Ultrathin Al-doped transparent conducting zinc oxide films fabricated by pulsed laser deposition

Al-doped transparent conducting zinc oxide (AZO) films, approximately 20-110 nm-thick, were deposited on glass substrates at substrate temperatures between 200 and 300 °C by pulsed laser deposition (PLD) using an ArF excimer laser (λ = 193 nm). When fabricated at a substrate temperature of 260 °C, a 40-nm-thick AZO film showed a low resistivity of 2.61 × 10^− 4 Ω·cm, carrier concentration of 8.64 × 10²⁰ cm^− 3, and Hall mobility of 27.7 cm²/V·s. Furthermore, for an ultrathin 20-nm-thick film, a resistivity of 3.91 × 10^− 4 Ω·cm, carrier concentration of 7.14 × 10²⁰ cm^− 3, and Hall mobility of 22.4 cm²/V·s were obtained. X-ray diffraction (XRD) spectra, obtained by the θ-2θ method, of the AZO films grown at a substrate temperature of 260 °C showed that the diffraction peak of the ZnO (0002) plane increased as the film thickness increased from 20 to 110 nm. The full-width-at-half-maximum (FWHM) values were 0.5500°, 0.3845°, and 0.2979° for film thicknesses of 20, 40, and 110 nm, respectively. For these films, the values of the average transmittance in visible light wavelengths (400-700 nm) were 95.1%, 94.2%, and 96.6%, respectively. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) observations showed that even the 20-nm-thick films did not show island structures. In addition, exfoliated areas or vacant and void spaces were not observed for any of the films.     

High-rate synthesis of microcrystalline silicon films using high-density SiH4/H2 microwave plasma

A high electron density (> 10¹¹ cm^− 3) and low electron temperature (1-2 eV) plasma is produced by using a microwave plasma source utilizing a spoke antenna, and is applied for the high-rate synthesis of high quality microcrystalline silicon (μc-Si) films. A very fast deposition rate of ∼ 65 Å/s is achieved at a substrate temperature of 150 °C with a high Raman crystallinity and a low defect density of (1-2) × 10¹⁶ cm^− 3. Optical emission spectroscopy measurements reveal that emission intensity of SiH and intensity ratio of H_α/SiH are good monitors for film deposition rate and film crystallinity, respectively. A high flux of film deposition precursor and atomic hydrogen under a moderate substrate temperature condition is effective for the fast deposition of highly crystallized μc-Si films without creating additional defects as well as for the improvement of film homogeneity.     

Temperature dependence of Fluorine-doped tin oxide films produced by ultrasonic spray pyrolysis

Fluorine-doped tin oxide (FTO) films were prepared at different substrate temperatures by ultrasonic spray pyrolysis technique on glass substrates. Among F-doped tin oxide films, the lowest resistivitiy was found to be 6.2 × 10^− 4 Ω-cm for a doping percentage of 50 mol% of fluorine in 0.5 M solution, deposited at 400 °C. Hall coefficient analyses and secondary ion mass spectrometry (SIMS) measured the electron carrier concentration that varies from 3.52 × 10²⁰ cm^− 3 to 6.21 × 10²⁰ cm^− 3 with increasing fluorine content from 4.6 × 10²⁰ cm^− 3 to 7.2 × 10²⁰ cm^− 3 in FTO films deposited on various temperatures. Deposition temperature on FTO films has been optimized for achieving a minimum resistivity and maximum optical transmittance.     

ITO thin films deposited by advanced pulsed laser deposition

Indium tin oxide thin films were deposited by computer assisted advanced PLD method in order to obtain transparent, conductive and homogeneous films on a large area. The films were deposited on glass substrates. We studied the influence of the temperature (room temperature (RT)-180 °C), pressure (1-6 × 10^− 2 Torr), laser fluence (1-4 J/cm²) and wavelength (266-355 nm) on the film properties. The deposition rate, roughness, film structure, optical transmission, electrical conductivity measurements were done. We deposited uniform ITO thin films (thickness 100-600 nm, roughness 5-10 nm) between RT and 180 °C on a large area (5 × 5 cm²). The films have electrical resistivity of 8 × 10^− 4 Ω cm at RT, 5 × 10^− 4 Ω cm at 180 °C and an optical transmission in the visible range, around 89%.     

