The effect of deposition parameters and post treatment on the electrical properties of Mo thin films

In this study, we deposited low-resistivity molybdenum (Mo) thin films on soda-lime glass substrates with good adhesion. We adjusted various deposition parameters such as the sputtering power (52-102 W), working distance (5.5-9 cm) and annealing temperature (26-400 °C) to investigate their impact on the sheet resistance. By using a DC magnetron sputtering system, we obtained Mo thin films having the lowest sheet resistance of 0.190 Ω/□ with a sputtering power of 82 W, working distance of 6.5 cm, and annealing temperature of 400 °C; in addition, these films had good adhesivity. These Mo thin films were suitable for use as the Mo back contact in Cu(In,Ga)Se₂-based solar cells.     

Electronic transport and optical properties of thin oxide films

In this work, we present optical characterization of films of two transparent conductive oxides (ITO: indium tin oxide and ZnO: zinc oxide) including absorption coefficient and optical gap energy. We have also investigated the transport properties of ITO and ZnO films through measurements of electrical conductivity and thermoelectric power versus temperature. These measurements enabled us to investigate conduction mechanisms for metal-nonmetal transitions. Undoped ZnO thin films show a metal-semiconductor transition at temperatures beyond 350 K. We have conducted a similar study on ITO films where we demonstrated, for the first time, the existence of a conductivity transition below 400 K, which indicates a high absolute thermoelectric power at temperatures above the transition temperature.     

The effect of annealing on structural, electrical and optical properties of nanostructured ITO films prepared by e-beam evaporation

Tin doped indium oxide (ITO) thin films with composition of 9.42 wt% SnO₂ and 89.75 wt% In₂O_3, and impurities balanced on glass substrates at room temperature have been prepared by electron beam evaporation technique and then were annealed in air at different temperatures from 350 to 550 °C for 1 h. XRD pattern showed that increasing annealing temperature increased the crystallinity of thin films and at 550 °C high quality crystalline thin films with grain size of about 37 nm were obtained. Conductivity of ITO thin films was increased by increasing annealing temperature and conductivity obtained results in 350-550 °C temperature range were also excellently fitted in both Arrhenius-type and Davis-Mott variable-range hopping conductivity models. The UV-vis transmittance spectra were also confirmed that the annealing temperature has significant effect on the transparency of thin films. The highest transparency over the visible wavelength region of spectrum (93%) obtained at 550 °C on annealing temperature. It should be noted that this thin film was deposited on substrate at room temperature. This result obtained is equivalent with those values that have already been reported but with high-level (20 wt%) tin doped indium oxide thin films and also at 350 °C substrate temperature. The allowed direct band gap at the temperature range 350-550 °C was estimated to be in the range 3.85-3.97 eV. Band gap widening with an increase in annealing temperature was observed and is explained on the basis of Burstein-Moss shift. A comparison between the electron beam evaporation and other deposition techniques showed that the better figure of merit value can be obtained by the former technique. At the end we have compared our results with other techniques.     

Preparation of transparent conductive indium tin oxide thin films from nanocrystalline indium tin hydroxide by dip-coating method

Indium tin oxide (ITO) thin films with well-controlled layer thickness were produced by dip-coating method. The ITO was synthesized by a sol-gel technique involving the use of aqueous InCl₃, SnCl₄ and NH₃ solutions. To obtain stable sols for thin film preparation, as-prepared Sn-doped indium hydroxide was dialyzed, aged, and dispersed in ethanol. Polyvinylpyrrolidone (PVP) was applied to enhance the stability of the resulting ethanolic sols. The transparent, conductive ITO films on glass substrates were characterized by X-ray diffraction, scanning electron microscopy and UV-Vis spectroscopy. The ITO layer thickness increased linearly during the dipping cycles, which permits excellent controllability of the film thickness in the range ~ 40-1160 nm. After calcination at 550 °C, the initial indium tin hydroxide films were transformed completely to nanocrystalline ITO with cubic and rhombohedral structure. The effects of PVP on the optical, morphological and electrical properties of ITO are discussed.     

Laser patterning with beam shaping on indium tin oxide thin films of glass/plastic substrate

In this research the laser beam shaper component has been used to obtain top-hat intensity distribution laser beam to perform line scribing and to perform electrode patterning on Indium thin oxide (ITO) thin films deposited on glass and plastic substrate. ITO films were removed with third harmonic Nd:YAG laser processing system. The pulse duration, laser output power, pulse repetition rate and scanning speed parameters of straight line patterning and electrode patterning on different types of substrates were discussed, respectively. The experimental results are measured by optical microscope and scanning electron microscope to evaluate the processing parameters and surface properties of ITO thin films.     

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%.     

