Electrical and optical studies of transparent conducting ZnO:Al thin films by magnetron dc sputtering

Transparent conducting aluminium-doped Zinc oxide (ZnO:Al) films have been deposited on glass substrates by magnetron dc sputtering using a ceramic target (ZnO with 2 wt% Al₂O₃). The dependence of the electrical and optical properties of these films on substrate temperature, sputtering pressure of Ar and location of substrates were investigated in detail. Target is perpendicular with substrate and we controlled the distance ‘x’ of target and substrate. Optimized films with resistivity of 3.7?×?10^?4 Ω cm, an average transmission in the visible range (300–800 nm) of greater than 85% and the reflectance in the infrared range being greater than 85% have been formed. Substrate temperature, distance ‘x’, and working pressure are optimized for lower resistivity and high concentration of carriers.     

Effects of the O2/Ar gas flow ratio on the electrical and transmittance properties of ZnO:Al films deposited by RF magnetron sputtering

ZnO:Al thin films for transparent conductors were deposited on sapphire (0001) substrates by using an RF magnetron sputtering technique. Effects of the O₂/Ar flow ratio in the sputtering process on the crystallinity, carrier concentration, carrier mobility, and transmittance of the films were investigated. The FWHM of the (002) XRD intensity peak is minimal at the O₂/Ar flow ratio of 0.5. According to the Hall measurement results the carrier concentration and mobility of the film decrease and thus the resistivity increases as the O₂/Ar flow ratio increases. The transmittance of the ZnO:Al film deposited on the glass substrate is characteristic of standing wave. The transmittance increases as the O₂/Ar flow ratio in-RF magnetron sputtering increases up to 0.5. Considering the effects of the the O₂/Ar flow ratio on the electrical resistivity and transmittance of the ZnO:Al film the optimum O₂/Ar flow ratio is 0.5 in the RF magnetron sputter deposition of the ZnO:Al film.     

Study on the electrical and optical properties of ITO and AZO thin film by oxygen gas flow rate

Transparent conductive oxide (TCO) thin films such as tin doped indium oxide (ITO), zinc doped indium oxide (IZO) and Al doped zinc oxide (AZO) have been widely used as transparent electrode for display. ITO and AZO thin films for display was prepared by the facing targets sputtering (FTS) system. The FTS method is called a plasma-free sputter method because the substrate is located apart from plasma. This system can deposit the thin film with low bombardment by high energetic particles in plasma such as γ-electrons, negative ions and reflected Ar atoms. ITO and AZO thin films were deposited on glass substrate at room temperature with oxygen gas flow rate and input power. And the electrical, structural and optical properties of the thin films were investigated. As a result, the resistivity of ITO, AZO thin film is 6?×?10^?4 Ω cm, 1?×?10^?3 Ω cm, respectively. And the optical transmittance of as-deposited thin films is over 80% at visible range.     

Effect of fluorine doping on the properties of ZnO films deposited by radio frequency magnetron sputtering

ZnO films with varying fluorine content were prepared on Corning glass by radio frequency magnetron sputtering of ZnO target containing ZnF₂ at room temperature, and the compositional, electrical, optical, and structural properties of the as-grown films together with the vacuum-annealed films were investigated. The fluorine content in the fluorine doped ZnO (FZO) films increased almost linearly with increasing ZnF₂ content in sputter target, and the highest atomic concentration was 7.3%. Vacuum-annealing caused a slight reduction of fluorine content in the films. The resistivity of the as-grown FZO films deposited showed a typical valley-like behavior with respect to the fluorine content in film, i.e. having minimum resistivity at intermediate fluorine content. Despite high fluorine content in the FZO films, the carrier concentration remained below 1.2?×?10²⁰ cm^?3, leading to very low doping efficiency level. Upon vacuum-annealing, the resistivity of FZO films decreased substantially due to increase in both the carrier concentration and the Hall mobility. From the structural analysis made by X-ray diffraction study, it was shown that addition of small amount of fluorine enhanced the crystallinity of FZO films with (002) preferred orientation, and that large amount of fluorine addition yielded disruption of preferred orientation. It was also shown that doping of fluorine rendered a beneficial effect in reducing the absorption loss of ZnO films in visible range, thereby substantially enhancing the figure of merit.     