Influence of fluorine doping on structural, electrical and optical properties of spray pyrolysis ZnS films

ZnS films were deposited by spray pyrolysis on glass at 500 °C substrate temperature. In order to study the influence of fluorine on the properties of ZnS film, undoped and F-doped films were investigated using X-ray diffraction, scanning electron microscopy and optical transmittance spectroscopy. The absorption coefficient was measured and correlated with the photon energy to estimate the energy gap, which rises from 3.20 to 3.35 eV with increased F content. Carrier concentrations of our samples were determined from Hall effect measurements. It was found that the carrier concentration increases from 7.0 × 10¹² cm^− 3 to 8.0 × 10¹³ cm^− 3 with increasing F content from 0 to 6 wt.% in ZnS films.     

Effects of sputtering power and pressure on properties of ZnO:Ga thin films prepared by oblique-angle deposition

The effects of power and pressure on radiofrequency (RF) diode sputtering in oblique-angle (80°) deposition arrangement are presented. Oblique-angle sputtering of ZnO:Ga (GZO) thin films resulted in a tilted columnar crystalline structure and inclination of the c-axis by an angle of approximately 9° with respect to the substrate. This improved their structural, electrical and optical properties in comparison with films deposited perpendicularly to the substrate. GZO films sputtered by an RF power of 600 W at room temperature of the substrate in Ar pressure 1.3 Pa showed strong crystalline (002) texture, lowest electrical resistivity 3.4 × 10^− 3 Ωcm, highest electron mobility 10 cm² V^− 1 s^− 1, high electron concentration 1.8 × 10²⁰ cm^− 3 and good optical transparency up to 88%. The small inclination angle of the film structure is caused by the high kinetic energy of sputtered species and additional energetic particle bombardment causes random surface diffusion, which is suppressing the shadow effect produced by oblique-angle sputtering.     

Formation and characterization of thin films from phthalocyanine complexes: An electrosynthesis study using the atomic-force microscope

(μ-Cyano)(phthalocyaninato)metal(III) [PcMCN]_n species with a central transition metal ion, such as Fe(III) and Co(III), were used to prepare molecular films on a highly oriented pyrolytic graphite electrode substrate by using the cyclic voltammetry technique. In order to investigate the influence of the ligand on the film properties, 1,8-dihydroxyanthraquinone and 2,6-dihydroxyanthraquinone as bivalent ligands were employed. The structure of the molecular materials was analyzed by infrared spectroscopy. The in situ film formation, texture, composition and conductivity of each film were further investigated using atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and the four-probe technique, respectively. The [PcMCN]_n complexes provided conductive films with an electrical conductivity of 1 × 10^− 6 Ω^− 1 cm^− 1 at 298 K.     

Electrical, optical, and structural properties of InZnSnO electrode films grown by unbalanced radio frequency magnetron sputtering

We have investigated the electrical, optical, structural, and annealing properties of indium zinc tin oxide (IZTO) films prepared by an unbalanced radio frequency (RF) magnetron sputtering at room temperature, in a pure Ar ambient environment. It was found that the electrical and optical properties of unbalanced RF sputter grown IZTO films at room temperature were influenced by RF power and working pressure. At optimized growth condition, we could obtain the IZTO film with the low resistivity of 3.77 × 10^− 4 Ω cm, high transparency of ~ 87% and figure of merit value of 21.2 × 10^− 3Ω^− 1, without the post annealing process, even though it was completely an amorphous structure due to low substrate temperature. In addition, the field emission scanning electron microscope analysis results showed that all IZTO films are amorphous structures with very smooth surfaces regardless of the RF power and working pressure. However, the rapid thermal annealing process above the temperature of 400 °C lead to an abrupt increase in resistivity and sheet resistance due to the transition of film structure from amorphous to crystalline, which was confirmed by X-ray diffraction examination.     

