Al:ZnO Thin Films Research Articles

Effects of 300 keV N+ Ion Irradiation on Radio-Frequency Sputtered Al-ZnO Thin Films for a Low Energy Regime

The experimentally observed effects induced by ion irradiation in AZO thin films are discussed in limited articles. Here, in the present study, we report the results of ion irradiation by 300 keV Nitrogen ions. To study the structural, morphological, and optical properties of thin film, XRD, FE-SEM, and UV visible spectroscopy were used and it was confirmed by the structural investigation that the ion irradiation resulted in changes in different calculated structural parameters. Furthermore, different dopant concentrations are examined in relation to the effects of irradiation. The polar crystal growth orientation mechanism is initiated over nonpolar crystal growth orientation, as the 2%AZO thin films are presented to ion beam irradiation. The transition in the stress of thin film after N ion irradiation is also discussed. The phenomena responsible for the morphological changes is discussed. The observed morphological changes are correlated with structural changes. The change in the colour of the thin films after irradiation is explained. The other alterations in the thin films’ optical properties are also discussed. The systematics study of the irradiated thin films may be helpful for device fabrication.

A structural, optical and electrical comparison between physical vapour deposition and slot-die deposition of Al:ZnO (AZO)

Aluminium-doped zinc oxide (AZO) is a potential low-cost alternative to indium tin oxide (ITO) for application in optoelectronic devices as a transparent conducting thin film. Typically, AZO thin films are deposited using expensive, high vacuum equipment with high energy cost and materials wastage. In this study, slot-die coating was used as an inexpensive alternative to vacuum deposition to form AZO nanoparticle thin films under ambient laboratory conditions. The films were characterised structurally, optically and electrically and compared with a commercially obtained AZO film fabricated using physical vapour deposition (PVD). Structural characterisation of the nanoparticle film shows uniform coverage across the substrate with increased crystal quality following annealing in Ar up to 500 ^{circ }C. The optical properties of the nanoparticle film exhibit a wider band gap than the PVD film, while the high density of grain boundary defects between the nanoparticles inhibits sheet conductivity.Graphical abstract

P‐1.12: Vacuum Annealing Treatment on High‐Performance AlZnO Thin Film Transistors

We explore the effects of vacuum annealing temperature (100, 200, and 300 °C) on device performance of AlZnO thin film transistors (AZO TFTs). The AZO TFTs show excellent electrical properties at annealing temperature of 100 °C, including a saturation mobility of 12.2 cm2V−1s−1, a sub-threshold swing of 186 mV/decade, and an on/off ratio state current ratio over 108. Our findings promote practical application of the AZO TFTs to advanced displays.

Study on piezo-phototronic effect of AlZnO thin film flexible ultraviolet photodetector

In this research, AlZnO (AZO) flexible ultraviolet (UV) photodetectors (PDs) with piezo-phototronic effect were fabricated by radio frequency (RF) magnetron sputtering. AZO has the advantages of low-cost synthesis and relatively high light response in the UV region. By changing the thickness of the AZO film, the carrier density obtained in the AZO film is adjusted. In the AZO film with lower carrier density, piezoelectric polarization charges (piezo-charges) are easily exposed. Under the action of the piezo-phototronic effect, the photocurrent and responsivity of the two groups of AZO thin film PDs with growth times of 10 min and 20 min increased, and the maximum response increased by 286% and 143%, respectively. This broadens the application range of ZnO-based composite materials.

Spatial profile of Al-ZnO thin film on polycarbonate deposited by ring-shaped magnetized rf plasma sputtering with two facing cylindrical Al2O3 – ZnO targets

Radial profiles of the ion saturation current are measured in a ring-shaped magnetized radio-frequency plasma sputtering process with two facing cylindrical ZnO targets including Al2O3 (2% wt.). The profile has a non-uniform shape with a peak whose position corresponds to the target near the electrode due to the effect of the magnetic field distribution. It becomes uniform at large distances between the substrate and a target (d st ≥ 50 mm). The radial profile of the resistivity of the Al-ZnO (AZO) films deposited on a polycarbonate plate at Ar gas pressure of 0.27 Pa is uniform at about 10−3 Ω · cm for d st ≥ 50 mm. The films deposited at various positions and room-substrate-temperature also show a good crystallinity based on an X-ray diffraction peak of about 33.95–34.44°. The grains exhibit a preferential orientation along the [002] axis with its size ranging from 18.15 to 28.17 nm. A higher transmittance of 95.6% in the visible region is also obtained.