Porous nanostructured ZnO films deposited by picosecond laser ablation

Porous nanostructured polycrystalline ZnO films, free of large particulates, were deposited by picosecond laser ablation. Using a Zn target, zinc oxide films were deposited on indium tin oxide (ITO) substrates using a picosecond Nd:YVO₄ laser (8 ps, 50 kHz, 532 nm, 0.17 J/cm²) in an oxygen atmosphere at room temperature (RT). The morpho-structural characteristics of ZnO films deposited at different oxygen pressures (150–900 mTorr) and gas flow rates (0.25 and 10 sccm) were studied. The post-deposition influence of annealing (250–550 °C) in oxygen on the film characteristics was also investigated. At RT, a mixture of Zn and ZnO formed. At substrate temperatures above 350 °C, the films were completely oxidized, containing a ZnO wurtzite phase with crystallite sizes of 12.2–40.1 nm. At pressures of up to 450 mTorr, the porous films consisted of well-distinguished primary nanoparticles with average sizes of 45–58 nm, while at higher pressures, larger clusters (3.1–14.7 μm) were dominant, leading to thicker films; higher flow rates favored clustering.     

Pulsed laser deposition of indium tin oxide films on flexible polyethylene naphthalate display substrates at room temperature

Pulsed laser deposition was used to deposit high-quality indium tin oxide (ITO) thin solid films on polyethylene napthalate (PEN) flexible display substrates. The electrical, optical, microstructural, mechanical and adhesive properties of the functional thin layer were investigated as a function of a narrow range of background oxygen gas pressure at room temperature, which is the most desirable thermal condition for growing transparent conducting oxides on flexible display polymer substrates. ITO films (240 ± 35 nm thick) deposited on PEN at room temperature in the range of 0.33 to 2.66 Pa background oxygen pressure are observed to exhibit low electrical resistivity (~ 10^− 4 Ω cm) and high optical transmission (~ 90%). Electromechanical uniaxial tensile testing, of the hybrid thin structures, results in crack onset nominal strains of around 2%. The ITO surface adhesion reaches a maximum at 1.33 Pa deposition pressure.     

Effects of annealing temperature and heat-treatment duration on electrical properties of sol-gel derived indium-tin-oxide thin films

Transparent indium tin oxide (ITO) thin films have been deposited by the dip-coating process on silica substrates using solutions of 2,4-pentanedione, ethanol, indium and tin salts. The films have been first dried in air at 260 °C for 10 min and then annealed in a reducing atmosphere at different temperatures for various durations. The resistivity of ITO layers was found to decrease with increasing the metal concentration of the starting solution or the annealing temperature. Hence, by adjusting both metal concentration in the coating solution and heat-treatment, resistivities lower than 5 × 10^− 3 Ω cm for an annealing temperature of 550 °C and lower than 2 × 10^− 2 Ω cm for an annealing temperature of 300 °C, were obtained. These results are correlated with the density and the size of ITO grains in the films.     

Properties of Ce-doped ITO films deposited on polymer substrate by DC magnetron sputtering

Ce-doped indium tin oxide (ITO:Ce) films were deposited on flexible polyimide substrates by DC magnetron sputtering using ITO targets containing various CeO₂ contents (CeO₂ : 0, 0.5, 3.0, 4.0, 6.0 wt.%) at room temperature and post-annealed at 200 °C. The crystallinity of the ITO films decreased with increasing Ce content, and it led to a decrease in surface roughness. In addition, a relatively small change in resistance in dynamic stress mode was obtained for ITO:Ce films even after the annealing at high temperature (200 °C). The minimum resistivity of the amorphous ITO:Ce films was 3.96 × 10^− 4 Ωcm, which was deposited using a 3.0 wt.% CeO₂ doped ITO target. The amorphous ITO:Ce films not only have comparable electrical properties to the polycrystalline films but also have a crystallization temperature > 200 °C. In addition, the amorphous ITO:Ce film showed stable mechanical properties in the bended state.     

Optimization of indium tin oxide by pulsed DC power on single junction amorphous silicon solar cells

We investigated the optimal deposition conditions of a thin indium tin oxide (ITO) film on an amorphous silicon (a-Si) single-junction solar cell using pulsed DC magnetron sputtering. Thin ITO films were deposited while power, deposition time, pressure, gas flow and temperature were varied to find such conditions. The efficiency of a-Si solar cells with ITO films was 6.65% at the optimal conditions — a pulsed DC power of 40 W, a deposition time of 460 s, a pressure of 0.53 Pa, gas flow of 16 sccm and 151 °C. On the other hand, an a-SiGe tandem solar cell with the ITO films made at the optimal conditions yields an efficiency of 7.20%. We have also examined the surface morphology of ITO coated a-Si solar cells, using atomic force microscopy. Interestingly, a change in power does not alter the surface morphology at small length scales, whereas at large scales, the lower power sample had a lower surface roughness than the samples made with higher powers. We also find that for the range of deposition conditions examined, the value of the roughness exponent does not change with α ? 2/3 and a thin layer of ITO does not modify the surface morphology significantly.     

