ZAO Thin Films Research Articles

High quality a-InGaZnO and a-ZrAlO deposited at 375 °C by spray pyrolysis for low voltage operation TFTs

We report the high-performance, bottom-gate a-InGaZnO (IGZO) TFT with high-k ZrAlO (ZAO) gate insulator by spray pyrolysis (SP). The a-IGZO/ZAO TFT exhibits the average saturation mobility of 23.12 cm2 V−1 s−1, subthreshold swing of 121 mV dec-1, ION/OFFratio of ∼108 with no hysteresis and low off-state current of ∼10-19A µm−1. In addition, the TFT exhibits good interface quality with less trap density (∼9x1010 cm−2) and conduction band tail state (∼4.3x1018 cm−3) extracted from TCAD fitting. The high-performance is attributed to the formation of uniform and dense a-IGZO and ZAO thin films with low defect density. Therefore, the SP a-IGZO/ZAO TFTs have great potential to be employed in low-cost, low driving voltage TFTs for display application.

Thin films derived from Zn(Al)O mixed metal oxides nanoparticles dispersed in polyethylene glycol: Structural, morphological and optical properties

In this study, Zn(Al)O thin films were produced using colloidal solution of Zn(Al)O nanoparticles dispersed in polyethylene glycol (PEG). Zn(Al)O mixed metal oxides were obtained by a simple pyrolysis of Zn–Al containing layered double hydroxide materials with different Al content. Survey of textural analysis of Zn(Al)O mixed oxides displayed characteristic peaks of ZnO structure. The calculated ratios of lattice parameters c/a were found to be 1.61 and 1.60 for 3-ZAO and 5-ZAO, respectively. The optical transmittance of the prepared thin films was not significantly affected by the increase in Al content; however, this increase changed the optical band gap from 3.27 eV to 3.33 eV. ZAO thin films, which are both cost-effective with good optical properties, have the potential to be an alternative to those used in many optical devices lately.

Zinc oxide-based current spreading layer behavior on the performance of P-side-up thin-film red light emitting diodes

Transparent conductive layers deposited on a GaP window layer were used to fabricate high-brightness p-side-up thin-film AlGaInP light emitting diodes (LEDs). Zinc oxide (ZnO) and aluminum-doped zinc oxide (ZAO) with an Zn:Al cycle ratio of 20:1 were grown by atomic layer deposition for comparison. The ZAO thin films reduced the droop in the external quantum efficiencies of the LEDs as well as the junction temperature, which result in increases in the light output power and thermal stability of the LEDs. The efficiency droops of the LEDs with the ZnO and ZAO thin films were 41% and 15%, respectively. The junction temperature of the LED with the ZAO thin film can be reduced to 39.6°C at an injection current of 700mA, which is lower than that of the LED with the ZnO thin film (58.1°C). The above results are promising for the development of ZAO thin films for applications in AlGaInP LEDs.

Metamorphosis of strain/stress on optical band gap energy of ZAO thin films via manipulation of thermal annealing process

We report on the growth of Al-doped ZnO (ZAO) thin films prepared by the sol–gel technique associated with dip-coating onto Corning 7740 glass substrates. The influence of varying thermal annealing (Ta) temperature on crystallisation behaviour, optical and electrical properties of ZAO films has been systematically investigated. All films are polycrystalline with a hexagonal wurtzite structure with a preferential orientation according to the direction 〈002〉. The metamorphosis of strain/stress effects in ZAO thin films has been investigated using X-ray diffraction. The as growth films have a large compressive stress of 0.55GPa, which relaxed to 0.25GPa as the Ta was increased to 500°C. Optical parameters such as optical transmittance, absorption coefficient, refractive index and optical band gap energy have been studied and discussed with respect to Ta. All films exhibit a transmittance above 80–90% along the visible–NIR range up to 1500nm and a sharp absorption onset below 400nm corresponding to the fundamental absorption edge of ZnO. Experimental results show that the tensile stress in the films reveals an incline pattern with the optical band gap energy, while the compressive stress shows opposite relation.

Study on Preparation and Photoluminescence Performance of High-Directional ZAO Nanorod Arrays

Al-doped zinc oxide (ZAO);nanorod arrays;thin film;preparation; photoluminescence. Abstract: ZAO thin films were deposited on glass substrates by sol-gel method and then by controlling processing parameters such as the amount of doped Al and stability, etc.well-aligned Al-doped ZnO nanorod arrays with a narrow diameter distribution were successfully grown on substrates by hydrothermal method, where the substrates were spin-coated with seed layer.The experiments show the 2% Al-doped and diameter about 50nm of ZAO nanorod arrays has the best photoluminescence and surfactants can promote the growth of ZAO rod-like nano-structures and contribute to the formation of ZAO nanorod arrays with highly oriented nanorod arrays.

