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.     

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.     

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.     

Effects of sputtering pressure and thickness on properties of ZnO:Al films deposited on polymer substrates

Highly conducting and transparent aluminum doped zinc oxide (ZnO:Al) thin films have been deposited on polyimide substrate by r.f. magnetron sputtering at room temperature. The influence of sputter pressure and thickness on the structural, electrical, and optical properties of ZnO:Al films deposited on polyimide substrate is reported. The crystallinity and degree of orientation was increased by decreasing the sputter pressure. For higher sputtering pressures an increase on the resistivity was observed due to a decrease on the mobility and the carrier concentration. As the film thickness was increased, the crystallite sizes were increased, but the average transmittance in the wavelength range of the visible spectrum was decreased. The electrical performances of the ZnO:Al films deposited on glass substrates are slightly worse than the ones of the films deposited on polyimide substrates with same thickness. The lowest resistivity of 8.6?×?10^?4 Ω cm can be obtained for films deposited on glass substrate with the thickness of 800 nm.     

Low‐resistive and transparent AZO films prepared by PLD in magnetic field

Al₂O₃‐doped ZnO (AZO) thin films have been deposited onto glass substrates using a split target consisting of AZO (1 wt%) and AZO (2 wt%) by pulsed laser deposition with an ArF excimer laser (λ = 193 nm, 15 mJ, 10 Hz, 0.75 J/cm²). By applying a magnetic field perpendicular to the plume, the lowest resistivity of 8.54 × 10^?5Ω·cm and an average transmittance exceeding 91% over the visible range were obtained at a target‐to‐substrate distance of 25 mm for approximately 279‐nm‐thick AZO film (1.8 wt%) grown at a substrate temperature of 230 °C in vacuum. From cross‐sectional TEM observations and the XRD spectrum, a reason why the low resistivity (54 × 10^?5Ω·cm) was reproducibly obtained was considered to be due to the fact that a disorder of crystal growth originating in the vicinity of the interface between the substrate and the film was suppressed by application of the magnetic field and the c‐axis orientation took preference, giving rise to the increase of mobility. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(2): 40–45, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20026     

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.     

Improvement of the thermal and chemical stability of Al doped ZnO films

To improve the stability of sputter-deposited ZnO:Al (AZO) films at high temperature above 300^∘C, an amorphous Zn-Sn-O (ZTO) film was deposited on the top of AZO films as an protective layer by co-sputtering of pure ZnO and SnO₂ targets. Amorphous ZTO films had resistivity in the range from 10⁻² to 10⁻³ Ωcm and were stable up to temperature of 400^∘C. Heat treatments of bare AZO films in the atmosphere at 400^∘C resulted in a dramatic increase in the resistivity accompanied by substantial decrease in carrier concentration and Hall mobility. The AZO films covered with the ZTO film showed remarkable improvement in thermal stability for subsequent heat treatments in the temperature range from 200 to 400^∘C in the atmosphere as well as chemical stability in weak acidic solution. X-ray photoelectron spectroscopy analysis showed that the improvement was attained by ZTO layer acting as diffusion barrier of oxygens and/or water vapors.     

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.     

Preparation of hafnium oxide thin films by sol–gel method

Hafnium oxide (HfO₂) films were grown on SiO₂/Si substrates by a sol–gel method, and their crystalline structure, microstructure and electrical properties were investigated. X-ray diffraction analysis indicated that the monoclinic HfO₂ films could be obtained by annealing at 500 °C. A transmission electron microscopy (TEM) image showed that the films were grown as a spherulite grain structure with a mean grain size of approximately 15 nm. The dielectric constant of the HfO₂ films of 300 nm was approximately 21.6, and the current–voltage measurements showed that the leakage current density of the HfO₂ films was approximately 1.14?×?10^?5 A/cm² at an applied electric field of 100 kV/cm. The sol–gel method-fabricated HfO₂ films are concluded to be feasible for MEMS applications, such as capacitive-type MEMS switches.     

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.     

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.     

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.     

Structure and dielectric properties of Ca-doped (Ba0.7Sr0.3) TiO3 thin films fabricated by sol–gel method

A wide range of Ca-doped (Ba_0.7Sr_0.3)TiO₃ (BST) thin films (from 0 to 20 mol%) have been prepared on Pt/Ti/SiO₂/Si (100) substrates by sol–gel technique. The structural and dielectric properties of BST thin films were investigated as a function of Ca dopant concentration. The results showed that the microstructure and dielectric properties of the BST films were strongly dependent on the Ca contents. With the Ca dopant concentration increasing, the grain size, dielectric constant and dielectric loss of the BST thin films decreased. As the content of Ca dopant reaches 10 mol%, the dielectric constant, dielectric loss, tunability, the value of FOM and the leakage current density are 281, 0.0136, 16.7%, 12.3 and 5.5?×?10^?6 A/cm², respectively.     