Organic thin film transistor using silver electrodes by the ink-jet printing technology

We have developed a conductive ink containing silver nanoparticles from which the electrodes for organic thin film transistor were directly patterned by ink-jet printing. Nano-sized silver particles having ∼ 20 nm diameter was used for a direct metal printing. Silver conductive ink was printed on the heavily doped n-type silicon wafer with 200-nm thick thermal SiO₂ layer as a substrate. To achieve a high line resolution and smooth conductive path, the printing conditions such as the inter-drop distance, stage moving velocity and temperature of the pre-heated substrates were optimized. After the heat-treatment at temperatures of 200 °C for 30 min, the printed silver patterns exhibit metal-like appearance and the conductivity. To fabricate a coplanar type TFTs, an active material of semiconducting oligomer, α,ω-dihexylquaterthiophene (DH4T) in a chlorobenzene was deposited between the ink-jet printed silver electrodes by drop casting. The OTFT with the ink-jetted source/drain electrodes shows general performance characteristics with good saturation behavior and no significant contact resistance as compared to the one with vacuum deposited electrodes. The electrical characteristic parameters of OTFT show the mobility of 1.3 × 10^− 3 cm² V^− 1 s^− 1 in the saturation regime, on/off current ratio over 10³, and threshold voltage of about − 13 V.     

Fabrication and characterization of Ni-YSZ anode functional coatings by electron beam physical vapor deposition

Two kinds of NiO-YSZ (yttria-stabilized zirconia) coatings, respectively with uniform and gradient distributions of NiO content along the coating thickness direction, were prepared by electron beam physical vapor deposition (EB-PVD) via adjusting electron beam currents. Then uniform and graded Ni-YSZ coatings were obtained from corresponding NiO-YSZ coatings after a reduction treatment. For uniform Ni-YSZ coating, the composition and porosity distributions along the coating thickness were uniform. The specific surface area and total pore volume for this coating could reach up to 4.330  m² g ^− 1 and 0.0346  cm³ g ^− 1 respectively. The area specific resistance (ASR) of this coating kept increasing with the rise in temperature and an ASR of 2.1 × 10 ^− 5Ω cm² was obtained at 600 °C. For graded Ni-YSZ coating, a gradient in Ni content and porosity was realized along the coating thickness. A high porosity of up to 33% was achieved in the part of the coating close to the substrate, while a low porosity of 10% was obtained in the part close to coating surface.     

Chemical diffusion coefficient of lithium ion in Li3V2(PO4)3 cathode material

The kinetic properties of monoclinic lithium vanadium phosphate were investigated by potential step chronoamperometry (PSCA) and electrochemical impedance spectroscopy (EIS) method. The PSCA results show that there exists a linear relationship between the current and the square root of the time. The D?_Li values of lithium ion in Li_3-xV₂(PO₄)₃ under various initial potentials of 3.41, 3.67, 3.91 and 4.07 V (vs Li/Li⁺) obtained from PSCA are 1.26 × 10^− 9, 2.38 × 10^− 9, 2.27 × 10^− 9 and 2.22 × 10^− 9 cm²·s^− 1, respectively. Over the measuring temperature range 15-65 °C, the diffusion coefficient increased from 2.67 × 10^− 8 cm²·s^− 1 (at 15 °C) to 1.80 × 10^− 7 cm²·s^− 1 (at 65 °C) as the measuring temperature increased.     

Improved electrical properties of tin-oxide films by using ultralow-pressure sputtering process

The improved structural and electrical properties of tin-oxide films produced by using ultralow-pressure sputtering (ULPS) method are reported. The Hall mobility of the film (~ 13 cm²/V s) deposited using ULPS was about 1.5 times higher than that of the film (~ 8 cm²/V s) sputtered using a pressure of 4.0 × 10^− 1 Pa. As the sputtering pressure was decreased, the film was transformed from an amorphous structure to a nano-crystalline one and gained a stoichiometric SnO₂ composition. These changes in the film structure sufficiently decreased the carrier concentration to facilitate application to thin film transistors.     