Influence of aluminum precursor nature on the properties of AZO thin films and its potential application as oxygen sensor

Al:ZnO (AZO) thin films were successfully deposited on pre-heated glass substrate using organic and inorganic aluminum precursors, i.e. aluminum acetylacetonate (ac) and aluminum chloride hexa-hydrate (cl), respectively. The properties of spray pyrolysis grown AZO thin films were investigated for a wide range of Al/Zn ratio (0.2–10%) before and after annealing at 320 °C in an inert nitrogen atmosphere. There was remarkable improvement in the electrical properties of the films after annealing. The electrical conductivity also improved on doping but the magnitude of improvement on using cl was 10 times more as compared to ac. Photoluminescence spectroscopy of AZO thin films revealed that the near band edge emission (NBE) remarkably improved on increasing Al/Zn ratio using cl with concomitant reduction in blue luminesce (BL) intensity in the visible region. On using ac, the BL intensity however increased while NBE emission decreased. AZO thin films possessed more than 85% average optical transmission in the visible region. Blue shift in the optical band gap was observed using both types of Al precursors. cl based Al precursor produces pyramid like structure at higher Al/Zn ratios. X-ray diffraction studies revealed that AZO thin films possess hexagonal wurtizite structure with preferred orientation along c-axis. The value of the crystallite size decreased on increase in Al/Zn ratio for both types of precursors. These thin films possess good oxygen gas sensing ability and have potential ability to be used as oxygen sensor.

The optical and electrophysical properties of Al-ZnO thin films

Nanocrystalline films of pure ZnO and Al-ZnO with a molar ratio Al:Zn = 1:99 and 3:97 were obtained by solid-phase pyrolysis. By XRD analysis the films have a wurtzite structure, the size of the crystallites is about 21 nm. The obtained films are almost transparent in the near UV range (the absorption coefficient is less than 16 %) and are transparent in the visible wavelength range. Electrophysical measurements have shown that the addition of minor amounts of aluminum to the ZnO film leads to a decrease in electrical conductivity by 2–3 orders of magnitude and the activation energy of electrical conductivity. The film with a molar ratio Al:Zn = 1:99 has the lowest activation energy of conductivity (0.23 eV).

Thin and flexible transparent conductors with superior bendability having Al-doped ZnO layers with embedded Ag nanoparticles prepared by magnetron sputtering

In this work, an attempt has been made to develop thin and flexible transparent conductors based on the interfaces of Ag nanoparticles (AgNP) and Al:ZnO (AZO) deposited by sequential magnetron sputtering. The entire deposition process is completed within 20–28 min without breaking vacuum thereby preventing post-deposition oxidation of Ag NPs. The co-existence of high transmittance and low sheet resistance along with stability under mechanical bending is a bit difficult to achieve in bare AZO thin film having thickness below 200 nm. The resistivity of the optimized AZO/AgNP/AZO composite structure is significantly low at 3.3 × 10−5 Ω cm, which is two orders lower than that of AZO thin film of similar thickness. The figure of merit of the optimized composite structure peaks at 39.0 mΩ−1 corresponding to Ag NPs growth period of 5 min. The novel fabrication of AZO/AgNP interface in a dry and vacuum environment facilitates superior bending stability required for a flexible transparent conductor. The findings suggest that a system of two thin layers of AZO with embedded Ag NPs can be a potential candidate as an indium free transparent conductor for the next generation optoelectronic device.

Preparation and Characterization of Sol–Gel Dip Coated Al: ZnO (AZO) Thin Film for Opto-Electronic Application

Aluminum doped zinc oxide (AZO) thin film was prepared by sol–gel dip coating method from methanol and monoethanolamine respectively, used as solvent and stabilizer agent. From the XRD study, it was confirmed that the aluminum was incorporated into the ZnO lattice. The prepared film have polycrystalline in nature and the film exhibit hexagonal wurtzite structure with (002) direction. SEM and AFM studies showed well defined smooth and uniformed wrinkle shaped grains distributed regularly on to the entire glass substrate without any pinholes and cracks. From the optical study, the observed highest transmittance was about 82% in the visible range and the band gap is 3.15 eV. Room temperature PL spectra exhibited a strong UV emission peak located at 390 nm for the deposited film. The electrical properties of the AZO thin film was studied by Hall-Effect measurement and found that it has n-type conductivity with low resistivity (ρ) of about 9.06 × 10–3 Ω cm.

