Abstract Al-doped ZnO Films Research Articles

Effect of oxygen flowrate on optical and electrical properties in Al doped ZnO thin films

Al doped ZnO (AZO) thin films were synthesised on quartz glass substrates by pulsed laser deposition (PLD) method at different oxygen flowrates. The structure, composition, optical and electrical properties in the films were investigated. The result of surface profiler shows that with the increase in oxygen flowrate from 10 to 70 sccm, the films’ thickness increases from 526 to 706 nm. X-ray diffraction results show that the crystalline quality of the films is improved with the increase in oxygen flowrate; energy dispersive spectroscopy results exhibit that the Al content in the films increases from 4·32 to 6·45% with the increase in oxygen flowrate. The former leads to the weakening of grain boundary scattering; consequently, Hall mobility will increase, and the latter results in the increase in carrier concentration. As a result, the electrical resistivity in AZO films decreases from 10·92×10−3 to 2·34×10−3 Ω cm with increasing the oxygen flowrate. Moreover, the increase in carrier concentration induces the slight widening of optical band gap due to the Burstein–Moss effect with the increase in oxygen flowrate. For AZO thin films grown by the PLD method, the control of oxygen flowrate is a simple method to obtain adjustable electrical resistivity, optical band gap and ultraviolet emission.

Effect of Si substrate orientation on morphology and electrical properties of ZnO∶Al films

Al doped ZnO films (AZO) have been deposited on (100), (110) and (111) Si substrates by RF magnetron sputtering to investigate the influence of Si substrate orientation on the morphology and electrical properties. It has been found that all these films have columnar structures. The grain size of the AZO films deposited on (100), (110) and (111) Si substrates increases monotonically, thereby resulting in a decrease in the resistivity. The interfacial-geometry analysis shows a decrease in the degree of interface misfit on (100), (110), and (111) Si substrates. Therefore, there is an obvious correspondence between the grain size of the films and the interfacial-misfit degree, which indicates that the interface misfit is a key factor dominating the grain size, and, hence, the film resistivity.

Infrared reflective property of AZO films prepared by RF magnetron sputtering

Al doped ZnO (AZO) films were prepared on glass substrates by radio frequency (RF) magnetron sputtering technology. Surface morphology, crystal structure, chemical composition, UV-visible transmittance, electrical and infrared properties of the AZO films were investigated by atomic force microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Spectrophotometer, Hall measurement system and Fourier Transform infrared spectroscopy, respectively. The results indicate that AZO films with strong c-axis preferred wurtzite structure were successfully prepared by RF magnetron sputtering at room temperature. The average visible transmittance and infrared reflection rate (from 1·5 to 25 μm) of the deposited films was 84·8 and 30%, respectively. The study creates a sound basis for investigating the infrared properties of AZO films for future heat shielding films.

Influence of external magnetic field on properties of aluminum-doped zinc oxide films prepared by RF magnetron sputtering

Al-doped ZnO (AZO) transparent conductive oxide films were prepared by RF magnetic sputtering. An external magnetic field was applied to the traditional magnetron sputtering system. The influence of the external magnetic field on the crystalline structure, surface topography and photoelectric properties of the AZO transparent conductive film have been studied. XRD diffraction patterns show that under the same processing condition, the intensity of (002) diffraction peak is significantly increased with the external magnetic field, suggesting a higher degree of c-axis preferred orientation. Scanning electron microscope shows that the external magnetic field can enlarge the grain size and density of films; the surface topography of the AZO films deposited without an external magnetic field is wormlike. Deposition rate and square resistance test results show that in an external magnetic field, the deposition rate will increase from 13.04 nm/min to 19.93 nm/min, and the sheet resistance reduce to 12.88 Ω /□ from 30.74 Ω /□ at a sputtering time of 90 min. Optical transmittance spectra shows that the average transmittance of all the films in visible light spectrum is over 85% when the sputtering time is not more than 60 min, while the external magnetic field has little effect on the transmittance of the films, but making a larger blue shift of the absorption edge. Ansys software is used to simulate the two-dimensional magnetic field distribution above the target. Results show that the intensity of the horizontal magnetic field and the uniformity of it are improved by the external magnetic field, the secondary electrons near the target are tightly bound, leading to a much larger target current intensity. So the deposition rate, surface topography and photoelectric properties of the AZO films are improved.

Influence of hydrogen annealing on structure and optoelectronic properties in Al doped ZnO thin films

Al doped ZnO (AZO) thin films are of significant interest for flat panel displays, solar cells, etc. In this regard, AZO films were prepared in Ar atmosphere by radio frequency magnetron sputtering with an AZO (2 wt-%Al2O3) ceramic target at room temperature. To investigate the influence of hydrogen related defects on the structure and optoelectronic properties in AZO films, the prepared films were annealed in Ar+H2 ambient at different temperatures (100–500°C). The results show that the films’ crystallinity becomes better and the resistivity decreases with the increase in annealing temperature. The lowest resistivity of 2·79×10−3 Ω cm is obtained after 500°C hydrogen annealing, which decreases by about four orders of magnitude compared to the resistivity of as deposited film. The improvement of electrical properties is attributed to the formation of H related defects and desorption of weakly bonded oxygen species near grain boundaries in AZO films after H2 annealing treatment, and the corresponding physical mechanism was discussed. It is proved that hydrogen annealing is an effective method for the improvement of electrical properties in AZO thin films. The optical bandgap energy of the films obviously increases with the increase in annealing temperature due to Burstein–Moss effect.

