Al-doped ZnO Films Research Articles

Ultrathin Al-Doped ZnO Films Coated Li4Ti5O12 As an Anode Material with Excellent Cycling Stability and Rate Capability for Lithium-Ion Batteries

Lithium titanate oxide (Li4Ti5O12, LTO) is a lithium ion intercalated compound, which was identified as a promising anode material for LIBs with a theoretical capacity of 175 mAh g-1 within a typical potential range of 1.0 V–3.0 V. Extending the end voltage from 1.0 V to 0.01 V is an effective way to improve the electrochemical performance of LTO; the tetrahedral (8a) sites of LTO would be available for lithium ion storage to have an “extra” reversible capacity, when the end potential is lower than 0.6 V. However, this approach also leads to some other problems: (1) a lower end potential will cause a more intensive decomposition of electrolyte to form the solid electrolyte interface (SEI), which means that the initial irreversible capacity loss will increase, and (2) the change in lattice dimension during the lithium ion insertion/extraction will be increased and thus the structure stability of LTO will become worse. In this study, an Al-doped ZnO (AZO) film with various thicknesses and compositions were deposited on LTO particles by atomic layer deposition (ALD) method with different deposition temperatures and different ratios of the number of Al2O3 ALD to that of ZnO ALD. The electrochemical characterization results indicated that the coating of AZO significantly improved the electrochemical performance of LTO between 0.1 V and 3.0 V with a proper coating thickness. After 250 cycles of charge/discharge at a 1 C rate, the capacity of the optimum AZO-coated LTO sample decreased from 203 to 190 mAh g-1 with a capacity retention of ~94% at room temperature and from 224 to 216 mAh g-1 with a capacity retention of ~96% at 55 ℃. The AZO coating layer with an appropriate thickness not only increased the capacity of LTO by enhancing conductivity, but also assisted the LTO electrodes to form a beneficial interface layer to protect the LTO from the continuous attack by harmful components in the electrolyte, especially under extreme conditions, such as high temperature and high current rates.

Titanium-Based Anode Materials with Al-Doped ZnO ALD Coating for High-Performance Lithium-Ion Batteries

In commercial lithium ion batteries, graphite is used as the most common anode material, which are easy to generate lithium dendrites, when operating at a high current rate, causing an internal short circuit and thus suffering from critical safety issues. Titanium-based anode materials are a class of alternative materials to graphite, which has a potential to offer a significant safety advantage over the graphite anode. Lithium titanate oxide (Li4Ti5O12, LTO) and titanium dioxide (TiO2) are two of the most studied titanium-based anodes because of their properties of intrinsic safety and small volume expansion. Recently our group deposited high electronic conductive Al-doped ZnO (AZO) films on the LTO and anatase TiO2 samples by atomic layer deposition (ALD). The optimum AZO-coated LTO exhibited a superior rate capability and cycling stability at 55 ℃ within a potential rage of 0.1 V to 3.0 V; the optimum AZO-coated TiO2 delivered a much higher capacity than that of the uncoated TiO2 even after 500 cycles of discharge/charge at 1 C rate (1 C = 168 mAh g-1). The coating of AZO thin films is believed to improve the conductivity of the active materials, protect the active materials from the electrolyte, and suppress the undesirable interfacial reactions between them.

Texture and phase control of magnetron-sputtered VO2 thin films with an Al-doped ZnO seed layer using topotactic oxidization

We developed a technique to produce stoichiometric VO2 films with a well-defined (010) orientation, using an Al-doped ZnO (AZO) thin film and topotactic oxidation. The AZO seed layer was prepared on a glass substrate by radio frequency magnetron sputtering (RF-MS), and then the V2O3 film was deposited on the AZO film by RF-MS. Finally, the V2O3 film was post-annealed, and underwent topotactic oxidation in air to convert the V2O3 phase to the VO2 phase. The AZO seed layer converted V2O3 to VO2 while maintaining the crystallographic orientation. Consequently, well-defined (010) orientated 200-nm-thick VO2 films with large change in electrical resistivity of 1.55 × 103 times together with large change in optical transmittance of 64.3% at wavelength of 2000 nm, before and after the transition, were successfully obtained by combination with AZO seed layer and topotactic oxidation.