Femtosecond laser deposited zinc oxide film and its optical properties

Zinc oxide (ZnO) thin films have been grown on Si (100) substrates using a femto-second pulsed laser deposition (fsPLD) technique. The effects of substrate temperature and laser energy on the structural, surface morphological and optical properties of the films are discussed. The X-ray diffraction results show that the films are highly c-axis oriented when grown at 80 °C and (103)-oriented at 500 °C. In the laser energy range of 1.0 mJ-2.0 mJ, the c-axis orientation increases and the mean grain size decreases for the films deposited at 80 °C. The field emission scanning electron microscopy indicates that the films have a typical hexagonal structure. The optical transmissivity results show that the transmittance increases with the increasing substrate temperature. In addition, the photoluminescence spectra excited with 325 nm light at room temperature are studied. The structural properties of ZnO films grown using nanosecond (KrF) laser are also discussed.     

Low-temperature processing of transparent conductive indium tin oxide nanocomposites using polyvinyl derivatives

We report on the influence of additives on the electrical, optical, morphological and mechanical properties of transparent conductive indium tin oxide (In₂O₃:Sn; ITO) nanoparticle films by the use of polymers as matrix material. Key issues to fabricate layers suitable for use in electronic device applications are presented. Polyvinyl derivatives polyvinyl acetate, polyvinyl alcohol (PVA) and polyvinyl butyral were applied and their suitability to form transparent conductive ITO nanocomposite coatings at a maximum process temperature of 130 °C was investigated. A low-temperature treatment with UV-light has been developed to provide the possibility of curing ITO thin films deposited on substrates which do not withstand high process temperatures. Compared to best pure ITO layers (0.2 Ω^− 1 cm^− 1), the ITO-PVA nanocomposite coatings show a conductance value of 4.1 Ω^− 1 cm^− 1 and 5.9 Ω^− 1 cm^− 1 after reducing in forming gas. Sheet resistance of ca. 1200 Ω/□ with coexistent transmittance of 85% at 550 nm for a layer thickness of about 1.45 μm was achieved. The conductance enhancement is a consequence of nanoparticulate ITO network densification due to the acting shrinkage forces caused by the polymer matrix during film drying and additionally UV-induced crosslinking of PVA.     

Effects of sputtering pressure and Al buffer layer thickness on properties of AZO films grown by rf magnetron sputtering

Transparent and conductive Al-doped (2 wt.%) zinc oxide (AZO) films were deposited on inexpensive soda-lime glass substrates by using rf magnetron sputtering at room temperature. This study analyzed the effects of argon sputtering pressure, which varied in the range from 0.46 to 2.0 Pa, on the morphological, electrical and optical properties of AZO films. The only (0 0 2) diffraction peak of the film were observed at 2θ～34.45°, exhibiting that the AZO films had hexagonal ZnO wurtzite structure, and a preferred orientation with the c-axis perpendicular to the substrate. By applying a very thin aluminum buffer layer with the thickness of 2 nm, findings show that the electrical resistivity was 9.46 × 10⁻⁴ Ω-cm, and the average optical transmittance in the visible part of the spectra was approximately 81%. Furthermore, as for 10 nm thick buffer layer, the electrical resistivity was lower, but the transmittance was decreased.     

ZnO thin films prepared by pulsed laser deposition

Zinc oxide (ZnO) thin films were deposited on soda lime glass substrates by pulsed laser deposition (PLD) in an oxygen-reactive atmosphere. The structural, optical, and electrical properties of the as-prepared thin films were studied in dependence of substrate temperature and oxygen pressure. High quality polycrystalline ZnO films with hexagonal wurtzite structure were deposited at substrate temperatures of 100 and 300 °C. The RMS roughness of the deposited oxide films was found to be in the range 2-9 nm and was only slightly dependent on substrate temperature and oxygen pressure. Electrical measurements indicated a decrease of film resistivity with the increase of substrate temperature and the decrease of oxygen pressure. The ZnO films exhibited high transmittance of 90% and their energy band gap and thickness were in the range 3.26-3.30 eV and 256-627 nm, respectively.     