氧气分压和衬底温度对铝掺杂氧化锌透明导电薄膜性能的影响（英文）

通过直流磁控溅射法在玻璃衬底上制备了一系列铝掺杂氧化锌透明导电薄膜,研究了氧气分压和衬底温度对铝掺杂氧化锌透明导电薄膜的结构和光电性能的影响。X-射线衍射研究表明铝掺杂氧化锌薄膜是沿c-轴方向堆积的具有六方结构的多晶薄膜,实验获得的最佳沉积衬底温度和氧分压分别为400℃和5∶100(O_2/Ar),在该条件下制备的铝掺杂氧化锌薄膜具有较低的表面电阻(80Ω/sq)和较高的平均透过率(80%)。     

Effect of discharge power density on the properties of Al and F co-doped ZnO thin films prepared at room temperature

ZnO transparent conducting thin films co-doped with aluminium and fluorine (AZO:F) were prepared on glass substrates by RF magnetron sputtering at room temperature. The effect of discharge power density on the microstructure, surface morphology, electrical and optical properties was investigated. From XRD analysis, it was revealed that the intensity of (002) favoured orientation of ZnO films increased with power density from 2.6 to 6.1?W/cm² and then turned to a randomly orientated structure as power density continuously increased to 7.8?W/cm². The film prepared at 6.1?W/cm² showed a better crystallization and microstructure with larger, pyramid-like grains that were approximately 180?nm long and 90?nm wide. As a result, the electrical resistivity of the AZO:F films had a minimum of 4.1?×?10^?4???cm. The improvement in the electrical resistivity of AZO:F films was due to the increase in carrier concentration from 8.8?×?10²⁰ to 1.38?×?10²¹?cm^?3 and the mobility from 5.8 to 11.8?cm² V^?1 s^?1. The increase in carrier concentration with power density was also found to affect the optical property of the films due to the Moss-Burstein shift.     

Effect of heat treatment of sputter deposited ZnO films co-doped with H and Al

ZnO films co-doped with H and Al (HAZO) were prepared by sputtering ZnO targets containing Al₂O₃ dcontent of 1 (HA₁ZO series) and 2 wt.% (HA₂ZO series) on Corning glass (Eagle 2000) at substrate temperature of 150 °C with Ar and H₂/Ar gas mixtures. The effects of hydrogen addition to Al-doped ZnO (AZO) films with different Al contents on the electrical, optical and structural properties of the as-grown films as well as the vacuum- and air-annealed films were examined. For the as-deposited films, the free carrier number in both series of HAZO films increased with increasing H₂ content in sputter gas. HA₂ZO film series prepared from target containing 2 wt.% Al₂O₃ showed better crystallinity and higher carrier concentration than HA₁ZO film series deposited using target containing 1 wt.% Al₂O₃. The crystallinity and the Hall mobility of HA₂ZO film series decreased with increasing H₂ content in sputter gas, while those of HA₁ZO film series showed a reversed behavior. Although HA₂ZO film series yielded lower resistivity than HA₁ZO film series due to higher carrier concentrations, the higher figure of merit (expressed as 1?/?ρα, where ρ and α represents the resistivity and absorption coefficient, respectively) was observed for HA₁ZO film series because of substantially low absorption loss in these films. When annealed in air ambient, HA₁ZO film series showed much stronger stability than HA₂ZO film series. Vacuum-annealing resulted in drop of the carrier concentrations as well as large shrinkage in lattice constant, which indicated that the hydrogen dopants are in relatively volatile state and can be removed easily from the films upon annealing.     

Effect of a hydrogen ratio in electrical and optical properties of hydrogenated Al-doped ZnO films

This study examined the effect of the hydrogen ratio on the electrical and optical properties of hydrogenated Al-doped zinc oxide (AZO) thin films deposited by rf magnetron sputtering using a ceramic target (98 wt% ZnO, 2 wt% Al₂O₃). Various AZO films on glass were prepared by changing the H₂/(Ar?+?H₂) ratio at room temperature. The AZO/H films showed a lower resistivity and a higher carrier concentration and mobility than the AZO films. However, the resistivity and mobility of the AZO/H films increased and decreased with increasing H₂ flow ratio, respectively. As a result, the AZO/H films grown with 2% H₂ addition showed excellent electrical properties with a resistivity of 4.98?×?10⁴ Ωcm. The UV-measurements showed that the optical transmission of the AZO/H films was >85% in the visible range with a wide optical band gap. In addition, the effect of H₂ flow ratio on the structure and composition of hydrogenated AZO thin films have also been studied.     