Performance optimization of transparent and conductive Zn1-xAlxO thin films for opto-electronic devices: An experimental & first-principles investigation

In the present work, a combination of the experimental techniques with first principle density functional theory (DFT) based calculations has been employed to study the performance of the aluminum doped ZnO (AZO) thin films as transparent conducting oxide (TCO) material. The AZO thin films with varying doping concentration (0 wt% to 10 wt%) and having thickness (<100 nm) were deposited on silicon substrate using pulsed laser deposition. Various structural, optical and electrical properties of the films have been explored using a variety of the experimental techniques e.g. X-ray diffraction, X-ray reflectivity, scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy and current-voltage characteristic measurements. The different physical properties are observed following interesting trends where the characteristics property shows an optimum response at a particular doping concentration (5 wt%). These trends are correlated and explained based on the structural evolution in the nanostructured AZO thin films on varying doping concentration. Moreover, the prepared films are found to be having significantly high transmission and low resistivity making them useful for TCO application. The experimental findings for the Al-doped ZnO are supported by DFT calculations. Overall, our study provides important inputs to control the properties of Al doped ZnO films for their applications in optoelectronic devices.

Quantum dot light-emitting diodes with an Al-doped ZnO anode

A study of hybrid ZnCdSeS/ZnS quantum dot light-emitting diodes (QLEDs) device fabricated with indium tin oxide-free transparent electrodes is presented. Al-doped zinc oxide (AZO) prepared by magnetron sputtering is adopted in anode transparent electrodes for green QLEDs with different sputtering pressures. A Kelvin probe force microscopy measurement showed that AZO has a work function of approximately 5.0 eV. The AZO/poly(ethylene-dioxythiophene)/polystyrenesulfonate (PEDOT:PSS) interface can be adjusted by the sputtering pressures, which was confirmed by hole-only devices. AZO films with low surface roughness can form a good AZO/PEDOT:PSS interface, which can increase the holes’ injection, and result in an improved charge balance. The maximum current efficiency, luminance, and external quantum efficiency of the optimized QLED devices under a sputtering pressure of 1 mTorr can achieve values of 50.75 cd A−1, 102 500 cd m−2, and 12.94%, respectively.

Development of ALD ZnO:Al as transparent conductive films

We report the deposition of ultrathin Al-doped ZnO (AZO) films by using atomic layer deposition (ALD) and results from X-ray photoelectron spectroscopy (XPS) and photoelectrical measurements. The AZO films were deposited on glass, silicon and polyethylene terephthalate (PET) substrates and their structural and photoelectrical properties were measured and discussed. Based on the results, selected AZO films deposited on PAT were implemented as transparent electrodes in a polymer dispersed liquid crystal display device (PDLC). The electro-optical modulation characteristics of these devices are comparable to those of devices using commercial ITO electrodes.

New Approach for Fabricating of Deep Submicron Free-Standing Polyimide Thin Film

A new approach for manufacturing ultrathin free-standing polyimide film was proposed. This approach involves casting polyamic acid solution to a Al-doped zinc oxide film coated substrate sputtered at room temperature and to form polyamic acid film. The polyamic acid film was released from substrate in 0.5% diluted hydrochloric acid. Then polyamic acid was reattached to glass substrate and was transformed into polyimide film by thermal imidization with gradient heat treatment process. After that, thickness of the1000 nm polyimide film was reduced by KrF excimer laser ablation with 100 pulses at 45 mJ/cm2 and 30 pulses at 75 mJ/cm2, and 200 nm free-standing polyimide film was obtained. By this method, free-standing polyimide films of 1000 nm and 200 nm thickness were fabricated without and with excimer laser ablation reduction, respectively.