Study on physical properties of indium-doped zinc oxide deposited by spray pyrolysis technique

Transparent conducting indium doped zinc oxide (IZO) thin films have been deposited on soda-lime glass substrates by the spray pyrolysis technique. The structural, electrical, and optical properties of these films were investigated as a function of substrate temperature. In this work the substrate temperature was varied between 350 °C and 500 °C. X-ray diffraction pattern reveals that at 350 °C dominant peak is (100) orientation. By increasing substrate temperature from 350 °C to 450 °C, sheet resistance decreases, from 302 Ω/□ to 26 Ω/□, then at 500 °C increases to 34 Ω/□. In the useful range for deposition (i.e. 450 °C to 500 °C), the orientation of the films was predominantly (002). The lowest sheet resistance (26Ω/□) is obtained at substrate temperature of about 450 °C with the transmittance of about 75%. Study of scanning electron microscopy images shows that films deposited at 400 °C, have grain size as large as 574 nm, while with increasing substrate temperature to 450 °C, grain size becomes smaller and reaches to a value of about 100 nm with spherical shape. At 500 °C grain size value would be around 70 nm with the same spherical shape.     

Substrate temperature dependence of the properties of Ga-doped ZnO films deposited by DC reactive magnetron sputtering

Ga-doped zinc oxide (ZnO:Ga) transparent conductive films were deposited on glass substrates by DC reactive magnetron sputtering. The influence of substrate temperature on the structural, electrical, and optical properties of ZnO:Ga films was investigated. The X-ray diffraction (XRD) studies show that higher temperature helps to promote Ga substitution more easily. The film deposited at 350 °C has the optimal crystal quality. The morphology of the films is strongly related to the substrate temperature. The film deposited is dense and flat with a columnar structure in the cross-section morphology. The transmittance of the ZnO:Ga thin films is over 90%. The lowest resistivity of the ZnO:Ga film is 4.48×10⁻⁴ Ω cm, for a film which was deposited at the substrate temperature of 300 °C.     

Stability of nano-thick transparent conducting oxide films for use in a moist environment

The stability of nano-thick transparent conducting oxide thin films in a high humidity environment was investigated. The stability of ITO and impurity-doped ZnO thin films prepared with a thickness in the range from approximately 20 to 100 nm on glass substrates at a temperature below 200 °C by a pulsed laser deposition was evaluated in air at a relative humidity of 90% and a temperature of 60 °C. The resistivity of all Al- and Ga-doped ZnO thin films tested was found to increase markedly with test time, whereas that of ITO remained relatively stable; the stability (resistivity increase) of the doped ZnO thin films was considerably affected by film thickness but was relatively independent of the deposition substrate temperature. In particular, doped ZnO thin films with a thickness below approximately 50 nm were very unstable under the test conditions. The resistivity increase of doped ZnO films is mainly attributed to the grain boundary scattering resulting from the adsorption of oxygen on the grain boundary.     

Influence of oxygen pressure on the structural, electrical and optical properties of VO2 thin films deposited on ZnO/glass substrates by pulsed laser deposition

The influence of oxygen pressure on the structural and electrical properties of vanadium oxide thin films deposited on glass substrates by pulsed laser deposition, via a 5-nm thick ZnO buffer, was investigated. For the purposes of comparison, VO₂ thin films were also deposited on c-cut sapphire and glass substrates. During laser ablation of the V metal target, the oxygen pressure was varied between 1.33 and 6.67 Pa at 500 °C, and the interaction and reaction of the VO₂ and the ZnO buffer were studied. X-ray diffraction studies showed that the VO₂ thin film deposited on a c-axis oriented ZnO buffer layer under 1.33 Pa oxygen had (020) preferential orientation. However, VO₂ thin films deposited under 5.33 and 6.67 Pa were randomly oriented and showed (011) peaks. Crystalline orientation controlled VO₂ thin films were prepared without such expensive single crystal substrates as c-cut sapphire. The metal-insulator transition properties of the VO₂/ZnO/glass samples were investigated in terms of electrical conductivity and infrared reflectance with varying temperatures, and the surface composition was investigated by X-ray photoelectron spectroscopy.     

Study of the inductively coupled plasma assisted DC magnetron sputtering (ICPDMS) during ITO deposition

An inductively coupled plasma (ICP) assisted DC magnetron sputtering (ICPDMS) method for the deposition of indium tin oxide (ITO) thin films was developed to satisfy the challenging requirements of a room temperature process and high temperature durability. The resistivity of ITO thin films deposited by ICPDMS at room temperature was improved to as low as 1.2 × 10^− 2 Ω cm by increasing the RF power of the ICP source to 1200 W. Due to the additional dissociation and ionization by the high density plasma in ICPDMS system, the ITO thin films have a higher portion of Sn and oxygen atoms and a lower initial carrier concentration, ~ 10¹⁸ #/cm³, at room temperature than conventional ITO. However, the carrier concentration could be rapidly increased up to 10²⁰ #/cm³ by post-annealing to temperatures as high as 500 °C for 1 h under high vacuum conditions. Unlike conventional ITO, the electrical properties of ICPDMS-ITO were relatively unchanged after high temperature heat cycles, which is a very attractive property for high performance photovoltaic solar cell applications.