Spectroscopic ellipsometric determination of optical properties of V-Al co-doped ZnO films by rf magnetron sputtering

Zn_0.9?xV_0.1Al_xO aerogel nanopowders were prepared in thin film form on glass substrates using a rf magnetron sputtering system. The films were characterized by Scanning electron microscopy (SEM) and X-ray diffraction technique (XRD). The XRD results indicate that all the films have c-axis preferred orientation due to self-texturing mechanism. The ellipsometric spectra of the films were recorded in the photon energy range of 1 eV–5 eV. The SE spectra were analyzed with an appropriate model to accurately determine the thickness and optical constants of the ZnO:(V,Al) thin films. The profiles of refractive index and extinction coefficient with photon energy were extracted. The refractive index of the ZnO:(V,Al) film is decreased from 2.14 to 2.07 with increasing Al concentration and then is increased to 2.19 for x?=?0.04. A maximum band gap energy of ~3.57 eV was obtained for x?=?0.02. The optical band gaps of the films were found to vary from 3.57 eV to 3.41 eV, with Al content. It is evaluated that the optical constants of the ZnO:(V,Al) films can be controlled by Al content.     

Effects of substrate temperature on electrical and optical properties ITO films deposited by r.f. magnetron sputtering

Indium tin oxide (ITO) films have been prepared by r.f. magnetron sputtering using powder target. X-ray diffraction analysis indicates that the deposited films were polycrystalline and retained a cubic bixbite structure. The ITO films deposited at low substrate temperature (T _s) exhibit a (411) preferred orientation but the films deposited at high T _s prefer a (111) orientation. The substrate temperature was found to significantly affect the electrical properties. As the T _s was increased, the conductivity of ITO films was improved due to thermally induced crystallization. The lowest resistivity (8.7?×?10^?4 Ω-cm) was obtained from ITO films deposited at 450 °C. However, optical properties of the films were somewhat deteriorated. The infrared (IR) reflectance of the film increases with increasing the substrate temperature.     

Effects of the Ga-doping concentration on the characteristics of Zn<Subscript>0.7</Subscript>Mg<Subscript>0.3</Subscript>O thin films deposited by metal-organic chemical vapor deposition using an ultrasonic nebulization

Ga-doped Zn_0.7-xMg_0.3O thin films were deposited on glass substrates at 350 °C by metal-organic chemical vapor deposition using an ultrasonic nebulization technique to transport the source precursors, and the effects of the Ga-doping concentration were investigated. The films with Ga-doping concentrations less than 5 mol% grew with [001] preferred orientation perpendicular to the substrate surface and were composed of large crystallites. At Ga content greater than 5 mol%, the films grew with random orientation and very small crystallite size. The charge carrier concentration in the films increased rapidly up to 4 mol% Ga and then decreased gradually with further increases in the Ga-content. The film resistivity decreased with increasing Ga-content up to 4 mol% due mainly to the increase in charge carrier concentration. Then, the resistivity increased gradually with increasing Ga-content due to the decrease in mobility. The lowest resistivity of the Ga-doped Zn_0.7-xMg_0.3O thin film was 3.8?×?10^?1 Ωcm at the Ga doping concentration of 4 mol%. The mean transmittance in the visible range was more than 85% in all films. The optical band gap of the films increased with increasing Ga-doping concentration up to 5 mol% due to the Burstein-Moss effect.     

Growth characteristics and film properties of gallium doped zinc oxide prepared by atomic layer deposition

We carried out comprehensive studies on structural, optical, and electrical properties of gallium-doped zinc oxide (Ga:ZnO) films deposited by atomic layer deposition (ALD). The gallium(III) isopropoxide (GTIP) was used as a Ga precursor, which showed pure Ga₂O₃ thin film with high growth rate. Using this precursor, conductive Ga doped ZnO thin film can be successfully deposited. The electrical, structural and optical properties were systematically investigated as functions of the Ga doping contents and deposition temperature. The best carrier concentration and transmittance (7.2?×?10²⁰ cm^?3 and 83.5 %) with low resistivity (≈3.5?×?10^?3?Ωcm) were observed at 5 at.% Ga doping concentration deposited at 250 °C. Also, low correlation of deposition temperature with the carrier concentration and film structure was observed. This can be explained by the almost same atomic radius of Ga and Zn atom.     