Damp-heat durability comparison of Al-doped ZnO transparent electrodes deposited at low temperatures on glass and PI-tape/PC substrates

Durability performances are compared for Al-doped ZnO (AZO) transparent electrodes deposited on hard slide-glass and flexible polyimide-tape attached to polycarbonate (PI-tape/PC) substrates. To identify the appropriate sputtering configuration, the AZO thin films are first deposited on the glass substrates via reactive RF-magnetron sputtering under 90 sccm of argon gas and 3 sccm of oxygen gas at room temperature (RT) with 83 to 90 W of RF power for 30 min. When deposited, only the sputtering configuration with 85 W of RF power could produce the AZO films with acceptable optoelectrical properties for transparent electrodes: 80% average visual transparency and 10 Ω/□ at the thickness of 1.1 μm. The temperature at the surface of the substrates rises from RT to 88 °C due to the sputtering with 85W of RF power for 30 min, and this configuration is successfully conducted for AZO film depositions on both the glass and PI-tape/PC substrates. After exposure to a damp-heat (DH) test at 85 °C and 85% relative humidity (RH) for 25 days, the conductivity of the AZO films on the PI-tape/PC substrates is significantly degraded: many cracks are visible on the films, significantly decreasing the Hall mobility. Conversely, the films deposited on the glass substrates exhibit durable high conductivity, no cracks, and excellent stability of the Hall mobility. Despite this significant difference in Hall mobility evolution, the films on both substrates show similar patterns of a slight decrease in carrier concentrations, suggesting that chemical characteristics, extensively reported as the key for the DH degradation of AZO films, are less involved in this durability study featuring AZO films prepared via a low oxygen-to-argon gas ratio of reactive sputtering at low temperatures.

Enhanced luminescent performance with surface wrinkled Al-doped ZnO films

To improve the photoluminescence (PL) properties of ZnO films, researchers generally preferred cations doping such as Al, but the effects of Al doping on the increase in PL intensity of ZnO films were dissatisfactory usually when surface of films was smooth. In this work, a new and simple process was proposed for enhancing the PL intensity in the range of 375–600 nm of ZnO films. We prepared surface wrinkled Al-doped ZnO (AZO) films by sol–gel method with a quickly pre-annealing process. The wrinkle morphology was found to provide a larger absorption and luminescence area. Results showed that the wrinkle surface as compared with the smooth surface could raise the PL intensity of AZO films to 4 times, which made ZnO further close to the application for ultraviolet and visible luminescent devices.

Al-Doped ZnO Transparent Conducting Glass With an IGZO Buffer Layer for Dye-Sensitized Solar Cells

In this article, we employ the Al-doped ZnO (AZO) film as the transparent conductive oxide (TCO) onto the glass substrate for dye-sensitized solar cells (DSSCs). To improve the electrical property of AZO, a film of indium gallium zinc oxide (IGZO) is introduced as the buffer layer between the AZO and glass substrate. Experimental results show that the resistivity of the AZO glass is reduced with the introduction of the IGZO buffer layer, and the photovoltaic efficiency is enhanced when the AZO/IGZO TCO is used in DSSC. In addition, it is found that the photovoltaic efficiency of the DSSC with AZO/IGZO glass is also higher than those of the DSSCs with conventional fluorine-doped tin oxide (FTO) and indium-doped tin oxide (ITO) glasses. Therefore, the composite AZO/IGZO film is promising to replace the FTO and ITO films for DSSCs.