Characteristics of silver powders synthesized from silver 2-ethylhexanoate and Di-n-octylamine

Uniform spherical submicron silver powders were synthesized from a long-chain alkyl carboxylate of silver 2-ethylhexanoate and an alkylamine of di-n-octylamine in this study. The decomposition of silver 2-ethylhexanoate was observed to accelerate significantly in the presence of di-n-octylamine. SEM results revealed that submicron silver powders with sizes ranging from 200 nm to 300 nm and a high tap density of 4.0 g/cm³ were successfully prepared at 150 °C for 3 h in air. TGA reveals that approximately 1.2 wt.% organic residues composed mainly of 2-ethylhexanoate with a slight amount of di-n-octylamine were attached to the silver particles, as confirmed by the FTIR and XPS results. To evaluate the feasibility for practical applications, silver paste prepared from the silver powders synthesized in this study (NAG 80 paste) was examined and characterized, and the results were compared with those of two commercially available powders (SF80 and GH67 pastes). The electrical resistivities of the NAG80 films fired at 300 and 500 °C respectively read 1.8?×?10^?5?Ω-cm and 1.1?×?10^?5?Ω-cm, both superior to those of the SF80 and GH67 films. The fine quality of the uniform submicron spherical silver powders was verified and its potential use in thick film conductors confirmed.     

Effects of rapid thermal annealing in different ambients on structural, electrical, and optical properties of ZnO thin films by sol-gel method

We studied the effects of rapid thermal annealing in different ambients on the structural, electrical and optical properties of the sol-gel derived ZnO thin films. All the films after annealing showed highly degree of (002) oriented in the X-ray diffractometry (XRD) patterns. The effects of annealing ambients on electrical properties of the films were studied. Carrier concentration, resistivity and mobility were found to be distinguished after annealed in different ambients. The sample with the lowest resistivity of 0.095 ??·cm and the largest mobility of 105.1 cm²/v·s was achieved after annealing in vacuum. XPS results indicated that more oxygen vacancies existed on the ZnO surface when annealed in vacuum than that in O₂.     

Dielectric characteristics investigation of (Ba0.7Sr0.3)(Ti0.9Zr0.1)O3 ferroelectric thin films

By the radio frequency (RF) magnetron sputtering methods, (Ba_0.7Sr_0.3)(Ti_0.9Zr_0.1)O₃ (BSTZ) ferroelectric thin films were deposited on the Pt/Ti/SiO₂/Si(100) substrates. The crystal structural and microstructure of these thin films were analyzed by means of the XRD, SEM, and AFM. Moreover, the dielectric characteristics were also investigated by the C-V and J-E analyses. The optimal deposition parameters for these BSTZ thin films were: RF power is 160 W, oxygen concentration is 25%, substrate temperature is 580°C, and chamber pressure is 0.075 mPa. Under these optimal deposition conditions, the (111) and (110) oriented polycrystalline of the BSTZ thin films grow easily. And under a bias voltage of 0.5 MV/cm, the dielectric constant and leakage current density of the BSTZ thin films are 191 and 3×10^?8 A/cm², respectively. In addition, under various measured temperatures (0 ～ 80°C) and frequencies (100 kHz ～ 1 MHz), all the dielectric constants remain almost unchanged. Compared to BSTZ thin films reported previously, in this study, the deposited thin films have the advantage of lower leakage current and hence are suitable for the applications of dynamic random access memory.     

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.     

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.     

Simulation study of an optimized current matching for In0.39Ga0.61N/In0.57Ga0.43N/In0.74Ga0.26N triple-junction solar cells

This paper deals with the design and optimization of a triple-junction (TJ) solar cell using indium gallium nitride (InGaN) material. Two tunnel diodes are used to ensure connection between the different subcells. A comprehensive study is performed by means of 2D numerical simulations to locate the best bandgap combination that leads to an optimized current matching. During the simulations, the doping concentration and the base thickness are considered as fitting parameters for the top and the middle subcells. The In_0.39Ga_0.61N/In_0.57Ga_0.43N/In_0.74Ga_0.26N bandgap combination is supposed to be 2.02 eV/1.52 eV/1.13 eV. A high short-circuit current density (13.313 mA/cm²) is achieved by assuming a base thickness of 1 µm for each subcell and a p/n doping ratio of 5?×?10¹⁸ cm^?3/5?×?10¹⁵ cm^?3 in the top cell, 1.5?×?10¹⁹ cm^?3/1.5?×?10¹⁶ cm^?3 in the middle cell, and 7.5?×?10¹⁸ cm^?3/7.5?×?10¹⁵ cm^?3 in the bottom cell. The optimized structure has an improved open-circuit voltage (2.877 V), fill factor (83%), and conversion efficiency (33.11%).