Tungsten-doped ZnO transparent conducting films deposited by direct current magnetron sputtering

Highly conducting and transparent thin films of tungsten-doped ZnO (ZnO:W) were prepared on glass substrates by direct current (DC) magnetron sputtering at low temperature. The effect of film thickness on the structural, electrical and optical properties of ZnO:W films was investigated. All the deposited films are polycrystalline with a hexagonal structure and have a preferred orientation along the c-axis perpendicular to the substrate. The electrical resistivity first decreases with film thickness, and then increases with further increase in film thickness. The lowest resistivity achieved was 6.97 × 10⁻⁴ Ω cm for a thickness of 332 nm with a Hall mobility of 6.7 cm² V⁻¹ s⁻¹ and a carrier concentration of 1.35 × 10²¹ cm⁻³. However, the average transmittance of the films does not change much with an increase in film thickness, and all the deposited films show a high transmittance of approximately 90% in the visible range.     

Annealing effect on dielectric and leakage current characteristics of Mn-doped Ba0.6Sr0.4TiO3 thin films as gate insulators for low voltage ZnO thin film transistor

We report on the dielectric properties and leakage current characteristics of 3 mol% Mn-doped Ba_0.6Sr_0.4TiO₃ (BST) thin films post-annealed up to 600 °C following room temperature deposition. The suitability of 3 mol% Mn-doped BST films as gate insulators for low voltage ZnO thin film transistors (TFTs) is investigated. The dielectric constant of 3 mol% Mn-doped BST films increased from 24 at in-situ deposition up to 260 at an annealing temperature of 600 °C due to increased crystallinity and the formation of perovskite phase. The measured leakage current density of 3 mol% Mn-doped BST films remained on the order of 5 × 10^− 9 to 10^− 8 A/cm² without further reduction as the annealing temperature increased, thereby demonstrating significant improvement in the leakage current characteristics of in-situ grown Mn-doped BST films as compared to that (5 × 10^− 4 A/cm² at 5 V) of pure BST films. All room temperature processed ZnO-TFTs using a 3 mol% Mn-doped BST gate insulator exhibited a field effect mobility of 1.0 cm²/Vs and low voltage device performance of less than 7 V.     

Post deposition annealing temperature effect on silicon quantum dots embedded in silicon nitride dielectric multilayer prepared by hot-wire chemical vapor deposition

The preparations of the 20-period of a Si quantum dot (QD)/SiN_x multilayer in a hot-wire chemical vapor deposition (HWCVD) chamber is presented in this paper. The changes in the properties of Si-QDs after the post deposition annealing treatment are studied in detail. Alternate a-Si:H and SiN_x layers are grown in a single SiN_x deposition chamber by cracking SiH₄, and SiH₄ + NH₃, respectively at 250 °C. The as-deposited samples are annealed in the temperature range of 800 °C to 950 °C to grow Si-QDs. All the samples are characterized by confocal micro Raman, transmission electron microscope (TEM), and photoluminescence (PL) to study the changes in the film structures after the annealing treatment. The micro Raman analysis of the samples shows the frequency line shifting from 482 cm^− 1 to 500 cm^− 1 indicating the Si transition from an amorphous to a crystalline phase. The TEM micrograph inspection indicates the formation of Si-QDs of size 3 to 5 nm and a density of 5 × 10¹²/cm². The high resolution TEM micrographs show an agglomeration of Si-QDs with an increase in the annealing temperature. The PL spectra show a peak shifting from 459 nm to 532 nm with increasing the annealing temperature of the film.     

Contribution to carrier densities of the oxygen vacancy in a low-resistivity tin-doped indium oxide film by the hot-cathode plasma sputtering method

In order to clarify the contribution to carrier density by oxygen vacancies in tin-doped indium oxide (ITO) films prepared on glass substrates by the hot-cathode plasma sputtering method, we have investigated the effect of annealing on the electrical properties of an ITO film with a resistivity of 1.0 × 10^− 4 Ω cm. A drastic decrease in carrier density from 2.0 × 10²¹ to 0.88 × 10²¹ cm^− 3 was found with gradual increase in the Hall mobility from 29 to 35 cm² V^− 1 s^− 1 for repeated annealing cycles, when the ITO film was exposed for one hour to 400 °C oxygen gas at atmospheric pressure. The results indicate that the contribution of oxygen vacancies to carrier density was ca. 1.12 × 10²¹ cm^− 3 for the ITO film with an overall carrier density of 2.0 × 10²¹ cm^− 3.     