AZO (Al:ZnO) thin films with high figure of merit as stable indium free transparent conducting oxide

This work presents a broad study of transparent and conducting Al-doped ZnO (AZO) thin films that could replace indium tin oxide (ITO) as transparent electrode in optoelectronic devices. AZO thin films are deposited by pulsed DC magnetron sputtering at a sputtering power of 80 W with different pulse frequencies in the range 50–100 kHz. Diffraction data confirm formation of doped ZnO and AZO thin films exhibit preferred orientation in the c-direction. The crystallite sizes of Al:ZnO are in the range 16–21 nm. The field emission scanning electron microscopy and atomic force microscopy of AZO thin films reveal nucleation and growth of uniform and dense films with better quality films deposited at a pulse frequency 75 kHz. A simple and non-destructive optical method is adopted to determine thickness and dispersion parameters such as dispersion energy, carrier concentration to effective mass ratio, and plasma frequency. AZO thin films offer excellent visible light transparency and limited transparency in the near-infrared region due to free carrier absorption. The sheet resistance of AZO thin films is recorded in the range 9–45 Ω/sq making these transparent conducting oxides (TCOs) suitable for optoelectronic applications. The figure of merit as high as 1.99 × 10−2 Ω−1 is achieved for AZO thin film deposited at a pulse frequency of 75 kHz. AZO thin film sputtered with a pulse frequency of 75 kHz is quite stable in ambient oxidizing environment and surface adsorption sites might govern the initial oxidation of films when exposed to atmosphere. Excellent figure of merit and good stability of sputtered AZO thin films as TCO fulfill the requirements of a transparent electrode in photovoltaics.

Preparation and Characterization of Sol-Gel Dip Coated Al: ZnO (AZO) Thin Film for Opto-electronic Application

AbstractAluminum doped zinc oxide (AZO) thin film was prepared by sol–gel dip coating method from methanol and monoethanolamine respectively, used as solvent and stabilizer agent. From the XRD study, it was confirmed that the aluminum was incorporated into the ZnO lattice. The prepared film have polycrystalline in nature and the film exhibit hexagonal wurtzite structure with (002) direction. SEM and AFM studies showed well defined smooth and uniformed wrinkle shaped grains distributed regularly on to the entire glass substrate without any pinholes and cracks. From the optical study, the observed highest transmittance was about 82% in the visible range and the band gap is 3.15 eV. Room temperature PL spectra exhibited a strong UV emission peak located at 390 nm for the deposited film. The electrical properties of the AZO thin film was studied by Hall-Effect measurement and found that it has n-type conductivity with low resistivity (ρ) of about 9.06 × 10^–3 Ω cm.

Transparent conducting Al:ZnO thin films on large area by efficient cylindrical rotating DC magnetron sputtering

Al: ZnO (AZO) thin film provides non-toxic, cost effective visible light transparent conductive front contact for various photonic and electronic applications. Development of AZO thin films on large area soda lime glass substrates using direct current magnetron sputter coater with cylindrical rotating ceramic targets is investigated and is presented in this work. Design of experiments and Investigation on detailed structural, electrical, optical characterization was carried out to fine tuning of various sputter process parameters such as sputtering power, pressure and substrate temperature to obtain uniform electrical conductivity and transmittance over a large area. The best resistivity of 4.07 × 10−4 Ω cm and transmittance of 84% with thickness uniformity better than 97% on 300 mm × 300 mm area glass substrate was achieved on the AZO thin films sputtered using optimized process conditions.