Improvement of characteristics of flexible Al-doped ZnO/Ag/Al-doped ZnO transparent conductive film using silver

In recent years, transparent conductive oxide (TCO) films that can be applied to flexible devices have attracted considerable attention. Among TCOs, indium tin oxide (ITO) is frequently used, but ITO contains the rare metal In and is inflexible. Therefore, the authors focused on an Al-doped ZnO (AZO) transparent conductive film as an alternative material for ITO. The authors prepared films on polyethylene naphthalate (PEN) substrates to prepare flexible electrodes. PEN substrates are sensitive to heat and must be deposited at low temperatures. However, there is a limit to improving the conductivity of AZO film formation at low temperatures. Therefore, the authors focused on the AZO/Ag/AZO multilayer transparent conductive films. The AZO layer was deposited by RF magnetron sputtering, and the Ag layer was deposited by electron beam evaporation. The electrical and optical characteristics were evaluated by changing the deposition conditions during the AZO and Ag deposition. Thus, when the thickness of the Ag layer was changed, the maximum transmittance was obtained at a thickness of 10 nm. Next, the upper AZO film was divided into room temperature/50 °C. When the upper AZO is formed at 50 °C, the already deposited Ag is affected by thermal oxidation. Ag was protected from thermal oxidation by first depositing the upper AZO at room temperature and then applying 50 °C, resulting in improved transmittance and resistivity. Furthermore, the resistivity and transmittance were improved by increasing the deposition rate of the Ag layer due to a decrease in the oxygen content in the Ag layer. Among the formed thin films, the best obtained characteristics were the resistivity of 1.24 × 10−4 Ω cm and the transmittance of 84.8%.

Influence of unintentionally incorporated Ar atoms on the crystalline polarity of magnetron-sputtered Al-doped ZnO polycrystalline films on glass and sapphire substrates

The authors investigated the relationship between the content of incorporated Ar atoms and the crystalline polarity of polycrystalline Al-doped ZnO (AZO) films and examined the influence of this relationship on the resulting growth rate, crystallographic texture, and electrical properties. They deposited AZO films on glass and c-plane sapphire substrates via radio-frequency magnetron sputtering at substrate temperatures (Ts) of 100 or 200 °C using sintered AZO targets with an Al2O3 content of 2.0 wt. %. The incorporation of a large amount of Ar atoms induced a change in the crystalline polarity from Zn-polar to O-polar, the latter of which is associated with numerous obstacles, such as a lower deposition rate, large residual compressive stress, and increased electrical resistivity. The authors demonstrated that increasing the Ts led to a reduction in the amount of unintentionally retained Ar atoms, thereby affording Zn-polar AZO films with their associated advantages.

Influence of Al doping on the crystal structure, optical properties, and photodetecting performance of ZnO film

The structural, optical, and electrical properties of undoped and Al-doped ZnO films deposited on p-Si (001) substrate were studied using DC-unbalanced magnetron sputtering. This study is motivated by the absence of detail reports concerning the orbital states inducing the optical bandgap (Eg) blueshift. Besides, the influences of Al on the possible modification of point defect and the photodetecting performance are highlighted to offer guidelines for better development in ZnO-based photodetector. It was found that the Al doping reduced the grain size. The doping increased the lattice parameters and slightly decreased the local-symmetry distortion at ZnO4. From the absorbance spectra, the doping increased Eg of ZnO film (3.28–3.36 eV), induced by the Burstein-Moss effect. From the density-functional calculation, the Burstein-Moss effect induced Eg from the valence band maximum (VBM) to Fermi level located above the lowest Zn 4s conduction state. From the photoluminescence spectra, the undoped film showed the transitions from O vacancy, Zn interstitial, and free-exciton states to the VBM. The doped film showed the transitions from Zn interstitial to O interstitial and few Zn vacancy states at the cost of O vacancies. Moreover, the energy level of free-exciton states slightly decreased. Notably, O interstitials increased the lattice parameters. From the electrical properties, the doping enhanced the ultraviolet-region photo-to-dark-current ratio up to 3.044 V, leading to the photodetecting sensitivity enhancement. This study emphasizes the significant effect of Al doping on the optical absorbance, point-defect evolution, and photodetecting performance of ZnO film for low-voltage ultraviolet photodetector applications.