Self-consistent global model for inductively coupled Cl2 plasma: Comparison with experimental data and application for the etch process analysis

The investigations of the influence of gas pressure and input power on the Cl₂ plasma parameters in the inductively coupled plasma system were carried out. The investigations combined plasma diagnostics by Langmuir probe and plasma modeling using the self-consistent global model with Maxwellian approximation for electron energy distribution function. From the experiments, it was found that an increase of gas pressure in the range of 0.27-3.33 Pa at 400-700 W input power results in decreasing both electron temperature (3.3-2.0 eV) and density (6.6 × 10¹⁰ − 3.0 × 10¹⁰ cm^− 3 for 400 W and 1.2 × 10¹¹ − 6.4 × 10¹⁰ cm^− 3 for 700 W). The model showed an outstanding agreement with the experiments and provided the data on densities and fluxes of active species. These data combined with the model of etch kinetics demonstrated the possibility of different etch rate behaviors depending on the input process parameters as well as on the properties of the etched surface.     

Structural, electrical and optical properties of zirconium-doped zinc oxide films prepared by radio frequency magnetron sputtering

Transparent and conducting zirconium-doped zinc oxide films have been prepared by radio frequency magnetron sputtering at room temperature. The ZrO₂ content in the target is varied from 0 to 10 wt.%. The films are polycrystalline with a hexagonal structure and a preferred orientation along the c axis. As the ZrO₂ content increases, the crystallinity and conductivity of the film are initially improved and then both show deterioration. Zr atoms mainly substitute Zn atoms when the ZrO₂ content are 3 and 5 wt.%, but tend to cluster into grain boundaries at higher contents. The lowest resistivity achieved is 2.07 × 10^− 3 Ω cm with the ZrO₂ content of 5 wt.% with a Hall mobility of 16 cm² V^− 1 s^− 1 and a carrier concentration of 1.95 × 10²⁰ cm^− 3. All the films present a high transmittance of above 90% in the visible range. The optical band gap depends on the carrier concentration, and the value is larger at higher carrier concentration.     

Polycrystalline films of tungsten-doped indium oxide prepared by d.c. magnetron sputtering

Electrical and optical properties of polycrystalline films of W-doped indium oxide (IWO) were investigated. These films were deposited on glass substrate at 300 °C by d.c. magnetron sputtering using ceramic targets. The W-doping in the sputter-deposited indium oxide film effectively increased the carrier density and the mobility and decreased the resistivity. A minimum resistivity of 1.8 × 10^− 4 Ω cm was obtained at 3.3 at.% W-doping using the In₂O₃ ceramic targets containing 7.0 wt.% WO₃. The 2.2 at.% W-doped films obtained from the targets containing 5.0 wt.% WO₃, showed the high Hall mobility of 73 cm² V^− 1 s^− 1 and relatively low carrier density of 2.9 × 10²⁰ cm^− 3. Such properties resulted in novel characteristics of both low resistivity (3.0 × 10^− 4 Ω cm) and high transmittance in the near-infrared region.     

Nitrogen-doped p-type ZnO thin films and ZnO/ZnSe p-n heterojunctions grown on ZnSe substrate by radical beam gettering epitaxy

We investigate the p-type doping in ZnO prepared by the method of radical beam gettering epitaxy using NO gas as the oxygen source and nitrogen dopant. Secondary ion mass spectroscopy measurements demonstrate that N is incorporated into ZnO film in concentration of about 8 × 10¹⁸ cm^− 3. The hole concentration of the N-doped p-type ZnO films was between 1.4 × 10¹⁷ and 7.2 × 10¹⁷ cm^− 3, and the hole mobility was 0.9-1.2 cm²/Vs as demonstrated by Hall effect measurements. The emission peak of 3.312 eV is observed in the photoluminescence spectra at 4.2  of N-doped p-type ZnO films, probably neutral acceptor bound. The activation energy of the nitrogen acceptor was obtained by temperature-dependent Hall-effect measurement and equals about 145 meV. The p-n heterojunctions ZnO/ZnSe were grown on n-type ZnSe substrate and have a turn-on voltage of about 3.5 V.