Preparation of TiO<Subscript>2</Subscript> thin films deposited from highly dense targets with multi-oxide glass doping

Glass doped TiO₂ (GTO) thin films were deposited by radio frequency (RF) magnetron sputter at room temperature and annealed in a reductive atmosphere containing 90 % N₂ and 10 % H₂. Highly dense TiO₂ ceramic mixed with glass consisting of multi-metal oxides (as a sintering aid) was used as the sputtering target. This sintering aid allows low temperature densification of TiO₂ target through a liquid phase wetting mechanism, and also works as a doping resource. XRD and FESEM were carried out to characterize the microstructure of the GTO films and the results reveal that the doping of multi-metal ions enhances the crystallization and increases the grain size of TiO₂ films. TEM analysis also showed that these metal ions were dissolved into TiO₂ lattices. The electrical and optical properties of TiO₂ thin films at different glass concentrations were evaluated and compared to the films merely doped with MoO₃. The electrical resistivity of the GTO films reaches 9.1 × 10^–4 Ω·cm at 2 wt% glass doping, corresponding to a carrier density of 8.9 x 10²⁰ cm^-3 and a mobility of 7.1 cm²/Vs. Meanwhile, the electrical resistivity of the TiO₂ film doped with glass was found to be lower than that of MoO₃-doped film. This was mainly attributed to the increase in carrier concentration by double doping effect of glass. The optical band gap of the GTO films ranged from 3.34 to 3.42 eV, which is greater than that of the un-doped TiO₂ film. This blue shift of approximately 0.18 eV was due to the Burstein-Moss effect.     

Surface modification of stainless steel bipolar plates for PEMFC (proton exchange membrane fuel cell) application

Stainless steel 316 and 304 plates were deposited with a metallic film (top layer) and a conductive oxide film (intermediate layer) by a sputtering method and an E-beam method, respectively. The conductive oxide film was formed on the stainless steel plates in the range of thickness of 200, 400, and 600 nm. The XRD patterns of the conductive oxide films showed a typical indium-tin oxide (ITO) crystalline phase. The metallic films of 100 nm thickness were subsequently formed on the surface region of the bare stainless steel plates and the stainless steel plates deposited with ITO thin film. Surface morphologies of the stainless steel bipolar plates deposited with conductive film and metallic film were observed by AFM and FE-SEM. The metallic films on the stainless steel plates represented the microstructural morphology of the fine columnar grains of 10 nm diameter and 60 nm length. The electrical resistivity and contact angle of the stainless steel bipolar plates modified were examined as a function of the thickness of the conductive oxide film.     

Structural and electrical properties of Sb-doped p-type ZnO thin films fabricated by RF magnetron sputtering

We investigated the Sb-doping effects on ZnO thin film using RF (radio frequency) magnetron sputtering and RTA (rapid thermal annealing). The structural and electrical properties of the thin films were measured by X-ray diffraction, SEM (scanning electron microscope), and Hall effect measurement. Thin films were deposited at a high temperature of 800°C in order to improve the crystal quality and were annealed for a short time of only 3 min. The structural properties of undoped and Sb-doped films were considerably improved by increasing oxygen content in the Ar-O₂ gas mixture. Sb-doping also significantly decreased the electron concentration, making the films p-type. However, the crystallinity and surface roughness of the films degraded and the mobility decreased while increasing Sb-doping content, likely as a result of the formation of smaller grain size. From this study, we observed the transition to the p-type behavior at 1.5 at.% of Sb. The thin film deposited with this doping level showed a hole concentration of 4.412?×?10¹⁷ cm^?3 and thus is considered applicable to p-type ZnO thin film.     

Electrical and optical properties of fluorine-doped tin oxide (SnOx:F) thin films deposited on PET by using ECR–MOCVD

The electrical, optical, structural and chemical bonding properties of fluorine-doped tin oxide (SnO_x:F) films deposited on a plastic substrate prepared by Electron Cyclotron Resonance–Metal Organic Chemical Vapor Deposition (ECR–MOCVD) were investigated with special attention to the process parameters such as the H₂/TMT mole ratio, deposition time and amount of fluorine-doping. The four point probe method, UV visible spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic emission spectroscopy (AES), X-Ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the films. Based on our experimental results, the characteristics of the SnO_x:F thin films were significantly affected by the process parameters mentioned above. The amount of fluorine doping was found to be one of the major parameters affecting the surface resistivity, however its excess doping into SnO₂ lead to a sharp increase in the surface resistivity. The average transmittance decreased with increasing film thickness. The lowest electrical resistivity of 5.0?×?10^?3 Ω^.cm and highest optical transmittance of 90% in the visible wavelength range from 380 to700 nm were observed at an H₂/TMT mole ratio of 1.25, fluorine-doping amount of 1.3 wt.%, and deposition time of 30 min. From the XRD analysis, we found that the SnO_x:F films were oriented along the (2 1 1) plane with a tetragonal and polycrystalline structure having the lattice constants, a?=?0.4749 and c?=?0.3198 nm.     