Preparation and Properties of ZnO/ZAO Double-Layers Thin Films on the Substrate of Glass

Aluminium zinc oxide(ZAO) thin films were deposited on soda-Lime-Silica glass substrate by middle frequency power magnetron sputtering. Then zinc oxide(ZnO) thin films were deposited above ZAO thin films by electrochemical deposition method at different time. ZAO thin films and ZnO/ZAO double-Layers thin films were characterized by X-Ray diffraction(XRD) and scanning electron microscope(SEM). A four-Point probe was used to determine the resistivity of the films. The optical transmittance of ZAO films and ZnO/ZAO films was measured by UV-Visible spectrum. The results represent that the transmittance of ZAO/ZnO thin films decreases gradually with deposition time increasing. When the deposition time is 5 minutes, the maximum transmittance of ZnO/ZAO films reaches to 85% at wave length from 400nm to 600nm, and the thickness and resistivity of thin film are 610nm and 2.04×10-3Ω•cm, respectively. However, the thickness and resistivity are highest when the deposition time is 20 minutes, which reaches to 808nm and 1.2×10-2Ω•cm. Meanwhile, the lattice constants a and c of ZAO/ZnO thin films demonstrate an expansion with deposition time increasing. In essence, good-Quality double-Layers thin films of ZnO/ZAO play an important role in CIGS solar cells.

Preparation and Photoelectric Properties of High-Directional Al-Doped Zinc Oxide Nanorod Arrays

ZAO nanorod arrays with high preferential c-axis orientation and excellent photovoltaic performance were prepared in order to apply it extensively. Aluminum- doped zinc oxide thin films were deposited on glass substrates by sol-gel method.And then by controlling processing parameters such as the amount of doped aluminum and stability, etc.well-aligned Al-doped ZnO nanorod arrays with a narrow diameter distribution were successfully grown on substrates by hydrothermal method, where the substrates were spin-coated with seed layer.The experiments show that the 2% aluminum-doped and diameter of about 50nm of ZAO thin film nanorod arrays has the best performance photoluminescence and surfactants can promote the growth of ZAO rod-like nano-structures and contribute to the formation of ZAO nanorod arrays with highly oriented nanorod arrays.

Effects of Substrate Temperature on ZAO Thin Film Prepared by DC Magnetron Reactive Sputtering

Abstract The effects of substrate temperature on the resistivity and transmittance of ZAO thin films prepared by DC magnetron reactive sputtering have been investigated. The properties of the samples have been analyzed through Hall effect, X-ray diffraction and SEM. The results show that carrier concentration, Hall mobility and crystallinity of the films depend obviously on the deposition temperature. The film deposited at the range 200-250°C has lower resistivity and higher transmittance.

Properties of Al Doped ZnO Thin films by DC Reaction Magnetron Sputtering

The high quality ZAO thin films were successfully produced by DC reaction magnetron sputtering technology. The XRD，electrical and optical properties of films are particular investigated. The results show that ZAO films are polycrystalline hexagonal wurtzite structure，and Al2O3 crystal phase are not found. At the same time，the high quality ZAO films with the minimum resistivity of 4.5x10-4Ω•㎝, the transmittance in visible region above 80% and the reflectivity in IR region above 70% are gained.

Thickness effect on structure and properties of ZAO thin films by RF magnetron sputtering at different substrate temperatures

Al-doped ZnO (ZAO) films, having film thickness of about 50–1200 nm, were deposited at substrate temperature of 100–300 °C by radio-frequency magnetron sputtering. Structural, electrical, and optical properties of as-deposited ZAO films have been studied as a function of film thickness and substrate temperature. The investigation of X-ray diffraction indicates that the crystalline quality of the film improves and its stress relaxes with increasing film thickness or substrate temperature, and preferred (0 0 2) orientation is found at substrate temperature above 100 °C. By the observation under scanning electron microscope, columnar structure can be obviously observed from cross-section of the films with increasing film thickness at substrate temperature above 100 °C; the surface morphology can exhibit nanocrystalline, honeycomb, or hillock structure, depending on film thickness and substrate temperature. Hall effect measurements reveal that the decrease of resistivity of the film is generally accompanied by the increase of carrier concentration and mobility with increasing film thickness or substrate temperature. It is speculated that the main scattering mechanism in as-deposited ZAO films is intercrystallite boundary scattering. The transmission spectra measurements of ZAO films indicate that average transmittance between 400 and 800 nm decreases from about 86% to 70% with increase in film thickness. The obtained energy gap ( E g ) of the films at different substrate temperatures is found in order of 200 °C>300 °C>100 °C, which can be attributed to high carrier concentration and compressive stress at 200 °C, but markedly low carrier concentration at 100 °C. With increase in film thickness, the decrease in compressive stress and/or increase in crystallite size result in the decreased or unchanged tendency of E g of the films although the carrier concentration increases.