Transparent and flexible heaters based on Al:ZnO degenerate semiconductor

We report on high performance transparent Al:ZnO (AZO) thin film heaters on flexible polymer (polyethylene terephthalate) and glass substrates which demonstrate low sheet resistivity. AZO thin films were grown by radio-frequency magnetron sputtering at low Ts (below 200 °C) on flexible, transparent polyethylene terephthalate substrates that show stable and reproducible results by applying low (<10 V) voltages. This study also examined identical AZO thin films on glass substrates that showed highly reproducible heating effects due to the Joule heating effect. The potential applications are foldable and wearable electronics, pain/injury therapy smart windows, automobile window defrosters, and low-cost power electronics.

Nanostructure of Al-ZnO Thin Films on ITO/Glass Substrate Prepared via Sol-Gel Spin Coating Process

Solar energy is probably the most important source of renewable energy available today. ZnO is a potential material for the fabrication solar cell. Zinc oxide (ZnO) nano-structure semiconductors have been recently gained much attention in the electronic and optical device applications. ZnO is a compound semiconductor, which has a high extention band gap (E= 3.37 eV) at room temperature (RT) with a Wurtzite crystal structure. In particular ZnO can be employed as the transparent conducting oxide (TCO) in solar cell applications due to its high productivity, non-toxic, low cost, and excellent electrical conductivity. In this study, aluminum doped ZnO (AZO) polycrystalline films have been fabricated on ITO/substrates via a sol-gel spin-coating method. The quantity of aluminum doping in the solution was 4.0 %. After synthesis, the films were pre-heated at 300°C for 25 min and after that the films were inserted in a Tub-furnace and post-annealing at 450°C to 750°C for 1 h. The microstructural and structural properties of AZO films were studied through X-ray diffraction (XRD), UV-Vis NIR and scanning electron microscope (SEM) analysis. The TCO applications of the transmittance of samples were also examined. The results showed that the annealing temperature does not seriously affect on the transmittance of AZO films over the visible range.

Biased Photoresponse Analysis of Al–ZnO Heterojunctions with n- and p-Type Silicon

Al–ZnO/(n)Si and Al–ZnO/(p)Si heterojunction structures were fabricated by RF-sputtering of Al–ZnO thin film on Si substrates and their electrical and photoresponse properties were comparatively analyzed. The Al–ZnO/(n)Si heterojunction exhibited excellent diode behavior with an equivalent barrier height of 0.72 eV and an rectification ratio of $6.7 \times 10^{3}$ at ±0.5 V, while no rectifying behavior was observed for Al–ZnO/(p)Si device. Illuminated I–V analysis performed with different light intensities revealed excellent photoresponse properties and the strong dependence of the photocurrent on external bias for both Al–ZnO/(n)Si and Al–ZnO/(p)Si structures. The Al–ZnO/(n)Si structure requires smaller reverse bias than Al–ZnO/(p)Si for similar photoresponse. Based on dark I–V, illuminated I–V, and the energy band diagrams, photoresponse mechanisms were explained. In order to further understand the photoresponse mechanisms, quantum efficiency measurements were carried out, with applied external voltage bias. A general descriptive model was presented for the first time for the photogenerated current density in both Al–ZnO/(n)Si and Al–ZnO/(p)Si heterojunctions at different voltage bias.

Thermal processing of aqueous AZO inks towards functional TCO thin films

Aluminium doped zinc oxide is considered an interesting, earth abundant alternative to the transparent conductor indium tin oxide. In this respect, we synthesized Al-ZnO (AZO) thin films by a chemical solution deposition approach. Using water-based inks, the AZO thin films were printed in one single step on glass substrates in non-vacuum conditions. The drying process and the humidity of the atmosphere proved to be crucial during the thermal processing of the wet deposited thin films. To improve the understanding of the phenomena involved, the influence of these processing parameters on the final properties of the AZO thin films are investigated by FTIR, XRD, SEM, 1H and 27Al NMR and resistivity measurements. Optimal conditions were obtained by drying the wet thin film at 120 °C, followed by heating in a tube furnace until 500 °C under a 200 ppm O2/N2 atmosphere with a humidity controlled by bubbling the gas flow through 2 glass bottles containing water at 20 °C. AZO thin films with an resistivity of 2.54 × 10−2 Ω cm were obtained.