Effects of AZO film as inductive layer and annealing temperature on microstructure crystallinity and electrical and optical properties of IGZO/SiO2 and IGZO/AZO/SiO2 specimens

In the present study, annealing at three temperatures (800, 900, and 1000 °C) is applied to indium gallium zinc oxide (IGZO)/SiO2 specimens to investigate the effect of annealing temperature on amorphous IGZO (a-IGZO) crystallization. Then, IGZO/AZO/SiO2 specimens are prepared and annealed at 1000 °C to evaluate the effect of an Al-doped ZnO (AZO) film inserted between IGZO and an a-SiO2 substrate on a-IGZO crystallization to IGZO. The effects of annealing temperature and the AZO film on microstructure crystallization and optical and electrical properties are evaluated. The intensity of the X-ray diffraction peaks of crystalline IGZO increased with increasing annealing temperature. The insertion of the AZO film induced a-IGZO crystallization, which led to comparatively higher peak intensities for the IGZO/AZO/SiO2 specimen annealed at 1000 °C. The use of AZO film changed the In3+ hexagonal structure of the IGZO/SiO2 specimen with unequal bond lengths into the regular hexagonal structure of the IGZO/AZO/SiO2 specimens. Increasing the annealing temperature from 800 to 1000 °C slightly reduced (~0.09%) the transmittance of the IGZO/SiO2 specimens. The microstructure transformation due to AZO addition made the transmittance of the IGZO/AZO/SiO2 specimen annealed at 1000 °C only 1.46% lower than that of the IGZO/SiO2 specimen. A sufficiently high annealing temperature and/or the use of AZO film increases carrier concentration and mobility and decreases resistivity and band gap. AZO film can be used to induce the crystallization of a-IGZO to efficiently improve electrical properties without a significant loss in transmittance.

Effect of the Si doping on the properties of AZO/SiC/Si heterojunctions grown by low temperature pulsed laser deposition

The structural and photoelectrical properties of Al-doped ZnO (AZO)/SiC/p-Si and AZO/SiC/n-Si heterojunctions, fabricated at low temperature by pulsed laser deposition, were investigated by means of a number of techniques. Raman analysis indicates that SiC layers have the cubic 3C-SiC phase, whilst X-ray diffraction measurements show that AZO films exhibit a hexagonal wurtzite structure, highly textured along the c-axis, with average crystallites size of 35.1 nm and lattice parameter c of 0.518 nm. The homogeneous and dense surface morphology observed by scanning electron microscopy was confirmed by atomic force microscopy images. Moreover, UV–Vis-NIR spectra indicated a high transmittance of SiC films in the region 550–2500 nm, about 80% transmittance of AZO films in the 450–1000 nm region, and optical band gaps in good agreement with literature. These results prove that pulsed laser deposition is a low-cost technique suitable to grow SiC and AZO films with excellent material properties. The effect of the Si doping on the current transport mechanisms in the heterojunctions was investigated by current-voltage measurements under dark and white light illumination. Both heterojunctions exhibit a diode behaviour and relatively low leakage current, with a noticeable superiority for the AZO/SiC/n-Si device also under illumination, with an illumination/dark ratio of about 400. Our results indicate that the AZO/SiC/p-Si heterojunctions, with higher values of ideality factor, series resistance and lower rectifying ratio, have a complex current transport compared to the diodes grown on n-type Si. Additionally, capacitance-voltage measurements and Mott-Schottky plot allowed to determine a built-in potential of 0.51 V for the Al/AZO/SiC/p-Si/Al device.