Study of Hf—Al—O High-k Gate Dielectric Thin Films Grown on Si

Ultrathin amorphous films of Hf-aluminate (Hf—Al—O) have been deposited on p-type (100) Si substrates by pulsed-laser deposition. Transmission electron microscopy study revealed that for the films deposited in oxygen ambient with partial pressure of 1 × 10^?3 Pa, the amorphous structure of Hf—Al—O films is stable under rapid thermal annealing at temperatures up to at least 1000°C. Electrical properties have been characterized by means of high-frequency capacitance-voltage measurements at 1 MHz on the metal-oxide-semiconductor (MOS) capacitors using Pt dot electrode. The relative permittivity of the Hf—Al—O dielectric film is calculated approximately to be about 10 and the equivalent oxide thickness to SiO₂ is 30 Å. However, for the Hf—Al—O films deposited in a relatively higher vacuum condition (1 × 10^?4 Pa), islands of Hf silicide formed from interfacial reaction between the films and Si substrates. The formation of Hf silicide was attributed to the presence of Al oxide in the films that altered the Gibbs free energy for the reaction between the Hf atoms in the amorphous Hf—Al—O films and Si under an oxygen deficient condition. X-ray photoelectron spectroscope results suggested that there is Hf silicide formation in the interfacial region.     

Physical properties of transparent conducting indium doped zinc oxide thin films deposited by pulsed DC magnetron sputtering

Transparent conducting In-doped (1at.%) zinc oxide (IZO) thin films are deposited on glass substrate by bipolar pulsed DC magnetron sputtering. We have investigated the effect of pulse frequency on the physical properties of the IZO films. A highly c-axis oriented IZO thin films were grown in perpendicular to the substrate. At optimal deposition conditions, IZO films with a smoothest surface roughness of ～3.6 nm, a low-resistivity of 5.8?×?10^?3 Ωcm, and a high mobility of 14 cm/Vs were achieved. The optical spectra showed a high transmittance of above 85% in the UV–visible region and exhibited the absorption edge of near 350 nm. In micro-Raman, we observed the three phonon modes of host ZnO, which are E ₂ ^low, E ₂ ^high, and A ₁ modes, and the three additional modes. The origin of three additional modes is attributed to the host lattice defect due to the effect of In dopant and increasing the pulse frequency.     

Characterization of PT ferroelectric thin films on porous silica for pyroelectric IR detectors

Ferroelectric PbTiO₃ thin films were deposited on Pt/DS/PS/SiO₂/Si substrates by sol–gel technique. Porous silica (PS) thin film was used as thermal-insulation layer and dense silica (DS) thin film was a buffer layer to reduce surface roughness of PS layer. Root mean square surface roughness can be effectively reduced from 9.7 to 3.5 nm after PS buffer layer was prepared. The average grain size of PT thin films decreased slightly with increasing thickness of porous silica. Dielectric constant of PT increased from 107 to 171 at 1 KHz as thickness of PS layer increased from 0 to 2,000 nm. PT thin film prepared on 2,000 nm porous silica exhibited good dielectric property. The leakage current density was less than 1.6?×?10^-6 A/cm² when the applied electrical field was 200 kV/cm. The composite film is suitable for preparing pyroelectric IR detectors.     

Characterization of the CeO2 thin films for insulation layer and Pt/SrBi2Ta2O9/CeO2/Si MFISFET structure

Abstract

CeO₂ and SrBi₂Ta₂O₉ (SBT) thin films for MFISFET (metal-fcrroelectrics-insulator-semiconductor field effect transistor) were deposited by rf sputtering and pulsed laser deposition method, respectively. The effects of oxygen partial pressure during deposition for CeO₂ films were investigated. The oxygen partial pressure significantly affected the preferred orientation, grain size and electrical properties of CeO₂ films. The CeO₂ thin films with a (200) preferred orientation were deposited on Si(100) substrates at 600°C. The films deposited under the oxygen partial pressure of 50 % showed the best C-V characteristics among those under various conditions. The leakage current density of films showed order of the 10^?7～10^?8 A/cm² at 100 kV/cm. The SBT thin films on CeO₂/Si substrate showed dense microstructure of polycrystalline phase. From the C-V characteristics of MFIS structure composed of the SBT film annealed at 800°C, the memory window width was 0.9 V at ±5 V. The leakage current density of Pt/SBT/CeO₂/Si structure annealed at 800°C was 4×10^?7 A/cm² at 5 V.