Structural and optical characterization of ZnO and AZO thin films: the influence of post-annealing

In the present study, ZnO and Al:ZnO (AZO) thin films were prepared by reactive RF sputtering on quartz substrates at a constant oxygen partial pressure and a typical sputtering power. Films were annealed at different temperatures in argon ambient in the oven to study their various structural and optical properties. It was understood that introducing Al into ZnO structure would affect the ZnO crystalline structure noticeably. It was observed that annealing had great influence on various properties of thin films while ZnO film showed low crystallinity, Al doping into ZnO structure pronounced significant improvement in both crystallinity and particle sizes. It was found that crystal structures, average crystalline sizes, and topology of all thin films were modified enormously by post-annealing. It was shown that films transparency fluctuated by annealing, in which the transparency of AZO thin film annealed at 500 � C was much greater than others. Annealing led to decrease optical band gap of all annealed films from 3.31 to 3.26 eV for ZnO and 4 to 3.4 eV for AZO films. Photoluminescence manifested that blue emission in as-deposited film led to two different blue and violet emissions in all AZO and ZnO films. It was identified that the emission intensity of AZO film annealed at 500 � C was 12 times more than other ZnO and AZO films.

Simultaneous enhancement of carrier mobility and concentration via tailoring of Al-chemical states in Al-ZnO thin films

Simultaneously achieving higher carriers concentration and mobility is a technical challenge against up-scaling the transparent-conductive performances of transparent-conductive oxides. Utilizing one order higher dense (∼1 × 1011 cm−3) plasmas (in comparison to the conventional direct current plasmas), highly c-axis oriented Al-doped ZnO films have been prepared with precise control over relative composition and chemical states of constituting elements. Tailoring of intrinsic (O vacancies) and extrinsic (ionic Al and zero-valent Al) dopants provide simultaneous enhancement in mobility and concentration of charge carriers. Room-temperature resistivity as low as 4.89 × 10−4 Ω cm along the carrier concentration 5.6 × 1020 cm−3 is obtained in 200 nm thick transparent films. Here, the control of atomic Al reduces the charge trapping at grain boundaries and subdues the effects of grain boundary scattering. A mechanism based on the correlation between electron-hole interaction and carrier mobility is proposed for degenerately doped wide band-gap semiconductors.

Sol–gel derived AZO thin film with unusual narrow dual emission

AZO (Al:ZnO) nanostructured thin film was prepared by a dip coating technique. An improved sol–gel method was used for the preparation of stable AZO sol with 2at% Al dopant concentration. Optical properties of AZO thin film have been studied by UV–visible absorption and photoluminescence spectroscopy. Scanning electron microscopy and X-ray diffraction pattern were performed to study the grain size and morphology of AZO thin films. Experimental observations confirmed that the deposited AZO thin film has potential for dual narrow emission in the blue and green regions. Transmission spectrum shows that the prepared thin film is able to transmit above 95% of the light in the visible region. The prepared thin film resistivity is also very low (5.0Ωcm).

Sol–gel derived Al and Ga co-doped ZnO thin films: An optoelectronic study

Al and Ga co-doped ZnO (AGZO) thin films with different doping contents of 0.5–4at.% were synthesized via sol–gel route using dip coating method and the results were compared to the single doped specimens Al:ZnO (AZO) and Ga:ZnO (GZO). All samples were highly transparent in visible region (T>85%) with band gap values around 3.3eV. Introduction of Al and Ga to the ZnO crystal structure decreased the crystallinity and reduced the particle size of the films. Electrical resistivity was investigated and engineered in this study as the main parameter. Single doped samples showed reduction of resistivity compared to the un-doped ZnO. In this regard, Ga was more efficient than Al in decreasing the electrical resistivity. Furthermore, samples with 1at.% Al and 1at.% Ga showed the minimum amount of electrical resistivity. Co-doping was performed with two different approaches including variable doping content (Al+Ga≠cte) and constant doping content (Al+Ga=0.5, 1, and 2at.%) for the sake of the comparison with single doped samples. Samples with Al=1at.% and Ga=1at.% showed the lowest electrical resistivity in AGZO samples of former approach. However, in latter approach the lowest resistivity was obtained in Al+Ga=2at.% sample. The results proved the capability of co-doped samples in optoelectronic industry regarding partially substitution of expensive Ga with Al and obtaining co-doped AGZO transparent conductive thin films with lower resistivity compared to conventional AZO thin films and also achieving commercial advantages compared to costly GZO thin films.