pristine MWCNTs/PVDF composites, the TiO₂@MWCNTs/PVDF composites presented enhanced dielectric constant and lower dielectric loss. Additionally, the breakdown strength of the TiO₂@MWCNTs/PVDF composites was also improved, which is favorable for enhanced ferroelectric properties in the composites.     

Preparation and characterization of conducting poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) Langmuir-Blodgett film

The self-assembly of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) nanoparticles at an air/water interface was achieved by means of the electrostatic force between an octadecylamine (ODA) monolayer and PEDOT-PSS nanoparticles. A surface pressure (π)-area (A) isotherm and X-ray photoelectron spectroscopy of the composite film were used to confirm the electrostatic force between the SO₃⁻ group of PSS and the NH₄⁺ group of aliphatic amines. Monolayer and multilayer composite films of ODA/PEDOT-PSS and ODA-stearic acid (SA)/PEDOT-PSS were fabricated. These solid Langmuir-Blodgett films were investigated by the UV-Vis spectrum, atomic force microscopy, and X-ray diffraction method. It is observed that ODA-SA/PEDOT-PSS films had a higher film-forming capability than ODA/PEDOT-PSS films and an ordered multilayer structure was developed. The conductive properties of ODA-SA/PEDOT-PSS LB films were investigated in detail. Factors influencing the film conductivity such as the layer number and surface pressure were discussed and the conductive mechanism was also studied.     

Generation of electrical defects in ion beam assisted deposition of Cu(In,Ga)Se2 thin film solar cells

Thin films of Cu(In,Ga)Se₂ (CIGS) absorber layers for thin film solar cells have been manufactured on polyimide foil in a low temperature, ion beam assisted co-evaporation process.In the present work a set of CIGS thin films was produced with varying selenium ion energy. Solar cell devices have been manufactured from the films and characterized via admittance spectroscopy and capacitance-voltage profiling to determine the influence of the selenium ion energy on the electric parameters of the solar cells. It is shown that the impact of energetic selenium ions in the CIGS deposition process leads to a change in the activation energy and defect density and also in the spatial distribution of electrically active defects.For the interpretation of the results two defect models are taken into account.     

Experimental investigation of dimension effect on electrical oscillation in planar device based on VO2 thin film

In this paper, we report on an experimental analysis of dimension effect on a room-temperature electrical oscillation in a planar device using vanadium dioxide (VO₂) thin film. We investigate the variation of the oscillation current (I_O) and frequency (f_O) due to the variation of the dimension of the VO₂ devices, i.e., the length and width of the current channel of the device. For five different VO₂ devices with different dimensions, I_O and f_O are observed at room temperature in a simple circuit composed of a dc voltage source and a standard resistor including one of the VO₂ devices. From the experimental investigation, it is concluded that the peak-to-peak amplitude of I_O and f_O decrease with the increase of the length and width of the current channel. This indicates that f_O depends on not only the external source voltage but also the device dimension.     

The OFF to ON switching time and ON state consolidation in write-once-read-many-times memory devices based on doped and undoped carbon-sphere/polymer composites

We investigate the write operation in memory devices prepared using thin films of carbon spheres and cross-linked poly(4-vinylphenol) composites. Three types of carbon-spheres (N-doped, B-modified and undoped spheres) are used and their influence on memory characteristics is discussed. These memory devices show write-once-read-many-times (WORM) characteristics with an OFF to ON (high resistance to low resistance) transition at low voltages, of ca. 2 V. We investigate the ON-current, OFF-current and ON to OFF current ratio of devices prepared with composites of the three types of carbon spheres. The results are presented for devices prepared with three different carbon sphere concentration, for each carbon sphere type. The OFF to ON transition occurs in less than 1 μs and the ON-state in the best case is consolidated in less than 10 μs, for a write-operation voltage of 5 V.     

Interfacial chemistry control in thin film solar cells based on electrodeposited CuIn(S,Se)2

In this work, we present a study on CuIn(S,Se)₂ absorbers prepared by electrodeposition followed by rapid thermal annealing promising to lower manufacturing cost. However the annealed material contains copper sulpho-selenide of Cu(S_y,Se_1 − y) type which is harmful for the electrical properties of photovoltaic devices. These phases are removed by a cyanide etching. Because of an intrinsic variability of absorber fabrication process, the presented survey is based on statistic approach. We highlighted the influence of a cyanide treatment on surface and bulk compositions. The surface composition follows a distribution according to a Cu(S,Se)-CuIn(S,Se)₂ system and the bulk composition agrees with Cu(S,Se)₂-CuIn₃(S,Se)₅ system. Moreover, surface composition can be modified by adjusting the cyanide concentrations of etching solution without any changes in the bulk one. It ensues that Cu(S,Se) is not only present on the surface but also in the bulk of samples.     