Processing and characterisation of nanostructured Al doped ZnO antireflection films

Al doped ZnO films (3 at-%) were developed on soda lime glass substrate by electroless deposition. The films were characterised by X-ray diffraction (XRD), field scanning electron microscope (FESEM/EDS), atomic force microscope (AFM) and UV visible spectrophotometer. X-ray diffraction analysis indicates that preferential growth of the films are (101) reflection peak in the 400, 500 and 600°C annealed films. FESEM surface and cross-section analysis exhibit that Al doped ZnO film has dense and compact grains as compared to undoped ZnO film. Film is composed of Zn, Al and O is confirmed by EDS analysis. Surface roughness of the film is determined by AFM. The Al doped ZnO films exhibit excellent optical transmittance (more than 80%) and minimum absorbance spectra in visible range 400–800 nm wavelength. Al doped ZnO film annealed at 500°C is suitable for antireflection coating in silicon solar cell.

Performances of GaN-based LEDs with AZO Films as Transparent Electrodes

Al-doped ZnO(AZO) thin films were prepared by pulsed laser deposition under different oxygen pressures.AZO films with highly transparent conductive properties were obtained at 0.1 Pa.AZO films were used on GaN-based light-emitting diodes(LEDs) as transparent contact layers.At a forward current of 20 mA,the 520 nm electroluminescence peak was evidently observed,with a high working voltage of 10 V.The brightness of the chip was enhanced as the forward current increased.Secondary ion mass spectra revealed that the high working voltage of the LED might be triggered by the change of material conductivity and the passivation layer formed at the AZO/GaN interface.

Effect of Sputtering Pressure on Al-doped ZnO Films by DC Magnetron Sputtering

Al-doped ZnO (AZO) films were deposited on the glass substrates by direct current magnetron sputtering using different sputtering pressures ranging from 0.2 Pa to 2.2 Pa. Microstructure, phase, electrical and optical proper- ties of AZO films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), four-point probe and UV-Vis spectrophotometer, respectively. The results revealed that the deposition rate decreased with the in- creasing sputtering pressure according to Keller-Simmons model; the crystalline phase of all films was hexagonal wurtzite and the preferred orientation changed with the sputtering pressure; the surface morphology greatly depended on the sputtering pressure and the film deposited at 1.4 Pa showed low resistivity (8.4×10 −4 Ω·cm), high average

Effect of Al concentration on the structural, electrical, and optical properties of transparent Al-doped ZnO

Al-doped ZnO (AZO) films have been deposited on sapphire substrates at 400 °C for various Al doping concentrations (nAl) from 0 to 5 wt.% by RF magnetron sputtering and were subsequently annealed at 600 ∼ 800 °C for 3 min. The AZO films show the best structural, electrical, and optical properties at nAl = ∼2 wt.%, as demonstrated by Hall-effect, photoluminescence, X-ray diffraction, and optical transparency measurements. The nAl-dependent experimental results are discussed based on possible physical mechanisms. These studies provide a simple method of controlling nAl for optimizing the properties of AZO films for use as transparent conductive oxides.

The Electrical and Optical Properties of Al-Doped ZnO Thin Films Prepared by Atomic Layer Deposition

Al-doped ZnO (AZO) thin films (~100nm) with low electrical resistivity and high transparency have been prepared by atomic layer deposition on glass and Si(111) substrates at 200 °C with different doping sequence. The films were systematically analyzed using X-ray diffraction, scanning electron microscope (SEM), UV-vis spectroscopy and Hall measurement. XRD patterns showed that all the films were well crystallized with hexagonal wurtzite structure with preferred orientation along (100) plane. The resisitivity of films deposited with doping sequence of DEZ/TMA/H2O was lower than that with other doping sequences. Results from SEM showed a worm-like shape and similar grain sizes of AZO films. Optical transparency of AZO films was measured to be >90% for wavelengths of 400-1000 nm.

Annealing Effects on Structural and Magnetic Properties of Al doped ZnO Thin Films

Al doped ZnO films have been prepared by dc magnetron sputtering. These films were annealed in different atmosphere and temperature. The crystal structures were analyzed by x-ray diffraction (XRD), and the magnetic properties were measured by a Physical Properties Measurement System (PPMS) with the magnetic field paralleled to the films plane. The results show the microstructure and magnetic properties were influenced by annealing atmosphere. Compared to the films annealed in vacuum, the films annealed in air shows obvious room temperature ferromagnetism, the magnetic moment increases about an order of magnitude. The room temperature ferromagnetism may be associated with a charge transfer between Al and Zn and the variational position of Al in ZnO films in different annealing ambience.

Effects of thickness for Al doped ZnO thin films on their microstructure and magnetic properties

Al doped ZnO films of different thickness have been prepared on glass substrates by dc magnetron sputtering, these films were annealed in different atmosphere . The crystal structures were analyzed by x-ray diffraction (XRD), and the magnetic properties were measured by a Physical Properties Measurement System (PPMS) with the magnetic field paralleled to the films plane. The results indicate that with increase of the thickness, the crystallinity of the thin films gets better and the crystallites of the Al doped ZnO thin films increase gradually, whereas the internal stresses decreased. The results show the films annealed in air shows obvious room temperature ferromagnetism. With the increase of the film thickness the saturation magnetization is enhanced, and the coercivity is weakened.

Structure and Photoluminescence Properties of ZnO:Al/Porous Silicon Thin Films

Al doped ZnO (AZO) films were deposited on porous silicon (PS) substrates by a reactive rf-cosputtering process from two targets of ZnO and Al. The effect of ZnO target rf-sputtering power on the structural and photoluminescence (PL) properties of AZO/PS heterojunctions were studied. Strong monochromatic blue emission located at 2.78 eV was observed for the AZO films deposited at 150 W. Freshly prepared PS showed an emission band in the green spectral region. We show that deposition of AZO on PS does not degrade the skeleton of the PS and enhance the PL intensity. The PL band shifted to the high energy for AZO films deposited on PS and the intensity became stable.