Insight of the doping mechanism of F and Al co-doped ZnO transparent conductive films

Transparent conductive oxide (TCO) films, as transparent electrodes, are widely used in thin-film solar cells. The performance of TCO film has a significant influence on the conversion efficiency of the film solar cell fabricated byusing it. Although the conductivity can be improved by increasing the carrier concentration, the transmittance in the long wave will be sacrificed. Therefore, the only feasible method is to increase the carrier mobility within a certain carrier concentration range, rather than increase the mobility by reducing carrier concentration. In this paper, the F and Al co-doped ZnO (FAZO) films are deposited on glass substrates (Corning XG) by an RF magnetron sputtering technique with using a small amount of ZnF&lt;sub&gt;2&lt;/sub&gt; (1 wt.%) and Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; (1 wt.%) dopant. The influences of sputtering pressure on the structure, morphology and photoelectric characteristics of the films are respectively investigated by X-ray diffraction analysis, scanning electron microscope, Hall effect measurement, and ultraviolet–visible–near infrared spectrophotometry. All the thin films show typical wurtzite structure with the &lt;i&gt;c&lt;/i&gt; axis preferentially oriented perpendicular to the substrate. With the increase of sputtering pressure, the deposition rate of FAZO film decreases, the crystallization quality is deteriorated, surface topography changes gradually from “crater-like” to co-existent “crater-like” and “granular-like”, and the surface roughness increases. The FAZO film deposited at 0.5 Pa presents the optimal performance with a mobility of 40.03 cm&lt;sup&gt;2&lt;/sup&gt;/V·s, carrier concentration of 3.92 × 10&lt;sup&gt;20&lt;/sup&gt; cm&lt;sup&gt;–3&lt;/sup&gt;, resistivity of 3.98 × 10&lt;sup&gt;–4&lt;/sup&gt; Ω·cm, and about 90% average transmittance in a range of 380－1200 nm. The theoretical result shows that the co-doping of F and Al takes the advantages of single F and Al doped ZnO films, and overcomes the shortcoming of metal elements doping, which donates the carriers just from doped metal elements. Furthermore, the co-doping of F and Al not only increases the carriers but also reduces the scatterings caused by the inter-orbital interaction of doped atoms. The doped F 2p electron orbitals repel the O 2p and Zn 4s electron orbitals, making them move down and donate electrons. At the same time, the orbitals of Al 3s and Al 3p also make a contribution to the conductivity. After co-doping of F and Al, both the carrier concentration and conductivity increase significantly.

Structural and optical properties of Al-doped ZnO thin films produced by magnetron sputtering

Experimental and theoretical investigations of the structure and optical properties of Al-doped ZnO (AZO) thin films produced by magnetron sputtering under different values of electric current were conducted. The XRD results confirm the formation of the AZO thin films with hexagonal wurtzite structure, with preferential orientation along the crystallographic plane (002), direction c. The increment of electric current allowed an increase in average crystallite size. The FE-SEM and AFM images analyses of the AZO films revealed the occurrence of nucleation on the substrate surface that formed films with granular and rough structure. The higher substrate temperature caused by the higher value of electric current had influence on the grain size and thickness (ranging from 974 to 1500 nm) of the formed thin films. Due to the high absorption of free carriers, the optical transmittance of the AZO films was acceptable for the visible spectrum and limited to the near infrared region. The energy band gap values for both AZO films, measured from the optical transmission spectra, were ideal for semiconductor applications. The ab initio calculations using DFT and the method LSDA + U along with the correction of Hubbard were successfully applied to investigate the structural and optical effects. The band structures of the pure ZnO and ZnO:Al, calculated in this work, presented Eg values close to the experimental results. Therefore, these results imply that our methods are reliable and that the calculations are in accordance with the experimental results.