The investigation of (Bi,La)(Ga,Fe)O3-PbTiO3 thin film prepared by PLD technique

In this report, (Bi,La)(Ga,Fe)O₃-PbTiO₃ (BLGF-PT) thin film was prepared on platinum coated Si wafer by pulsed laser deposition (PLD) method. BLGF-PT ceramic with morphotropic phase boundary (MPB) composition was used as the PLD target. The spot of Bi₂Fe₄O₉ impurity phase in X-ray diffraction profile implies a composition deviation in the BLGF-PT thin film from that of target. However, the MPB feature of co-existence of rhombohedral and tetragonal phases remains remarkable in the film. The characterization results of the leakage current and ferroelectric hysteresis loop indicate a desirable insulation in this BLGF-PT thin film. Polarization response by positive-up-negative-down pulse measurement and retention property are further carried out at room temperature to check the intrinsic ferroelectric performance. Moreover, high Curie temperature of 465 °C has been discovered in this BLGF-PT thin film, which may promote the application scope of the thin film.     

Formation of TiO2 domains in Poly (9-vinylcarbazole) thin film by hydrolysis-condensation of a metal alkoxide

New organic-inorganic hybrid thin films based on Poly (9-vinylcarbazole) (P9VK) and Dioxide titanium (TiO₂) bulk-heterojunction were obtained by a hydrolysis-condensation (H-C) process of titanium (IV) isopropoxide in thin film. The TiO₂ distribution in the film was investigated by scanning electron microscopy. The results indicated that homogeneous TiO₂ particles around 100 nm were formed on the surface of the polymer thin film. Photoluminescence spectroscopy has been used to study the charge transfer efficiency in the photoactive layer and results were compared with a simplest elaboration route, the dispersion of TiO₂ anatase in a P9VK solution before spin coating. Results showed that TiO₂ elaborated by H-C exhibits a competitive quenching effect with TiO₂ anatase.     

Room temperature multiferroic properties of (Bi0.95La0.05)(Fe0.97Mn0.03)O3/NiFe2O4 double layered thin film

(Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film was prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. X-ray diffraction and Raman scattering spectroscopy studies confirmed the formation of the distorted rhombohedral perovskite and the inverse spinel cubic structures for the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film. The (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film exhibited well saturated ferromagnetic (2 M_r of 18.1 emu/cm³ and 2H_c of 0.32 kOe at 20 kOe) and ferroelectric (2P_r of 60 μC/cm² and 2E_c of 813 kV/cm at 866 kV/cm) hysteresis loops with low order of leakage current density (4.5 × 10⁻⁶ A/cm² at an applied electric field of 100 kV/cm), which suggest the ferroelectric and ferromagnetic multi-layers applications in real devices.     

Preparation, electrical and optical properties of (Pb,Ca)TiO3 thin films using a modified sol-gel technique

Calcium modified lead titanate sol was synthesized using lead acetate trihydrate, calcium nitrate tetrahydrate and titanium tetra-n-butoxide as starting materials, methanol and ethanolamine were selected as solvent and stabilizing or complexing agent, respectively. (Pb_0.76Ca_0.24)TiO₃ thin films were prepared on platinum-coated silicon and fused silica substrates with the solution using the spinning method. The surface morphology and crystal structure, surface compositions and chemical states, electrical and optical properties of the thin films were investigated. The films have good composition homogeneity and thickness uniformity. The dielectric constant and dissipation factor of 1 kHz at room temperature were found to be 280 and 0.027, respectively, for thin films with 0.5 μm thickness annealed at 600°C for 1 h. The remanent polarization and coervive field were 15 μC/cm² and 64 kV/cm, respectively. The thin films exhibited good optical transmissitivity, and had optical direct transitions. The dispersion relation of refractive index and wavelength followed the single electron oscillation model. The band gap of the film which annealed at 650°C was 3.68 eV. The results also confirmed that ethanolamine was very effective in preparing uniform and dense oxide films, owing to the superior stability of the sols during hydrolytic polycondensation.     