Analysis of ZAO Thin Films by DC Reaction Magnetron Sputtereing

The high quality ZAO thin films were produced by DC reaction magnetron sputtering technology. The XRD, electrical and optical properties of ZAO thin films were particularly investigated. The results show that ZAO films are polycrystalline hexagonal wurtzite structure，and Al2O3 crystal phase are not found. At the same time，the high quality ZAO films with the minimum resistivity of 4.5x×10-4Ω·㎝, the transmittance in visible region above 80% and the reflectivity in IR region above 70% are gained.

Effects of Substrate Temperature on ZAO Thin Film Prepared by DC Reactive Magnetron Sputtering

The effects of substrate temperature on the resistivity and transmittance of ZAO thin films prepared by DC magnetron reactive sputtering have been investigated. The properties of the samples have been analyzed through Hall effect, X-ray diffraction and SEM. The results show that carrier concentration, Hall mobility and crystallinity of the films depend obviously on the deposition temperature. The film deposited at the range 200-250°C has lower resistivity and higher transmittance.

Influence of Vacuum-Annealing Temperature on the Properties of Direct Current (DC) Magnetron Sputtered ZAO Thin Films

This study focused on the properties of optics and electrics as well as microstructure and morphology of the ZAO thin films which were annealed at different temperature. After vacuum-annealed at 160° or above, the films' quality can be significantly improved. The growth along (002) direction of ZAO thin films were found to be faster than the ZAO films which were not treated and reached a maximum at 330°. FWHM decreased to 0.74°at 330° and grain size grew to 12.02039nm at 400°. The shape of crystal grain changed from anomalous formation to roundness. At the same time, the resistivity of ZAO thin films decreased and reached a minimum of 9.36×10-4Ω•cm while the average transmittance increased to 82% in visible region.

Effects of Argon-Oxygen Ratio and Sputtering Power on Optical Properties of ZnO:Al Thin Films Fabricated by RF Magnetron Sputtering

Al-doped ZnO (ZAO) thin film with good performance was prepared by radio frequency (RF) magnetron sputtering technology under optimized process conditions. The crystallized characteristic and microstructure of the prepared samples were investigated by X-ray diffraction (XRD) pattern and atomic force microscopy (AFM). The optical transmittance spectra was employed to investigate the dependence of the optical performance of the ZAO film on the process conditions, such as argon-oxygen pressure ratios and sputtering powers, which revealed that the transmittance in the visible spectrum is first increased and then decreased as the argon/oxygen pressure ratios increased from 7/1 to 10/1. When the argon/oxygen pressure ratio is 9/1, the transmittance adds up to the maximum. In addition, as the RF sputtering power increases from 80W to 120W, the transmittance of the films is slightly declined with an average transmittance of above 80%; and with the increase of the sputtering power to 140W and 160W, the maximum transmittance of the film obviously decreases below 75%. Moreover, the electrical properties of ZAO thin films were measured by the four-probe tester. The resistivity of the film is less than 10-3 Ω • cm, demonstrating that it have a good electrical performance.

Study on XRDK Optical and Electrical performance of Transparent Conducting ZnO:Al(ZAO) Thin Films

The ZAO (ZnO: Al) thin films were prepared by DC reactive magnetron sputtering technique. The XRD electrical and optical properties of films are particular investigated. The results show that ZAO films are polycrystalline hexagonal wurtzite structure, and we are not find Al2O3 crystal phase. At the same time, we gained the high quality ZAO films with the minimum resistivuty of 4.5×10-4 Ω · cm, the transmittance in visible region above 80% and the reflectivity in IR region above 70%.