Effects of pressure and substrate temperature on the growth of Al-doped ZnO films by pulsed laser deposition

Al-doped ZnO (AZO) thin films were deposited on p-Si (100) by pulsed laser deposition from a composite ceramic target (ZnO:Al2O3) by using 355 nm laser at different O2 background pressure and substrate temperature. Upon ablation at laser fluence of 2 Jcm−2, plasma plume consists of Zn neutrals and ions, Al neutrals and O neutral are formed. As the O2 background pressure increases from 3 Pa to 26 Pa, the energy of the plasma species are moderated. The results show that the ions density and velocity reduced significantly above 13 Pa. The velocity of the ions reduced from 14 kms−1 to 11 kms−1 at 13 Pa, while the ions energy reduced from 63 eV to 42 eV respectively. Below 13 Pa, crystalline and homogeneous AZO nanostructured films were formed. Above 13 Pa, the process results in low crystallinity films with higher porosity. The resistivity of the films also increases from 0.1 ohmcm to 24 ohmcm as the pressure increased. At fixed O2 background pressure of 3 Pa, the adatom mobility of atoms on the substrates is altered by substrate heating. The resistivity of the films decreased to 10–3 ohmcm when the substrates are heated to 100 °C–300 °C during deposition. The films with highest carrier density of 1020 cm−3 and carrier mobility of 13 cmV−1 s−1 are achieved at 200 °C.

Role of the Interface between Ag and ZnO in the Electric Conductivity of Ag Nanoparticle-Embedded ZnO.

The addition of Ag nanoparticles (Ag NPs) with an average size of 30 nm into ZnO increases the electric conductivity up to 1000 times. While a similar increase in the conductivity is observed in a mixture of Ag nanoparticles and Al-doped ZnO (AZO) films, a physical mechanism underlying the change in electric conductivity is not the same for Ag NP-added ZnO and Ag NP-added AZO. In Ag NP-added ZnO, an ohmic junction is formed at the ZnO-Ag interface, and electrons are accumulated in ZnO near the ZnO-Ag interface until electron-rich islands are connected. However, in Ag NP-added AZO, electrons in Ag NPs move to the AZO matrix via thermionic emission and travel through the AZO matrix. This change in electron transport at ZnO-Ag and AZO-Ag interfaces is due to the fact that the work function of ZnO (4.62 eV) is larger than those of Ag (4.24 eV) and AZO (4.15 eV). An increase in Ag NP content in the ZnO matrix leads to the overlap of the electron accumulation regions and forms a percolation path for the electron transport without deteriorating the electron mobility. Hence, the electron concentration increases to 2.4 × 1020/cm3 in the 1.4 vol % Ag NP-added ZnO film. In addition, Ag NPs have a negligible effect on the transmittance, and the best Haacke figure of merit (ΦH) values are 2.86 and 5.18 for ZnO:Ag NP and AZO:Ag NP, respectively.

Al-doped ZnO transparent conducting oxide with appealing electro-optical properties – Realization of indium free transparent conductors from sputtering targets with varying dopant concentrations

The objective of this work is to provide high quality indium free transparent and conducting oxide film in which ZnO is the primary component and Al is the only dopant. A range of Al-doped ZnO (AZO) transparent conductors has been realized from the developed AZO sputtering targets with varying dopant concentrations with content of the dopant material Al2O3 added in the range 0.5–5.0 wt.%. X-ray diffraction, Raman spectroscopy, AFM measurements, and elemental analyses reveal promising material properties. The sheet resistance of 2.3 Ω/sq, visible light transmittance over 90 %, and figure of merit of 75.9 mΩ–1 are the optimal electro-optical characteristics of AZO thin films. The resistivity of AZO films is dependent on the dopant concentrations with the lowest value estimated to be 1.66 × 10–4 Ω cm. A comparison of the figure of merit of AZO films with that of ITO suggests application potential of AZO as transparent conducting oxide. High transparency effect of AZO films in the near-UV spectral region is limited by the strong fundamental absorption. The hypsochromic shift of this onset of band-to-band absorption accentuates beyond 1.0 wt.% of Al2O3, which is primarily ascribed to the Moss-Burstein effect in this degenerate semiconductor. The bulk plasmon frequencies fall in the near infrared region where transmittance curves of AZO films completely differ from that of ZnO. A significantly high free carrier absorption in the near infrared suggests formation of free electron gas upon doping. With abundance of free electrons and low dielectric loss, AZO may serve as a promising infrared plasmonic material.