Role of La0.5Sr0.5CoO3 template layers on dielectric and electrical properties of pulsed-laser ablated Pb(Nb2/3Mg1/3)O3-PbTiO3 thin films

Relaxor ferroelectric thin films of 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-PT) deposited on platinized silicon substrates with and without template layers were studied. Perovskite phase (80% by volume) was obtained through proper selection of the processing conditions on bare Pt/Ti/SiO₂/Si substrates. The films were initially grown at 300 °C using pulsed-laser ablation and subsequently annealed in a rapid thermal annealing furnace in the temperature range of 750-850 °C to induce crystallization. Comparison of microstructure of the films annealed at different temperatures showed change in perovskite phase formation and grain size etc. Results from compositional analysis of the films revealed that the films initially possessed high content of lead percentage, which subsequently decreased after annealing at temperature 750-850 °C. Films with highest perovskite content were found to form at 820-840 °C on Pt substrates where the Pb content was near stoichiometric. Further improvement in the formation of perovskite PMN-PT phase was obtained by using buffer layers of La_0.5Sr_0.5CoO₃ (LSCO) on the Pt substrate. This resulted 100% perovskite phase formation in the films deposited at 650 °C. Dielectric studies on the PMN-PT films with LSCO template layers showed high values of relative dielectric constant (3800) with a loss factor (tan δ) of 0.035 at a frequency of 1 kHz at room temperature.     

Electron transport in InGaO3(ZnO)m (m=integer) studied using single-crystalline thin films and transparent MISFETs

We have investigated the characteristics of transparent metal-insulator-semiconductor field-effect transistors (MISFETs) fabricated using InGaO₃(ZnO)_m (m=integer) single-crystalline thin films as n-channel layers and amorphous alumina as gate insulator films. The MISFETs exhibit good characteristics such as insensitivity to visible light illumination, off-current as low as ∼1 nA with a positive threshold voltage of ∼3 V and on/off current ratio of 10⁵. The field-effect mobility increased from ∼1 to ∼10 cm² (V s)⁻¹ as the m-value increased. Room temperature Hall mobility also increased. However, unexpectedly these values were lower than the field-effect mobility. It is explained by existence of shallow localized state in the homologous compounds.     

Influence of an additional carbon layer at the back contact-absorber interface in Cu(In,Ga)Se2 thin film solar cells

For paste-coated Cu(In,Ga)Se₂ (CIGS) absorber layers used for thin film solar cells one often gets a residual carbon layer between back contact and absorber layer. We investigate the influence of this layer on the solar cells’ performance with co-evaporated CIGS absorbers and find a beneficial effect. The power conversion efficiencies of thin chalcopyrite absorber layers are often limited by the influence of back contact recombination. It is assumed that the carbon layer between the back contact and the absorber layer helps lower this recombination and allows higher open circuit voltages and thus higher conversion efficiencies.     

SiO2 thin film deposition on the inner surface of a poly(tetra-fluoroethylene) narrow tube by atmospheric-pressure glow microplasma

SiO₂ thin films were deposited on the inner surfaces of a commercial poly(tetrafluoroethylene) narrow tube with an inner diameter of 0.5 mm using tetraethoxysilane/O₂ feedstock gases and He carrier gas by atmospheric-pressure microplasma-enhanced chemical vapor deposition. A glow microplasma was generated inside the tube by radio frequency (RF) capacitively coupled discharge. X-ray photoelectron spectroscopy spectra showed that the tube inner surface was covered by a SiO₂ thin film. Transparent SiO₂ thin films were obtained with a deposition rate of 230 nm/min at an RF power of 6 W and substrate temperature of 100 °C. The wettability of the SiO₂-coated tube was about 3 times as large as that of an untreated sample tube.     

Electronic transport properties of 1-(p-R-phenacyl)-4-{[(1′-ethylcarboxylate)-(3′-p-R′-phenacyl)]-7′-indolizinyl}pyridinium bromides in thin films

The temperature dependences of electrical conductivity, σ, and Seebeck coefficient, S, for some new pyridium monoquaternary salts derivatives, 1-(p-R-phenacyl)-4-{[(1′-ethylcarboxylate)-(3′-p-R′-phenacyl)]-7′-indolizinyl}pyridinium bromides have been studied.The film samples (d = 0.08-0.28 μm) have been deposited onto glass by an immersion technique (dimethylformamide was used as a solvent).The investigated compounds behave as typical p-type polycrystalline semiconductors. The activation energy of electrical conduction ranged between 0.65 and 1.72 eV, while the ratio of charge carrier mobilities laid in the range (0.60-0.83).The model based on band gap representation is suitable in explaining the electronic transport in present compounds in the higher temperature range (385-500 K).