Analysis on the process of ZAO films by DC magnetron reactive sputtering

The ZAO (ZnO:Al) thin films were prepared by DC reactive magnetron sputtering technique. The relationship between the process parameters and the organizational structure, optical and electrical properties was studied. Through optimizing the process parameters, an optimal preparation parameter can be obtained. Using the optimal parameters to prepare the ZAO thin films, the resistivity of the ZAO film is as low as 4.5×10−4 Ω·cm and the average transmissivity in the visible region is around 80%, the optical and electrical properties meet the application requirements.

Influence of the gas flow of Argon and the distance between substrate and plasma on properties of Al-doped zinc oxide films

Al-doped ZnO(ZAO) films were deposited by DC magnetron sputtering using facing zinc oxide targets at room temperature and in argon atmosphere. The effects of the gas flow of Argon and the distance between substrate and plasma on the properties of the ZAO thin films were characterized by several techniques. By optimizing the craft of preparation, the electrical resistivity as low as 3.3×10-4 Ω·cm and the optical transmittance over 80% in the visible range were obtained for these thin ZAO films. Therefore, the ZAO thin films were suitable for the window layers of n-i-p thin film solar cells or transparent conductive films.

Preparation of Mg and Al co-doped ZnO thin films with tunable band gap

Al （Al2O3，2wt%） doped ZnO thin films （ZAO） with tunable band gap，alloyed with different Mg contents （1wt%，3wt% and 5wt%），were prepared by radio frequency magnetron sputtering on glass substrates and annealed at 500℃ in air. The optical and electrical properties of the films were measured by X-ray diffractometer，four-point probe method，Hall-effect configuration，and UV-VIS spectrophotometer. The results show that the Mg co-doped ZAO thin films have a wurtzite structure with （002） preferred orientation. Compared with ZAO film，the optical transmission of Mg co-doped ZAO thin films in the ultraviolet region increases and the average optical transmissions in the visible region is greater than 85%，except the 5wt% Mg doped films. The band gaps of ZAO and Mg co-doped ZAO thin films can be modulated from 344 eV to 351 eV by increasing the Mg content from 1wt% to 5wt%. For 1wt%，3wt% and 5wt% Mg doping，the Mg co-doped ZAO thin films have the resistivity of 12×10-3，37×10-3 and 85×10-3 Ω·cm，respectively. Stokes shifts of 20，14 and 50 meV were observed for doping of 1wt%，3wt%，and 5wt% Mg contents. We find that a large Mg doping content will degrade the crystal quality of Mg co-doped ZAO thin films，decrease the optical transmissions in the visible region and decrease the carrier mobility in the films. Therefore，the resistivity of Mg co-doped ZAO thin films increases with the Mg doping content.

Effects of Atomic Oxygen Irradiation on Transparent Conductive Oxide Thin Films

Transparent conductive oxide (TCO) thin film is a kind of functional material which has potential applications in solar cells and atomic oxygen (AO) resisting systems in spacecrafts. Of TCO, ZnO:Al (ZAO) and In2O3:Sn (ITO) thin films have been widely used and investigated. In this study, ZAO and ITO thin films were irradiated by AO with different amounts of fluence. The as-deposited samples and irradiated ones were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Hall-effect measurement to investigate the dependence of the structure, morphology and electrical properties of ZAO or ITO on the amount of fluence of AO irradiation. It is noticed that AO has erosion effects on the surface of ZAO without evident influences upon its structure and conductive properties. Moreover, as the amount of AO fluence rises, the carrier concentration of ITO decreases causing the resistivity to increase by at most 21.7%.

Effects of γ-Ray Irradiation on Structure and Properties of ZnO:Al Thin Film

ZnO:Al(ZAO) thin film is a kind of transparent conductive functional material which has a potential application in the solar cell and Atom Oxygen resisting systems of spacecrafts. High performance ZAO thin films were prepared by reactive magnetron sputtering and then irradiated by γ-ray with different dose or rate of irradiation. The as-deposited sample and irradiated ones were characterized by X-ray Diffraction, Scanning Electron Microscopy and Hall-effect measurement to investigate the dependences of the structure, morphology and electrical properties of ZAO on the dose and rate of γ-ray irradiation. Measurement of Positron Annihilation Doppler-Broadening Spectroscopy was carried out to study the variation of the defects in ZAO thin films before and after irradiation. It is indicated that γ-ray will excite the carriers, which are electrons in ZAO. A high rate of γ-ray irradiation could slightly destroy the bonds of Zn-O and decrease the crystallinity, while the effect of low rate irradiation is similar to heat annealing and increase the crystallinity of ZAO thin films. γ-ray has no apparent influences on the negative vacancy defects in ZAO thin film.